bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of a co‐occurring aphid on the susceptibility of the Russian wheat aphid to lacewing predators
Authors: Bergeson Erin , Messina Frank J.
Published: October 2003

Previous field experiments indicated that the presence of the bird cherry‐oat aphid, Rhopalosiphum padi (L.), on perennial grasses can decrease the effectiveness of predatory lacewings, Chrysoperla plorabunda (Fitch), in reducing populations of the Russian wheat aphid, Diuraphis noxia (Mordvilko). We tested the hypothesis that R. padi deflects predation away from D. noxia because it feeds in sites that are more accessible to predators. We quantified the behavior of lacewing larvae on crested wheatgrass plants bearing either D. noxia alone or an equal mixture of D. noxia and R. padi. On non‐flowering plants, R. padi typically occurred on leaf sheaths or open blades, and was encountered and captured more often than D. noxia, which usually fed within immature, rolled leaves. Overall time‐budgets of lacewings did not differ between the pure‐D. noxia and mixed‐species treatments, but >75% of the time spent consuming aphids in the mixed‐species treatment was devoted to R. padi. On flowering plants, D. noxia usually aggregated on the flag leaf below the inflorescence, whereas R. padi occurred mostly on leaf sheaths. Predators again captured R. padi more often than D. noxia, and spent more time consuming aphids in the mixed‐species treatment than in the pure‐D. noxia treatment. These behavioral observations support the hypothesis that non‐target prey can hamper the short‐term effectiveness of biological‐control agents against D. noxia.
Expression of early and late‐emerging phenotypes in both diapausing and non‐diapausing Delia radicum L. pupae
Authors: Biron D. , Langlet X. , Boivin G. , Brunel E.
Published: October 2003

The presence of early and late phenotypes of Delia radicum L. (Diptera: Anthomyiidae) has been attributed to the existence of differences in development after diapause. The criteria for the early phenotype is emergence in less than 20 days at 20 °C (320 DD above 4 °C) and more than 30 days at 20 °C (280 DD above 7 °C + 320 DD above 4 °C) for the late phenotype. The emergence pattern of 10008 non‐diapausing D. radicum pupae reared at 20 °C, L16:D8 and 60% r.h. showed an asymmetrical bimodal distribution similar to the emergence pattern of 477 (1994) and 326 (1995) diapausing pupae from the field. When reared individuals were segregated based on their emergence pattern and reared separately, the proportion of early phenotype increased from 61 to 96% in three generations, while the proportion of late phenotype stayed at 78 to 80% during three generations. These results indicate clearly that diapause is not necessary for the expression of the early and late phenotypes. The presence of these two phenotypes probably enables D. radicum to optimize the use of the available resources, to ensure that a sizeable proportion of the larval population enters diapause and to maintain its distribution throughout the holarctic region (35 to 68 °N).
Survival, fecundity and fertility of Bactrocera oleae, as affected by amino acid analogues
Authors: Zografou E. N. , Tsiropoulos G. J. , Margaritis L. H.
Published: October 2003

The effect of twenty five amino acid analogues at various concentrations upon the adult olive fruit fly Bactrocera oleae Gmelin (Diptera: Tephritidae), was tested. Insect survival was significantly shortened by the following amino acid analogues: (in parentheses are indicated the antagonized amino acids) D‐cycloserine (alanine), L‐glutamic acid‐γ‐hydrazide (glutamine), DL‐allyl‐glycine (cysteine), L‐canavanine (arginine), L‐methionine‐DL‐sulfoximine (methionine) and 3,4‐dehydro‐DL‐proline (proline). Fecundity was significantly reduced by the same analogues plus aminoethanesulfonic acid (glycine), taurine (alanine), L‐norvaline (leucine), a‐methyl‐DL‐serine (serine), DL‐hydroxyglutamic acid (glutamic acid), (S)‐2‐(aminoethyl)‐L‐cysteine (lysine), a‐methyl‐DL‐methionine (methionine) and a‐methyl‐DL‐histidine (histidine). All the above amino acid analogues also depressed egg‐hatching with the exception of taurine, DL‐hydroxyglutamic acid, DL‐allyl glycine, a‐methyl‐DL‐methionine and a‐methyl‐DL‐histidine. Finally, y‐glutamyl‐p‐nitroanilide (glutamic acid), crotyl‐glycine (methionine), DL‐7‐azatryptophan and 5‐methyl‐DL‐tryptophan (tryptophan), DL‐1,2,4 triazole‐3‐alanine (histidine) and DL‐pipecolic acid (proline) did not affect any of the parameters tested.
Chemoreception of oviposition inhibiting terpenoids in the diamondback moth Plutella xylostella
Authors: Qiu Yu‐Tong , van Loon Joop J.A. , Roessingh Peter
Published: October 2003

The effects of six terpenoids and two terpenoid containing extracts of the neem tree (Azadirachta indica A. Juss.) on oviposition by the diamondback moth (Plutella xylostella L., Yponomeutidae: Lepidoptera) were tested. Two drimane terpenoids, the sesquiterpenoid polygodial and the neem extract Margosan‐O exerted significant inhibitory effects at the dosages tested. Ablation experiments showed that both antennae and fore‐tarsi contributed to mediation of the inhibition by a drimane. Location of chemosensilla on prothoracic tarsi and ovipositor was examined by scanning electronmicroscopy. Electrophysiological recordings from ovipositor and tarsal taste sensilla showed that distilled water produced distinct responses from one neuron. In tarsal sensilla, ethanol and drimane solutions produced responses from two neurons, one of which might be the water cell that fired at a reduced rate. A drimane significantly decreased the responses of tarsal chemoreceptors to a cabbage leaf extract, which is a possible sensory mechanism leading to behavioural avoidance of this compound.
Habitat diversification tactic for improving biological control: parasitism of the western grape leafhopper
Authors: Murphy Brook C. , Rosenheim Jay A. , Dowell Robert V. , Granett Jeffrey
Published: October 2003

In a previous study we demonstrated greater abundance of the parasitoid Anagrus epos (Girault) in grape vineyards located downwind of prune trees that function as overwintering habitats. This study examines whether these higher A. epos numbers translated into higher egg parasitism rates of the grape leafhopper, Erythroneura elegantula (Osborn). Paired commercial wine‐grape vineyard plots, one with and one without adjacent prune trees, were studied within a complete block design in northern and central California. A. epos was the key mortality factor affecting E. elegantula eggs. Point estimates of A. epos parasitism rates were significantly greater in vineyards associated with prune trees during the first E. elegantula generation in both 1991 and 1992. No consistent differences in parasitism rates were observed during the second or third generations. The results indicated that prune trees enhance early season parasitism rates. Cumulative estimates of egg parasitism across E. elegantula generations demonstrated that enhanced early‐season parasitism resulted in a net season‐long increase in the degree of mortality imposed by A. epos on E. elegantula eggs. Two factors were found to influence parasitism rates: the abundance of early‐season A. epos adults moving into vineyards and the density of E. elegantula eggs in vineyards. Our results indicate that diversification of vineyards using prune trees supports overwintering populations of a specialist parasitoid and thereby alters host‐parasitoid interactions to favor enhanced parasitism in vineyards.
Are differences in life history parameters of the pine beauty moth Panolis flammea modified by host plant quality or gender?
Authors: Leather S. R. , Beare J. A. , Cooke R. C. A. , Fellowes M. D. E.
Published: October 2003

Pine beauty moth (Panolis flammea D&S, Lepidoptera: Noctuidae) were reared individually from egg hatch to pupation on one of three host plants, Pinus sylvestris (native host plant), Pinus contorta (Central Interior seed origin – good quality introduced host) and P. contorta (Alaskan seed origin – poor quality introduced host). After emerging from the pupae the adult moths were confined to a Skeena River seed origin of P. contorta. Female pupal weight and adult life span were significantly higher on P. sylvestris than on the two lodgepole pine seed origins. Development time was, however, not significantly different between treatments, but larval mean relative growth rate was found to be negatively correlated with birth weight and positively correlated with pupal weight. The time to emerge from the pupa was also not significantly different between treatments. However, there were marked differences between the genders. Male moths lost a significantly greater proportion of their weight over the pupal stage but lived significantly longer as adults than the females. Female moths emerged from the pupal stage significantly sooner than male moths. There was no apparent advantage of large birth size when looked at in terms of subsequent performance. These results are discussed in light of current life history theory.
Endocrine background of how 20‐hydroxyecdysone agonist, RH 5849, influences diurnal pattern of pupation in Spodoptera littoralis
Authors: Pszczolkowski Maciej A. , Kuszczak Barbara , Smagghe Guy
Published: October 2003

Under laboratory conditions (L16:D8, 24°C, r.h. 80%), applying of an ecdysone agonist, RH 5849, (1,2‐dibenzoyl‐1‐tert‐butylhydrazine) onto final instar larvae of Spodoptera littoralis (Boisd.), Noctuidae, Lepidoptera, delayed or advanced the time of pupation depending on the time of treatment. This response was dose‐dependent. In addition, non‐lethal doses of RH 5849, ranging from 0.05 to 10 μg/larva were used. Following treatment of S. littoralis larvae with 5 μg RH 5849 the endogenous ecdysteroid level was increased or decreased depending on the time of application. Based on the results presented, we suggest that potential users of non‐steroidal ecdysone agonists should consider the proper circadian timing of application in the field.
High temperature induced diapause in the cotton bollworm Helicoverpa armigera
Authors: Nibouche Samuel
Published: October 2003

In laboratory studies, Helicoverpa armigera (Hübner) (Lep. Noctuidae) from Burkina Faso exhibited pupal dormancy induced by high temperatures. Exposure to 37 °C from the 3rd larval stage caused 94.7% of males to diapause but only 60.9% of females. No influence of daylength (12 and 16 h) was observed. Induction by high temperatures must begin during the larval stage to be effective. The pupal stage is not sensitive to induction. After storage at 37 °C for 60 days, 64.3% of dormant pupae survived and most of them resulted in adult emergence. After storage at 37 °C for 85 days, no dormant pupae survived. The development of dormant pupae is resumed after about 20 days at 21 °C whatever the duration of prior exposure to 37 °C (7, 14 or 30 days). There is no delay in non‐dormant pupae kept at 21 °C. The possible role of this ‘hot thermal diapause’ in the life history of H. armigera in Burkina Faso is discussed.
Trees or stores? The origin of migrating Prostephanus truncatus collected in different ecological habitats in southern Benin
Authors: Borgemeister C. , Tchabi A. , Scholz D.
Published: October 2003

Migrating Prostephanus truncatus (Horn) (Col.: Bostrichidae) were collected weekly with pheromone‐baited funnel traps at three different sites in southern Benin for 12 months. One site was located in a primary forest, one in a peri‐urban area, and one in a region with intensive agriculture. The sex of the trapped beetles was determined. The gut‐content of the specimens was analyzed for remains of lignin and starch, the former indicating recent feeding on woody, the latter on a starchy substrate, such as stored maize or dried cassava. At all locations, the sex ratio of migrating P. truncatus was significantly female‐biased, with the greatest proportion of females trapped at the peri‐urban site. At the forest site, most beetles had lignin in their guts, while the proportion of beetles containing starch was highest in the peri‐urban site. Approximately equal proportions of beetles with either starch and lignin were trapped in the region with intensive agriculture. The results are discussed with regard to the population dynamics of P. truncatus in different habitats and the flight activity of the beetles.
Selection of biting sites on a human host by Anopheles gambiae s.s., An. arabiensis and An. quadriannulatus
Authors: Dekker Teun , Takken Willem , Knols Bart G. J. , Bouman Edwin , van de Laak Stephan , de Bever Arjan , Huisman Piet W. T.
Published: October 2003

The selection of biting sites on a human host of three closely related mosquito species belonging to the African Anopheles gambiae complex (Diptera: Culicidae), Anopheles gambiae Giles s.s., An. arabiensis Patton and An. quadriannulatus Theobald, was investigated under controlled laboratory conditions. Although these species differ in host preference, they all showed a significant preference to bite the legs and feet, suggesting that a mutual not specifically human factor was involved in the selection of biting sites. In subsequent experiments with An. gambiae s.s. this factor was revealed by altering the position of the test person. In experiments with the test person sitting on a stool, the legs and feet were significantly preferred as biting sites, whereas lying on the ground, with the legs and feet sticking up, the latter body parts were bitten significantly less than the body parts closest to the ground (head, trunk and arms). The results indicate that mainly convection currents along the host are used by members of the An. gambiae complex in selecting a biting site. In contrast to An. gambiae s.s. and An. arabiensis, large numbers of bites by An. quadriannulatus also occurred on the head, possibly in response to exhaled breath. It is concluded that the selection of biting sites of members of the Anopheles gambiae complex is guided by convection currents and partially mediated by host odours.
Geographical variation in insect developmental period: effect of host plant phenology on the life cycle of the bruchid seed feeder Kytorhinus sharpianus
Authors: Ishihara Michihiro
Published: October 2003

The voltinism of the bruchid Kytorhinus sharpianus Bridwell (Coleoptera: Bruchidae) and the phenology of its host plant Sophora flavescens Aiton (Leguminosae) were observed at four latitudes: Aomori (40°46′ N), Obanazawa (38°37′ N), Kujiranami (37°21′ N) and Mitsuma (36°05′ N) in northeastern Honshu (Japan). Kytorhinus sharpianus life cycle ranged from bivoltine and partially trivoltine in the south to univoltine and partially bivoltine in the north. Sophora flavescens started growing later in spring at higher latitudes. However, the relative growth rate was higher in the north (Aomori) than in the south (Mitsuma). In parallel with this, the first‐generation of adult K. sharpianus appeared later at higher latitudes. When the four local populations were reared at 24 °C, L16:D8 and 65% r.h., males developed faster than females. The mean developmental time showed a saw‐toothed latitudinal cline. The reversion in the latitudinal trend of variation corresponded to the change in the major type of life cycles from univoltine to bivoltine. Two heat units throughout the year and post‐fruiting period were calculated as the sums of degree‐days above the developmental threshold (12 °C) of K. sharpianus. Both heat units decreased in parallel with each other with increasing latitude. The greater growth rate of hosts in the northern population compensated for the smaller heat units. In addition, when the heat units were divided by the degree‐days needed to complete development, the numerical value was the approximate number of generations observed in each locality.
Olfactory and gustatory behaviour by larvae of Lobesia botrana in response to Botrytis cinerea
Authors: Mondy N. , Pracros P. , Fermaud M. , Corio‐Costet M.‐F.
Published: October 2003

In vineyards, larvae of Lobesia botrana (Denis and Schiffermüller) (Lepidoptera: Tortricidae) and Botrytis cinerea (Persoon: Fries) often occur together. This study was carried out to establish whether first instar larvae are attracted by the fungus. Olfactory and gustatory responses of larvae to the fungus were investigated on grape berry clusters (Vitis vinifera) and in two types of olfactometer. In clusters infected partly by B. cinerea, 82% of first instar larvae settled where berries had been infected. In the olfactometers, first instar larvae detected and discriminated between two tested foods. They significantly preferred synthetic media or grape berries (cv., ‘Alphonse Lavallée’ or ‘Cabernet Sauvignon‘) infected with B. cinerea to non‐infected controls. The olfactory response led to 62.2% to 72.6% of the first instar larvae attracted by the fungus and the association of olfactory with gustatory responses resulted in similar rates (64.1% to 81.6%). So, the larvae were most attracted by synthetic media or grape berries infected by the fungus as compared to the controls. Olfaction appears to be the main sense involved in this attraction process.
Distinct feeding behavior between sexes of Frankliniella occidentalis results in higher scar production and lower tospovirus transmission by females
Authors: van, de Wetering F. , Hulshof J. , Posthuma K. , Harrewijn P. , Goldbach R. , Peters D.
Published: October 2003

Feeding behavior and scar production of male and female F. occidentalis (Pergande) (Thysanoptera: Thripidae) were studied in relation to transmission of tomato spotted wilt tospovirus (TSWV). Electrical penetration graph (EPG) analysis showed that females feed more frequently and intensively than males. The feeding intensity, reflected by silvery scar production and studied by an image analysis system, demonstrated that females induced more numerous scars than males. At the same time, males transmitted TSWV with a higher efficiency than females, indicating that TSWV transmission and scar production are not positively correlated. Furthermore, males produced significantly more local lesions of TSWV than females. These quantitative differences in scar production and transmission of TSWV can be explained by the lower mobility and higher consumption rate of females. The influence of the sex‐ratio on crop damage and virus transmission, and thus to the spread of TSWV, is emphasized.
Greenhouse and field evaluations of transgenic canola against diamondback moth, Plutella xylostella, and corn earworm, Helicoverpa zea
Authors: Ramachandran Suresh , Buntin G. David , All John N. , Raymer Paul L. , Stewart C. Neal
Published: October 2003

Canola (Brassica napus L.) cultivars Oscar and Westar, engineered with a Bacillus thuringiensis (Bt) cryIA(c) gene, were evaluated for resistance to lepidopterous pests, diamondback moth, Plutella xylostella L. (Plutellidae) and corn earworm, Helicoverpa zea (Boddie) (Noctuidae) in greenhouse and field conditions. In greenhouse preference assays conducted at vegetative and flowering plant stages, transgenic plants recorded very low levels of damage. A 100% diamondback moth mortality and ≈90% corn earworm mortality were obtained on transgenic plants in greenhouse antibiosis assays. The surviving corn earworm larvae on transgenic plants had reduced head capsule width and body weight. Mortality of diamondback moth and corn earworm were 100% and ≈95%, respectively, at different growth stages (seedling, vegetative, bolting, and flowering) on the transgenic plants in greenhouse tests. In field tests conducted during 1995–1997, plots were artificially infested with neonates of diamondback moth or corn earworm or left for natural infestation. Transgenic plants in all the treatments were highly resistant to diamondback moth and corn earworm larvae and had very low levels of defoliation. Plots infested with diamondback moth larvae had greater damage in both seasons as compared with corn earworm infested plots and plots under natural infestation. After exposure to defoliators, transgenic plants usually had higher final plant stand and produced more pods and seeds than non‐transgenic plants. Diamondback moth injury caused the most pronounced difference in plant stand and pod and seed number between transgenic and non‐transgenic plants. Our results suggest that transgenic canola could be used for effective management of diamondback moth and corn earworm on canola.
Melon aphid performance on chrysanthemum as mediated by cultivar, and differential levels of fertilization and irrigation
Authors: Bethke James A. , Redak Richard A. , Schuch Ursula K.
Published: October 2003

Population parameters of the melon aphid, Aphis gossypii Glover, were compared for insects grown on six cultivars of chrysanthemum, Dendranthema grandiflora Tzvelev (‘Fontana’, ‘Iridon’, ‘Pink Lady’, ‘Splendor’, ‘White Diamond’, and ‘White View Time’) fertilized with 3 different levels of nitrogen (80, 160 and 240 mg N/l) and 2 levels of irrigation (high 300 ml and low 210 ml every other day). Fecundity, longevity, and survivorship of aphids were significantly affected by the cultivar treatment, but were not affected by irrigation or fertilizer treatments or by any combination of interactions among cultivar, fertilizer and irrigation. Significantly fewer aphids survived on the cultivar ‘Pink Lady’ (populations reduced by 20.8%) than any other cultivar examined. Intrinsic rates of increase (rm), finite rates of increase (R0), and population doubling times (DT) for aphids were different among fertilizer levels and cultivars, but were not different among irrigation levels. There were no significant fertilizer by irrigation interaction effects upon rm, R0, or DT. The highest rate of fertilizer applied (240 mg N/liter) adversely affected the intrinsic rate of increase of melon aphids; however, aphid intrinsic rate of increase was weakly correlated with foliar soluble protein levels (r= 0.989, P = 0.0954). Foliar soluble protein levels were not associated with fertilization treatment. Melon aphids perform consistently better on the cultivars ‘White Diamond’, ‘Fontana’, and ‘Splendor’, relative to those aphids growing on ‘Iridon’, ‘Pink Lady’, or ‘White View Time’. In general, melon aphids performed best on ‘White Diamond’ and poorest on ‘Pink Lady’.
Probing and feeding characteristics of the greenhouse whitefly in association with host‐plant acceptance and whitefly strains
Authors: Lei H. , Tjallingii W. F. , van Lenteren J. C.
Published: October 2003

Host‐plant and whitefly strain effects and their interactions on the probing and sap feeding of the greenhouse whitefly, Trialeurodes vaporariorum (Westwood), have been investigated in this study using the DC‐EPG (Electrical Penetration Graph) technique. Whiteflies generally displayed fewer but longer probes on highly acceptable cucumber than on less acceptable tomato. Both whitefly strains, the T(omato)‐strain and the C(ucumber)‐strain, showed a significantly lower number of phloem phases on cucumber than on tomato. However, the duration of total phloem phases achieved by either of the whitefly strains on these two host plants was not significantly different. These data indicate that a more continuous phloem feeding has occurred on cucumber plants. Indeed, the percentage of phloem feeding time after the first sustained phloem phase (longer than 15 min) was higher on cucumber for the C‐strain whiteflies. When comparing these two whitefly strains, the T‐strain whiteflies probed less frequently but longer than the C‐strain whiteflies did on both host plants. Also, the T‐strain whiteflies displayed a longer duration of total phloem phases on tomato. An interaction between the whitefly strain and plant effects was detected on a parameter, which showed that whiteflies probed significantly longer before reaching the first phloem phase on the host plants that had been previously experienced. In conclusion, both plant species and whitefly strains affect whitefly's probing and feeding behaviour, though plant effects are much stronger.
Response of five insect herbivores to multiple allelochemicals under fluctuating temperatures
Authors: Stamp Nancy E. , Osier Tod L.
Published: October 2003

Analysis of the combined effects of allelochemicals on insect herbivores is useful because there may be adverse additive or even synergistic effects. Analysis of the simultaneous effects of temperature and alleochemicals is also necessary because these factors may interact. We examined the effects of three allelochemicals found in tomato (chlorogenic acid, rutin and tomatine) and thermal regime (21:10 °C and 26:15 °C, representing spring and summer respectively) on five insect herbivores (a Solanaceae specialist, Manduca sexta, and the polyphagous Heliothis virescens, Pseudoplusia includens, Spodoptera frugiperda and Trichoplusia ni). There were allelochemical interactions and thermal regime‐allelochemical interactions for all species, and so the patterns were complex. In some cases, paired allelochemicals or the combination of three allelochemicals showed adverse additive effects on insect performance. But that was not always the case, and there were only a few examples of synergism. Negative effects of the allelochemicals were sometimes, but not always, damped by the cooler thermal regime. Comparing the growth rates of the five species in this study with those of a previous study (a total of seven species) revealed five patterns. For two of three pairs of closely‐related species, the paired species had distinctly different patterns. For example, for H. virescens, tomatine prevented development and chlorogenic acid slowed growth, whereas for Helicoverpa zea, tomatine just slowed growth and the phenolics had little effect. The specialist Manduca sexta had a pattern that was midway between patterns of the generalists; it was not the most tolerant of the allelochemicals.
Response to orphaning in two Neotropical termites: Armitermes euamignathus and Embiratermes festivellus
Authors: Costa‐Leonardo Ana Maria , Soares Helena Xavier , Barsotti Raquel Cristina
Published: October 2003

In this paper we examine the potential of the termites Armitermes euamignathus Silvestri: 1901 and Embiratermes festivellus (Silvestri, 1901) (Isoptera, Termitidae, Nasutitermitinae) to produce neotenics experimentally. Three nests of the mound‐building termite A. euamignathus, from the Brazilian cerrado, had their primary queens removed in August 1994. After 12 months, only one mound survived; it had a normal appearance. In this healthy, orphaned colony we found the primary king, six physogastric nymphoid female replacement reproductives, two ergatoid female replacement reproductives, 46 nymphs, several presoldiers, soldiers, workers, larvae and many eggs. These data show that neotenics in A. euamignathus may originate from both workers and nymphs, but nymphoids are produced in larger numbers. The biometric study of nymphs and nymphoids suggests that these brachypterous neotenics were derived from third instar nymphs after a single moult or from four instar nymphs after a reduction of wing bud length. A piece of an E. festivellus nest with some third instar nymphs, soldiers and workers was kept under laboratory conditions. After 12 months, the whole experimental subcolony was examined and appeared to contain two pigmented nymphoid females, two pigmented nymphoid males, only one larva, seven nymphs of the same instar, 148 workers, five soldiers and many eggs. These results also indicate the capacity of the termite E. festivellus to produce nymphoid neotenics. These neotenic females were laying eggs, but they were not physogastric after a year, unlike some nymphoids of the same species collected from natural colonies.
The involvement of acetylcholinesterase in resistance of the California red scale Aonidiella aurantii to organophosphorus pesticides
Authors: Levitin Emanuel , Cohen Ephraim
Published: October 2003

Laboratory toxicity bioassays using chlorpyrifos (Dursban) confirmed the notion that development of resistance is responsible for widespread failures to control the California red scale, Aonidiella aurantii (Mask.) by applying organophosphorus (OP) compounds in citrus groves in Israel. Higher Vmax values of acetylcholinesterase (AChE) activity (9–13 fold) were measured in resistant strains collected from the field as compared to a susceptible line. No differences were found with respect to Km values using acetylthiocholine iodide as a substrate, or degree of inhibition (expressed by IC50 values) by the OP compounds chlorpyrifos‐oxon and paraoxon and the carbamate pirimicarb. We suggest that resistance of the California red scale is caused by excess of AChE molecules able to bind and thus scavenge inhibitory OP compounds. This scavenging mechanism related to AChE may be similar in other insect species where elevated levels of detoxifying esterases were implicated in conferring OP resistance.
Optimal timing of the production of sexuals in bumblebee colonies
Authors: Beekman M. , Lingeman R. , Kleijne F. M. , Sabelis M. W.
Published: October 2003

Colonies of annual eusocial insects often produce only workers until they switch to the production of sexuals (queens and males). This switch from the ergonomic phase to the reproductive phase has been modelled by Macevicz & Oster (1976). Their model predicts that the production of sexuals should take place approximately one generation (one brood developmental period) before resources are depleted in order to maximise the number of sexuals. Bumblebees, however, produce sexuals early (relative to colony lifetime) when resources are still abundant and thus the model of Macevicz & Oster does not hold for these insects.

Here we show that Macevicz & Oster's prediction hinges critically on their assumption that the egg laying rate of the queen is a function of the foraging effort of the workers. This assumption does not hold for bumblebees, where queens lay eggs at a constant rate. Taking this feature of bumblebees into account the model predicts early production of sexuals, since it does not pay to produce more workers and collect more resources than needed to raise sexuals.
Generation specific life history traits of winged Sitobion avenae
Authors: Helden A. J. , Dixon A. F. G.
Published: October 2003

When reared under constant conditions from egg hatch the proportion of offspring of Sitobion avenae (F.) (Aphididae: Macrosiphini) that developed into winged individuals declined from the second to fourth generation. The winged individuals produced in these three generations showed a progressive decrease in their wet and dry weights and an increase in the length of their largest embryo with generation. The trend in winged individual production and also the trends in their size and reproductive strategy appear to be programmed and are similar to the generation specific strategies that have been described in other species of aphid.
Performance and seasonal abundance of the neotropical brown stink bug, Euschistus heros nymphs and adults on a novel food plant (pigeonpea) and soybean
Authors: Panizzi Antônio R. , Oliveira Émerson D. M.
Published: October 2003

Pigeonpea, Cajanus cajan (L.) Millsp. (Leguminosae) was found as a novel food plant of the neotropical brown stink bug, Euschistus heros (F.), in Paraná State, Brazil. Laboratory studies indicated nymphs performing better when fed on immature pods of soybean, Glycine max (L.) Merrill (Leguminosae), than on immature pods of pigeonpea. Female nymphs required 1.7 d less to complete development and tended to have a lower mortality on soybean (17.5%) than on pigeonpea (25.0%). At emergence, fresh body weight was greater on soybean than on pigeonpea. Adult E. heros performed better on soybean than on pigeonpea. After 120 d, ≈35% of adults were alive on soybean and 30% on pigeonpea; 93.3% of females oviposited on soybean, and 73.3% on pigeonpea, with an oviposition delay of ≈17 days on pigeonpea compared to soybean. Fecundity was ≈63% greater on soybean than on pigeonpea, and adult body weight gain for females and males at different ages was ≈6–36% greater on soybean than on pigeonpea. E. heros colonized soybean during January–March, from the pod‐setting and filling stages (R3–R6) to maturity (R7–R8), and pigeonpea during April–June. These results indicate that E. heros has expanded its host range to pigeonpea in Brazil; pods of this plant are suitable food, and can support the insect during autumn‐early winter, after soybean harvest, and before it enters into partial hibernation.
The cowpea aphid, Aphis craccivora, host plant odours and pheromones
Authors: Pettersson J. , Karunaratne S. , Ahmed E. , Kumar V.
Published: October 2003

Olfactometer experiments were conducted with apterae and alatae of the cowpea aphid, Aphis craccivora, Koch (Hom.:Aphidoidea). The occurrence of density dependent related pheromones and odour response to their host plant Vigna unguiculata was studied. Apterae responded with positive anemotaxis to air passed over both small groups of apterae and alatae (≤10 individuals) but negatively to air that passed over a bigger group (≥20 individuals). Alatae responded in the same way to groups of apterae but were repelled by alatae independent of the size of the group applied as odour source in the olfactometer, except when exposed to air passing ten alatae feeding on cowpea leaves. This may be due to interaction between aphid pheromones and host plant odour. Both apterae and alatae showed a general attraction to green plants and were also able to distinguish between other host plants and cowpea, which was the original host of the aphid clone used in the experiments. When attacked by aphids, the cowpea plant responded with a temporal increase in attractivity that reached a maximum after 48 h and had disappeared after one week.
Monitoring spruce web‐spinning sawflies Cephalcia spp.: the correlation between trap catches and soil sampling
Authors: Battisti A. , Rodeghiero M.
Published: October 2003

The web‐spinning sawflies of the genus Cephalcia Panzer (Hymenoptera, Pamphiliidae) are usually monitored by sampling prepupae in soil and by catching adults with visual traps, including yellow sticky traps. However, adult catches have never been compared with the actual density of prepupae. In this paper, a relationship is presented between the catches of Cephalcia arvensis Panzer adults (mostly males) and the number of prepupae ready to emerge (pronymphs) in an outbreak area of spruce forest (Picea abies Karsten) in the Southern Alps (Asiago, Italy). A significant linear relationship between the logarithmic estimates of the two variables was found. The model includes a spatial autoregressive parameter because adult catches were spatially correlated. The relationship allows to know whether or not the defoliation threshold of 20 pronymphs/m2 in spring samples is being exceeded, based on the number of adults caught on yellow sticky traps (defoliation threshold of 14.26 adults/trap). The variance not explained by the model is probably due to the flight behaviour of adult males, to the low precision of the estimated pronymph density at low population levels, and to the attraction of males by few females that are trapped and remain alive. The model was validated in a large monitoring programme of undamaged alpine spruce forests and allowed detection of two newly infested stands out of six that were considered at risk of defoliation, because of adult catch exceeded the threshold. Low adult catches were always associated with absence of defoliation. Our conclusion is that trapping of adult sawflies is a cheaper and easier monitoring method than prepupae sampling in the soil. This makes earlier detection of outbreaks possible, and consequently more efficient control.
Comparative histopathology of some Diptera and Crustacea of aquatic alpine ecosystems, after treatment with Bacillus thuringiensis var. israelensis
Authors: Rey D. , Long A. , Pautou M.P. , Meyran J.C.
Published: October 2003

Species of Diptera (larval Culicidae, Chironomidae and Simuliidae) and Crustacea (cladoceran adults) that are representative of the fauna of aquatic alpine ecosystems are routinely treated with Bacillus thuringiensis var. israelensis (Bti) for mosquito control. The toxicity of Bti on these organisms was investigated. Bioassays indicated that Bti used at the concentration for operational field application is deleterious to all dipteran species, but not to Cladocera. Histopathological observations reveal that, in all cases, the midgut epithelium is affected by Bti treatment. However, the vulnerability of epithelial cells to the microbial insecticide is different from one cell‐type to another, clear cells being more vulnerable than dark cells. Because of the concentration of clear cells within the anterior midgut of dipteran larvae, this region appears to be the first to show symptoms of intoxication through enhancing a natural process of cell turnover. The relative importance of such a vulnerable region in the midgut of dipteran larvae may account for the general efficacy of Bti to these species. Its harmlessness to Cladocera may be correlated to the relative scarcity of clear cells and their patchy distribution along the whole midgut together with important cellular renewal capacity of the epithelium.
Characterization of digestive proteases in the weevil Aubeonymus mariaefranciscae and effects of proteinase inhibitors on larval development and survival
Authors: Ortego F. , Farinós G.P. , Ruíz M. , Marco V. , Castañera P.
Published: October 2003

The major digestive proteinase activities of a new sugar beet pest, Aubeonymus mariaefranciscae Roudier (Coleoptera: Curculionidae), were characterized. Both larvae and adults of A. mariaefranciscae were found to use a complex proteolytic system for protein digestion based on at least trypsin‐, chymotrypsin‐, elastase‐, cathepsin D, leucine aminopeptidase‐, carboxypeptidase A‐ and carboxypeptidase B‐like activities. An azocaseinolytic activity at pH 5.0–7.0 was identified, that was not affected by specific inhibitors and activators, making its classification in any of the mechanistic classes established not possible. According to this proteolytic profile, several serine proteinase inhibitors were tested in vitro and in vivo to establish their potential as resistance factors against A. mariaefranciscae. Larvae fed from neonate to pupation on diets containing 0.2% (w/w) soybean Bowman‐Birk trypsin‐chymotrypsin inhibitor, soybean Kunitz trypsin inhibitor, turkey egg white trypsin inhibitor, or lima bean trypsin inhibitor endure lower survival rates and display significant delays in the developmental time to pupation and to adult emergence. Interestingly, the most significant levels of mortality (about 90%) occurred with larvae fed on diets containing a combination of two or three inhibitors, suggesting a synergistic toxicity.
Antifeedant effects of sublethal dosages of imidacloprid on Bemisia tabaci
Authors: Nauen Ralf , Koob Birgit , Elbert Alfred
Published: October 2003

The effects of sublethal dosages of the chloronicotinyl insecticide imidacloprid on different strains of the tobacco whitefly, Bemisia tabaci Gennadius (Homoptera: Aleyrodidae), have been studied after leaf dip and systemic application. All bioassays were performed with the insecticide susceptible strain, SUD‐S, and two Spanish biotypes, ALM‐2 and LMPA‐2, both resistant to conventional insecticides and with a lower susceptibility towards imidacloprid. Honeydew, excreted by all strains feeding on treated and untreated cotton leaf discs was quantified by photometric analysis of its carbohydrate content. EC50‐values for the depression of honeydew excretion in female adults after systemic application of imidacloprid were calculated at 0.037 ppm, 0.027 ppm and 0.048 ppm for strains SUD‐S, ALM‐2 and LMPA‐2, respectively, indicating no significant differences between strains in feeding behaviour throughout an 48 h testing period. Depending on the strain these EC50‐values were 150‐ to 850‐times lower than LC50‐values calculated for mortality in the same bioassay. Starvation tests revealed mean survival times of >48 h for female adults placed on agar without leaf discs, indicating that sublethal dosages of imidacloprid which caused antifeedant responses, were probably not covered in common 48 h systemic bioassays, used to monitor resistance to imidacloprid. Effects of sublethal dosages on honeydew excretion after leaf dip application seem to be minor. In choice situations with systemically treated and untreated leaf discs in a single container, female adults of B. tabaci showed a clear preference for the untreated leaf discs. However, when using leaf discs treated by painting the surface with imidacloprid in the same bioassay, feeding activities on treated and untreated leaf discs were not significantly different. The results of the present study demonstrate the antifeedant properties of imidacloprid on B. tabaci, which might play an essential role after soil application or seed treatment under field conditions.
Change in foraging behaviour of the predatory mite Phytoseiulus persimilis after exposure to dead conspecifics and their products
Authors: Schütte Conny , van Baarlen Peter , Dijkman Herman , Dicke Marcel
Published: October 2003

Adult females of the predatory mite Phytoseiulus persimilis Athias‐Henriot are strongly attracted to infochemicals released by plants infested with their prey, the two‐spotted spider mite (Tetranychus urticae Koch), thereby effectively locating their prey. However, we found a consistently lower degree of attraction to these infochemicals for a population of P. persimilis, which is called non‐responding population. Here we demonstrate that this low degree of attraction is a contagious phenomenon and that it cannot be explained by differences in abiotic conditions, physiological state and experience of predators or by genetic differences between predator populations. Female predators exposed to dead conspecifics of the non‐responding population and their products showed a lower degree of attraction to plant odours and a higher mortality than predators exposed to products of a living conspecific of the non‐responding population. This was true 6–7 days after contact with dead conspecifics and their products whereas 2 days after contact no effects were detected. The present results are discussed in view of our hypothesis that the change in foraging behaviour as well as the high mortality rate are symptoms of a contagious disease affecting the non‐responding population.
Behaviour of pink bollworm males near high‐dose, point sources of pheromone in field wind tunnels: insights into mechanisms of mating disruption
Authors: Cardé Ring T. , Staten Robert T. , Mafra‐Neto Agenor
Published: October 2003

The mechanisms by which the application of formulated pheromone interferes with mating in the pink bollworm moth (PBW), Pectinophora gossypiella were examined in 0.4 ha cotton fields using high‐dose (78 mg A.I.) sealed polyethylene dispensers. Walk‐in, field wind tunnels 6.2 m long were placed over two rows of cotton. Treatments consisted of a control, a tunnel in a field free of disruptant formulation; a 3‐rope treatment, in which the field was free of pheromone but one of the cotton rows in the wind tunnel was treated with 3 PBW ropes; and a rope‐grid treatment, in which the field was treated with PBW ropes at the standard density of 1000 ha−1 and one of the cotton rows inside the wind tunnel was treated with 3 PBW ropes. We released marked males into the tunnels near sunset or held them in field cages for 24 h prior to assay. Two pheromone traps at the tunnel's upwind end monitored the ability of males to locate point sources of pheromone. In the 3‐rope tunnel, traps placed upwind of the cotton row treated with disruptant pheromone captured far fewer males than those placed upwind of the untreated cotton row. In the tunnel situated in the centre of the rope‐gridded field, very few males were caught in traps in both rows, indicating a camouflage of the pheromone plumes from the traps by the background of airborne disruptant drawn into the tunnel from the field. Activity of moths near the synthetic pheromone sources was video‐recorded. Males oriented to, landed on or near, and walked on or near, PBW ropes, indicating competition between pheromone sources as a mechanism of mating disruption. Most males visiting PBW ropes became quiescent or disappeared from the field of view after a few minutes, suggesting a habituation/adaptation of response. The rhythm of attraction of males held in the field for 24 h before release was comprised of a small peak of activity near 2000 h, with the majority of attraction between 2300 and 0300 h. Much of the attraction before 0100 appears to be an advancement of the male's normal diel rhythm, caused by the presence of disruptant. Together these findings indicate that mating disruption of pink bollworm using the PBW ropes is achieved by a combination of mechanisms: a camouflage of natural plumes, competition between pheromone sources, habituation, and some advancement of the male's rhythm of response.
Rapid adaptation of squash bug, Anasa tristis, populations to a resistant cucurbit cultivar
Authors: Margolies David C. , Nechols James R. , Vogt Elizabeth A.
Published: October 2003

We conducted laboratory experiments on two field‐collected populations of the squash bug, [Anasa tristis (De Geer) (Hemiptera: Coreidae)], to compare their responses to five generations of selection on a resistant squash cultivar ‘Waltham Butternut’, a susceptible cultivar ‘Early Prolific Straightneck’, or alternating generations on the resistant and susceptible cultivars. Before testing, one population was maintained for 1 generation on susceptible squash plants, while the other was maintained on the same cultivar for 5 generations. In both populations, nymphal survival decreased markedly in the first generation on resistant squash, but then approximately doubled in the second generation reared on the resistant cultivar. By the end of the experiments, survival on the rearing host was the same for A. tristis maintained continuously on a single cultivar, regardless of which cultivar. Immediately following one or more generations on resistant plants, A. tristis nymphs had lower survival on the susceptible cultivar than did nymphs that had been maintained for consecutive generations on the susceptible cultivar. Results of reciprocal crosses between lines of A. tristis reared on either resistant or susceptible squash for five generations indicated a genetic basis for differences in nymphal survival on the two cultivars.

In contrast with the changes in nymphal survival, the preoviposition period became progressively longer when A. tristis was reared for several generations on the resistant cultivar compared to the susceptible one. Prior rearing on resistant plants increased the preoviposition period of adults placed on susceptible plants. However, adult feeding on resistant plants following nymphal development on susceptible plants did not result in an increase in the preoviposition period on resistant plants. Our findings indicate that squash bugs can adapt to resistant plants within a relatively short period in the laboratory. However, ecological and agricultural factors should prevent squash bugs from overcoming resistance in the field.