Biodiversity of fruit fly Bactrocera spp. (Diptera : Tephritdae) in peninsular Thailand and population ecology of some species on guava Psidium guajava L.

The biodiversity of fruit fly Bactrocera spp. and the population ecology of two key factors species of these genera were carried out in peninsular Thailand on guava Psidium guajava (L.) during April 2011 and March 2013 at twelve sampling sites. The objectives of the research were to (1) elucidate and identify Bactrocera spp. infesting plants in the family myrtaceae, (2) determine the seasonality of B. carambolae and B. papayae on guava and, (3) construct cohort life tables of B. carambolae and B. papayae. Fruit fly specimens were collected from the field with the aid of (1) Steiner trap (Thailand modification) baited with a mixture of parapheromone (methyl eugenol Benzene,1,2,-dimethoxy-4-(2-propenyl) and pyrethriod (Changzhou Kangmei Chemical Industry, China) at the rate of 62.5 ml pyrethroid / 1,000 ml methyl eugenol, and (2) Ball trap AR934 (ISCA modified McPhail trap USA) baited with food substance (Torula yeast). Fruits were also sampled from P. guajava and other fruit bearing trees to the radius of approximately 1,500 meters. Adult flies were maintained in the laboratory at 25 ± 1 o C, 75 ± 5% relative humidity (RH) and photoperiod of L12:D12 for life history strategy study. The sum of 226,658 specimens of 33 species belonging to two genera; Bactrocera and Dacus were collected from the field across southern Thailand during the biodiversity study. Sampling of fruit flies was conducted in four provinces with Steiner and Ball traps, respectively. One commercial guava orchard located in agroforested area was selected at each province. Each of the trap was replicated twice on the orchards and it surroundings. From this study, the genus Bactrocera had the highest number of 31 species of which 8 species were common to all sites among which B. papayae and B. carambolae were the most abundant, hence, key factor species occurring in large numbers across southern Thailand. From the Bactrocera spp. , 14, including a taxon (B. sp1) were new records in this region and were found to be localized occurring mostly at provinces adjacent to peninsular Malaysia. The biodiversity pattern was analyzed for richness, evenness and similarity of sites and two associations were elucidated viz; (1) provinces adjacent to peninsular Malaysia were the richest in species, and (2) provinces towards the hinterland were less rich in species number. Similarity of sites also followed the aforementioned groupings. The most probable reasons for the differential biodiversity patterns could be link to the cross infestation from neighbouring countries, forest type, vegetation cover, availability of host plants and the average weather conditions prevailing at each province. Seasonality of the key factor species; B. carambolae and B. papayae was studied for 53 consecutive weeks in guava orchards and surrounding environments in southern Thailand. The fruit flies were collected by using Steiner traps baited with methyl eugenol as an attractant only. Guava fruits were sampled and categorized into three developmental stages as ripe, mature and immature with the aid of fruit firmness tester. Both species were trapped in the field throughout the season and exhibited distinct patterns of seasonal occurrence with two population peaks, August-September and May for B. papayae and protracted irregular pattern of occurrence for B. carambolae. The density was almost always greater for B. papayae than for B. carambolae at all the study sites. The population density was affected to some extent by the interaction of temperature, rainfall and relative humidity. The fruit sampling revealed that both fruit fly species emerged in large numbers from ripe guava fruits than for any other of the developmental stages. High fecundity, gregariousness, ability to colonise and invade new environment could be responsible for large population occurrence of B. papayae. The life history strategy of the pre-imaginal stages of B. carambolae and B. papayae were compared at six constant temperatures of 15, 20, 25, 27, 30 and 35 o C, 70±5 RH and at photoperiod of L12:D12. The objective was to determine the effect of temperature on the developmental stages for optimizing rearing and to understand their geographical pattern of occurrence. A strong and positive linear relationship was observed between temperature and developmental rate of immature stages of B. carambolae, correlation coefficient (R 2 ) = 0.99, 0.95 and 0.99 for egg, larva and pupa, respectively. Similarly, a strong and positive linear relationship was observed between temperature and developmental rate of B. papayae, R 2 = 0.98, 0.91 and 0.99 for egg, larva and pupa, respectively. B. carambolae was found to exhibit high threshold temperature and consequently, high degree days when compared to B. papayae. A temperature summation model was used to estimate lower threshold temperature and thermal constant. The lowest threshold temperatures for B. carambolae and B. papayae were 12.4, 11.2 and 11.6 o C; and 12.1, 10.5 and 10.9 o C for eggs, larvae and pupa, respectively. The thermal constants for total development of B. carambolae and B. papayae were 371.4 and 330.1 degree-days respectively. B. papayae was significantly faster in development and higher in survival, and appeared to be better adapted to low temperatures than B. carambolae as it exhibited lowest threshold temperatures at all immature stages. The observed differences in response to various temperatures revealed to some extent the impact of temperature on their distribution in peninsular Thailand and other parts of the world. The discrepancies observed in hatching time between the eggs of both species at specific constant temperature, led to the examination of the latter by using Olympus microscope with inbuilt ocular micrometer for morphometric study, Olympus DP72 Universal Camera microscope to capture the image of the eggs and Scanning Electron Microscope (SEM) was used for the detailed morphological studies. None of the eggs of the studied species had conspicuous respiratory appendage. The eggs are similar in gross morphology, tapering towards the anterior and posterior poles. Presence of papilla, mycropyle and aeropyles are peculiar to both species but with some variations. The papilla and mycropyle with clumsy woolly structure was common to B. carambolae. But the aeropyles on the chorion of B. papayae were numerous and in variable diameters. The diagnostic characters to differentiate between these two species include the chorion ornamentation, location of aeropyles and rim of chorion. Life table of B. carambolae and B. papayae were compared at constant temperatures of 20, 25, 27 and 30 ± 1 o C, 70 ± 5% relative humidity (RH) and photoperiod of L12:D12. The “intermediate optimum temperature” fall in the range of 25-27 o C. Fly populations declined rapidly towards extreme temperatures (cold or hotness). All population and reproductive parameters analysed revealed that B. papayae survived better than B. carambolae. Male flies of both species were also found to live longer and had high life expectancy than their female cohort members. The study suggested that B. papayae can invade and colonise a new area faster than other species in this region. This may be the reason behind it more prevalence and abundance in field over other Bactrocera spp. Therefore, B. carambolae and B. papayae should be considered as notorious pests that could threaten the growth of horticultural industry and have an immense impact on the fruit fly fauna in southern Thailand.