Host Plants Effect on Preference , Development and Reproduction of Plutella xylostella ( L . ) ( Lepidoptera : Plutellidae ) Under Laboratory Conditions

The diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae) is the most destructive and cosmopolitan pest on brassicaceous crops. In this study, the development and reproduction of diamondback moth were evaluated at 25 ± 1<C, 60 ± 5% RH and a photoperiod of 16L: 8D hours on five commonly growing rapeseed cultivars: Licord, Modena, Okapi, RGsoo3 and REGXkobra. The development times from egg to adult ranged from 15.05±0.26 days on Licord to 16.87±0.40 days on Modena and showed significant differences on various rapeseed cultivars. The shortest and longest adult longevity of P. xylostella were estimated to be 5.00 ± 0.31 and 10.02 ± 0.69 days on Modena and RGsoo3 cultivars, respectively. On average, there were 92.27 ± 16.40, 129.00 ± 16.46, 158.84 ± 17.48, 173.75 ± 20.25 and 242.73 ± 25.64 eggs produced per female on Okapi, Licord, Modena, REGXkobra and RGsoo3, respectively. The oviposition periods of P. xylostella were significantly different on various rapeseed cultivars and the highest oviposition period was obtained on RGsoo3. There were significant differences among mean number of deposited eggs on five rapeseed cultivars after 24, 48 and 72 hours in no-choice condition. While, in free-choice condition, the oviposition of diamondback moth were not significantly different among the rapeseed cultivars and during different times. Therefore several mechanisms could explain the difference in attractiveness of surfaces with varying wax content as oviposition sites for P. xylostella, including visual, chemical and tactile difference between substrates. These mechanisms are discussed. Key word: Diamondback moth, Plutella xylostella, rapeseed cultivars, reproduction, development Introduction The diamondback moth, Plutella xylostella (L.), is a serious pest of crucifer crop throughout the world [25]. The diamondback moth has become recognized worldwide because of its expanding distribution and capacity to rapidly evolve resistance to insecticides[20]. The diamondback moth occurs throughout the year wherever its host plants are grown. Diamondback moth larvae feed on all plants in the crucifer family (canola, Brassica campestris L. and Brassica napus L., mustard, Brassica juncea L.), cole crops (cabbage, Brassica oleracea L. subsp. capitata, cauliflower Brassica oleracea L. subsp. botrytis, and kohlrabi Brassica oleracea L. subsp gongylodes) and on several green house plants. Several studies have been conducted on many species of moth herbivores to explore the relationship between preferences of ovipositing female moths for certain host plants and the subsequent performance of their larvae on those hosts[12,18]. It was documented as early as the 1950s that adult female moths show preferences for various host species and for modules Corresponding Author: Ali Asghar Talebi, Department of Entomology, Faculty of Agriculture, Tarbiat Modares University, P. O. Box: 14115-336, Tehran, IRAN, E-mail: talebia@modares.ac. ir 109 Adv. Environ. Biol., 2(3): 108-114, 2008 within one host species [12]. Because of the widespread use of insecticides to control of P. xylostella, it has developed resistance to numerous insecticides, including several Bacillus thuringiensis (BT) products[24,23,25]. The emergence of insecticide resistance population has driven many studies and researches the development towards the development of alternative methods for its control [22]. This has led to a renewed interest in developing alternatives to the use of insecticides, such as biological control and development of resistant plants [26]. Plutella xylostella is likely attracted to its b r a s s i c a c e o u s h o s t p l a n t s b y c h e m i c a l (olfactory/gustatory) and physical (tactile/visual) stimuli[10,1,15,3]. Behaviors associated with host plant acceptance and oviposition comprises antennal rotation, antennation and ovipositor sweep[10]. Several mechanisms could explain the differences in attractiveness of surfaces with varying wax content as oviposition sites for P. xylostella, including visual, chemical, and tactile differences between substrates [11]. Brassica vegetable specially cabbage, B. oleracea subsp. capitata and cauliflower B. oleracea subsp. botrytis are important vegetable crops and cultivated in most parts of Tehran province of Iran. Plutella xylostella occurs annually throughout this province wherever brassicaceous crops are grown and causes substantial crop losses during outbreak years. It has been well documented that Lepidopteran females demonstra te significan t oviposition preferences between plant species and between cultivars of the same species[12,18,27]. However, when this work was conducted it was not known which cultivar of rapeseed preferred for oviposition under artificial rearing conditions. Consequently, the main objective of this study was to determine the effect of five rapeseed, Brassica napus L. , cultivars (Licord, Modena, Okapi, RGsoo3 and REGXkobra) on the development and reproduction of P. xylostella. Understanding these information will help in the development of a comprehensive IPM program for rapeseed. Material and Methods