Effects of intraguild predation on fitness components of coccinellid beetle Hippodamia variegate
عنوان دوره: دومین کنگره بین المللی حشره شناسی ایران
نویسندگان
چکیده
Aphis gossypii Glover (Hem.: Aphididae) is one of the most important pests of cucumber plants. In addition to the direct damage, several plant viruses, such as cucumber mosaic virus are transmitted by this pest. The coccinellid beetle Hippodamia variegata (Goez) and the parasitoid wasp Lysiphlebus fabarum (Marshall) (Braconidae: Aphidiinae), have an important role in reducing population of this pest. The simultaneous use of these biocontrol agents under an integrated pest management program may provide the possibility of intraguild predation. In this study, the larvae ladybird feeding on parasitized cotton aphids by L. fabarum and the possible effects of this feeding on biological indicators related to the efficiency of progenies ladybird were examined. All larval stages of treatment coccinellids were fed on parasitized aphids (72 hours previously parasitized), in contrast to control coccinellids which was fed on healthy aphids. In following, emerging male and female from similar treatment was coupled in a Petri dish (n=16 for both cases), while fed from healthy aphids. The embryonic developmental times of eggs laid on the third, sixth, ninth and twelfth days, and the head capsule width of first instar larvae, before the start of feeding, were measured. In following, developmental times of larval and pupal stages, and weight of emerging males and females were measured. All insects rearing and experiments were performed in growth chambers under 21 ± 1°C, 65–75% RH, and a 16:8 (L:D) photoperiod. The results showed that embryonic, larval and pupal developmental time of progenies were not significantly different, when their parents fed on the parasitized or healthy aphids, whereas the head capsule width of treated offspring were significantly larger than control offspring (F =25.8, df =1,301, P <0.001). Also the sex ratio of progenies (G =3.83, df =1,216, P =0.05) and their weight (male: F =5.73, df =1,94, P =0.01; female: F =4.98, df =1,86, P =0.02) were significantly increased when their parents fed on the parasitized aphids. Although wasp population decline due to intraguild predation is to be expected, however, the results show that intraguild predation can lead to gain fitness for offspring of ladybird, (i.e. larger body size, greater weight, and higher sex ratio). So it is expected that these ladybirds with increased features act as a better hunter in control of this pest.
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