Effects of the presence of predatory ladybird, Hippodamia variegate, feeding on Aphis gossypii on reproductive activity and olfactory response of Lysiphlebus fabarum
عنوان دوره: دومین کنگره بین المللی حشره شناسی ایران
نویسندگان
چکیده
The cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae) is a cosmopolitan, polyphagous, and a wide host range aphid species, which is known as an important pest of crops and ornamental plants in fields and greenhouses. The coccinellid beetle Hippodamia variegate and the parasitoid wasp Lysiphlebus fabarum (Braconidae: Aphidiinae) feed simultaneously on this aphid in natural conditions. The reproductive activity and olfactory response of L. fabarum (Intraguild prey) to the presence of H. variegate (Intraguild predator), was investigated on the cotton aphid on cucumber plants. In the first experiment, 45 experimental arenas (cucumber leaf disc in Petri dishes containing agar solution) were prepared and placed 15 adult aphids in each of those. 10 aphid carcasses were added into the first 15 arenas (first treatment). A saturated female ladybird was introduced into each second treatment arenas. In the control treatment, only adult aphids were present. In the following, a female wasp (2 days old and mated) was released in each of the experimental units. After two hours, wasps were removed and aphids reared to determine the reproductive characteristics of the parasitoid wasp (percent parasitism, percent emergence, and sex ratio). In the next experiment, the preference of the female wasps to these patches was determined using a Y-tube olfactometer. For this purpose, a female wasp (n=20) was placed in the release reservoir to choice one of two different host patches (first or second treatment against control treatment). All insects rearing and experiments were performed in growth chambers under 21 ± 1°C, 65–75% RH, and a 16:8 (L:D) photoperiod. Based on the results, the presence of female ladybird had a significant reducing effect on the percent parasitism by L. fabarum (G =6.99, df =2, 42, P =0.03). Also results showed that percent emergence and sex ratio was not significantly different in three food patches. According to olfactometer test results, the parasitoid wasp significantly avoided the patch containing the ladybird (χ2=6.40, df=19, P=0.01), but they could not identify the carcasses of aphids in the food patch. The reason that female wasps avoided the patch containing the ladybird may be due to the ability of wasps to identify volatile chemicals made of ladybirds. Indeed, wasps by avoiding these patches kept safe themselves and their progenies from intraguild predation. This result reflects the evolution of wasps to maximize their fitness and fitness of progenies.
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