Functional Response Studies Of Parasitoid Aphidius Gifuensis(Hymenoptera: Braconidae)Against Green Peach Aphid Myzus Persicae(Hemiptera: Aphididae) In Sweet Pepper Plant

Green peach aphid, Myzus persicae(Sulzer)(Hemiptera: Aphididae) is a principal pest of vegetables and crops. It has more than 875 secondary host plants and also vector of more than 100 plant viruses. To protect crops from this dangerous pest, mostly chemical control methods were used but chemical control causes many health problems for humans and environmental issues. Therefore we used biological control methods for aphids in present study. In biological control, there are many natural enemies for example Predators, Parasitoids,Fungus and Viruses but in present study we focus on parasitoid Aphidius gifuensis(Ashmead)(Hymenoptera: Braconidae). A. gifuensis is an important parasitoid of aphids found especially in China and Japan. In selection of good bio control agent there are many attributes to consider for natural enemy. Among them, functional response of parasitoid is very important attribute. Functional response is basically behavior of parasitoid of parasitizing prey in increasing densities of prey. Functional responses are of three types I, II and III. In Type I,there is linear increase in parasitizing of prey. In type II there is hyperbolic increase in parasitizing of prey. In type III functional response there is sigmoidal increase in parasitizing of prey. So these are three types of behaviors and we want to know that when parasitoid display type I, II or III functional response and what factors affect in switching functional response from one type to other. So it is interesting study in understanding the behavior and ecology of parasitoid. We in this study evaluated three factors: Temperature, Plant canopy and Cage size. We evaluated the effect of these three factors on functional response of A. gifuensis parasitizing M. persicae. In many earlier studies scientists commonly used petri dishes for experiments but in this study we used sweet pepper whole plant that is planted in pots to better understand it and it is something new as compared to previous studies and more open environment. In present study, First experiment considers effects of temperatures on functional response. We tested four temperatures 15°C, 20°C, 25°C and 30°C. Results indicated that A. gifuensis in all temperatures display type II functional response. Attack rates(a) were higher at 20°C and 25°C. The lowest attack rates(a) were at 15°C and 30°C.Similarly handling times(Th) was lowest at 20°C and highest at 30°C. This indicates that A.gifuensis performs best in parasitizing aphids at temperature from 20°C to 25°C. In second experiment we take effect of plant canopy on functional response of A. gifuensis against M.persicae. We take four plant canopies of sweet pepper plant(6, 10, 14 and 18 leaves). Results indicated that A. gifuensis in all plant stages display type II functional response however there is differences in attack rates(a) and handling times(Th) at different plant canopies. At 6leaves plant canopy, attack rate(a) of A. gifuensis was higher and handling time(Th) was lower. At 18 leaves plant canopy, attack rate(a) of A. gifuensiss was lower and handling time(Th) was higher. This indicates that plant canopy also effect on functional response because when plant canopy was small it means that area of finding prey was smaller and attack rates(a) are high but when plant canopy was big than area of finding prey was larger and attack rate is lower. In our Third experiment we take effect of cage size on functional response of A.gifuensis against M. persicae. We take four cage sizes(30×30×30cm, 60×60×60cm,90×90×90cm, 120×120×120×120cm). In this experiment results are very different from other experiments. At cage size(30×30×30cm) functional response is of type II but at other cages sizes(60×60×60cm, 90×90×90cm, 120×120×120cm) functional responses are of type III.This was might be due to that at small searching area A. gifuensis display type II but when searching area is big then there is clear difference in functional response and it switches from type II to type III. Parasitism in small cage is higher and in large cages is lower. These results will be helpful in understanding functional response theory and how other factors can change functional response type. This study will be helpful for sweet pepper growers who want to use A. gifuensis in biological control programs in greenhouses and fields.