Influence Of Visual,Olfactory And Contact Cues On Host Searching Behavior Of Cotesia Vestalis

Cotesia vestalis(Hymenoptera: Braconidae)is one of the most efficient bio-control enemies of the pest Plutella xylostella(Lepidoptera:Plutellidae).Some studies confirmed that,in long distance,olfactory cues such as plant volatiles play important roles for host orientation of C.vestalis.This parasitoid prefers volatiles from plant be fed by P.xylostella than which from intact plant.However,olfactory cues may not play similar important roles in short distance as in long distance.Because plant volatiles could be confused: P.xylostella evolved especial behavior to mix up plant volatiles and conceal itself.P.xylostella was showed could employ patch feed behavior to mix up the plant volatiles,it can also move from plant to plant in process of feed.Therefore,we assume C.vestalis may use other cues associate with the host P.xylostella in host searching behavior.In the study,series of different sensory cues(visual,olfatory and contact)were used to stimulated C.vestalis in the host forging process.Time of host searching behaviors after stimulate or without stimulate were both recorded.By investigating the learning and memory effects of C.vestalis after stimulate,we try to answer whether visual,olfatory and contact cues play role in host searching process of C.vestalis.The main results are as follows:1.Olfatory cues influence host searching behavior of C.vestalis.(1)Compare to odors from artificial food of P.xylostella,C.vestalis significant prefers odors from radish sprout(P < 0.01).Moreover,this preference did not change when C.vestalis was developed from P.xylostella larva which feed on artificial food.(2)When parasitized hosts in a surrounding of artificial odor(vanilla scent),C.vestalis showed searching behavior when supply with vanilla scent after interval time of0.5 h,6 h and 24 h.2.Visual cues did not effect on searching behavior of C.vestalis.(1)When supplied with different colors surroundings,C.vestalis prefer some colors from others in laboratory.Such as: prefers red to green,prefers blue to green,prefers yellow to red.(2)While,host searching behavior did not influenced due to colors surroundings.If C.vestalis parasitized hosts with red color surrounding,it continue searching host in the same color surrounding for(278.67 ± 21.47 s).Similar searching behavior(233.83 ± 12.46 s)were recorded when it placed in a different color surrounding(green).When colors above changed to blue and green,yellow and red,we got similar results.We considered that,visual cues such as environment colors did not influenced host searching behaviors of C.vestalis.3.Contact cues can influence C.vestalis’ s host searching behavior.When C.vestalis parasitized hosts on cotton,then placed it on new cotton,filter paper or plastic film respectively,it maintained different time of host searching behavior : cotton(570.00 ± 19.15 s),filter paper(345.67± 12.52 s),plastic film(0 s).When C.vestalis parasitized hosts on filter paper,it maintained longest host searching behavior on filter paper(459.67 ± 9.28 s)compare to cotton and plastic film.When C.vestalis parasitized hosts on plastic film,it maintained longest host searching behavior on plastic film(597.67 ± 2.33 s)compare to cotton and filter paper.We believed that,host searching behaviors of C.vestalis were significantly influenced by contact cues.4.Both olfactory and contact cues play roles on host searching behavior of C.vestalis.When C.vestalis parasitized hosts with vanilla scent(olfactory cues)and on filter paper(contact cues),it showed longest host searching behavior in same odor on filter paper maintain(587.16 ± 6.30 s).The wasp showed maintain(351.50 ± 11.09 s)of host searching behavior on filter paper and without vanilla scent supplied,showed maintain(182.83 ± 4.76 s)of host searching behavior with vanilla scent but without filter paper,and showed only(44.16 ± 1.90 s)of host searching behavior without both cues.We considered contact cues play more important role than olfactory cues in host searching process of C.vestalis.5.Scanning electron microscopy observation showed both male and female C.vestalis had lots of sensilla on femur and tarsi.Female wasp had more triochoid sensilla on both femur and tarsi than male.More sensilla were observed on female’s ovipositor than male’s volsellae.We assume that,more sensilla on female wasp may benefit C.vestalis,because contact cues play very important role in host searching behavior of this wasp.