The Study On Chemosensory Function Of Three Phytoseiid Mites In The Process Of Prey Recognition

Phytoseiid mites are important biological control agents and many of its species have effective control effects on small sap-sucking pests in agriculture and horticulture,such as spider mites,thrips and whiteflies.According to their feeding habits,Phytoseiulus persimilis,Neoseiulus californicus and Amblyseius swirskii belong to specialized mite predators,selective predators of tetranychid mites and generalist predators.In addition,their feeding behavior is significantly affected by their previous feeding experience.However,the influence of early feeding experience on prey selection of predator mites is still unclear when different preys coexist in the same plant.Thus,in order to figure out the effect of the early feeding experience of these predators on prey selection of adult mites,our study compared the number of preys selected firstly by adult females of N.californicus and A.swirskii after early feeding experience.Meanwhile,in order to find the reasons for the differences in prey recognition of predator mites belonging to different types of predators,this study also explored the differences in the chemosensilla and chemosensory gene families of these three phytoseiid mites.The prey selection test showed that the early experience of feeding on western flower thrips can not affect the first prey selection of adult females of N.californicus – T.urticae strain and T.urticae was the preferred prey(93%).When the progeny of A.swirskii – C.lactis strain fed on T.urticae or F.occidentalis before emergence,the first prey selection of its female adults were significantly different from that of the offspring continued to eat C.lactis in early life history;When the progeny of A.swirskii– T.urticae strain fed on C.lactis or F.occidentalis before emergence,only the early experience of feeding on F.occidentalis significantly affected the prey selection of female adults at first.Regradless of the strain of A.swirskii,the early feeding experience increased the number of familiar preys selected by female adults.Based on the results of prey selection experiments in two predator mites,the prey selection of predators with a wider prey range was easily affected by previous feeding experience than predators with a relatively specialized prey range.This experiment explored the ultrastructure of potential chemosensilla at the tip of pedipalp and first pair of legs in P.persimilis,N.californicus and A.swirskii by scanning and transmission electron microscopy.There were 9 setae,which have the similar morphology and distributed pattern,at the tip of pedipalp across the three phytoseiid mites.In addition,there were 10 setae at the end of anterior legs in P.persimilis but 11 setae in N.californicus and A.swirskii.All three phytoseiids have two types of putative olfactory sensilla on the tip of the first pair of legs.The first type of olfactory sensilla contains many pores on their single wall and it was innervated by some dendrites in the inner fluid;the second type of olfactory sensilla has shallow groove on their second wall and the inner fluid with 1-2 dendrites was connected by the spoke channel.Of these,all three phytoseiid mites have 5 porous sensilla.However,the grooved sensilla in P.persimilis is 1 but N.californicus and A.swirskii have 2 grooved sensilla.The SEM and TEM graphs suggested that these predator mites have the potential chemosensilla at the tip of pedipalp and first pair of legs.Moreover,the difference in the number of chemosensilla may lead to the difference in the prey recognition among these phytoseiid mites.In this experiment,the types of chemosensory gene families and the number of their members were obtained by analyzing the transcriptome of precursors(including the pedipalp and first pair of legs)in these three phytoseiid mites.The results showed that there were no olfactory receptors(OR),odorant binding protein(OBP)and chemosensory protein(CSP)in all these species.However,the number of ionotropic receptors/ ionotropic glutamate receptors(IR/i Glu R)in P.persimilis,N.californicus and A.swirskii are 30,32 and 31.Similarly,the number of Niemann–Pick Type C2(NPC2)families are 16,14 and 19 in these three predator mites.These two chemosensory gene families may be involved in the transport and receptor of odors or chemical cues in phytoseiid mites.In conclusion,this thesis suggested the differences in prey selection behavior and chemosensory systems of these three predator mites,and provided the bases for chemosensory mechanism of prey recognition and field application in phytoseiid mites.