Behavioral Response Of Green Lacewing,Chrysopa Pallens(Rambur)to The Trap Plant Alfalfa And Biological Control Of Western Flower Thrips,Frankliniella Occidentalis(Pergande)

Western flower thrips,Frankliniella occidentalis(Pergande)(Thysanoptera: Thripidae)is an important invasive polyphagous pest in vegetable and ornamental crops worldwide.The increasing resistance to chemical insecticides in F.occidentalis has resulted in heightened interest in alternative control methods including the generalist entomophagous predator Chrysopa pallens(Rambur)(Neuroptera: Chrysopidae).The green lacewing,C.pallens can prey a wide range of insect pests that have caused economic damage on vegetables and ornamental plants in China.This thesis investigated about the predation capacity of C.pallens to F.occidentalis in both laboratory and glasshouse conditions.Suitability of F.occidentalis as a prey for C.pallens was also investigated compared with its common prey Acyrthosiphon pisum(Harris)(Homoptera: Aphididae).Finally,the potentiality of alfalfa,Medicago sativa L.(Fabaceae)has been evaluated as a trap crop to the attraction of the green lacewing,C.pallens.(1)To evaluate the prey capacity of the C.pallens larval instars on F.occidentalis larvae,functional responses experiment has been conducted.The C.pallens larvae exhibited a Holling type III functional response to the F.occidentalis larvae.When offered 80 thrips larvae,34-41 were consumed by a single C.pallens larvae within 24 h.Later on,in glasshouse cultivated cucumber,the effect of releasing C.pallens to control F.occidentalis has been examined.In comparison with the control,releases of C.pallens larvae at densities of 2,4,8 and 16 per plant led to a reduction in F.occidentalis by 11%,39%,59%,68% of the larvae and 12%,43%,58%,68% of the adults respectively in 2017 and 35%,52%,57%,67% of the larvae and 30%,48%,60%,69% of the adults respectively in 2018,after five weeks.Our results indicated the C.pallens may be an effective biological control agent for use against F.occidentalis.(2)The developmental durations of C.pallens larvae were significantly different among larvae fed the two different preys(A.pisum and F.occidentalis).The developmental duration from first instar to adult emergence was shorter when larvae were fed A.pisum(22.56 ± 0.39 d)than on F.occidentalis(29 ± 0.45 d).Survival rates of C.pallens from first instar to adult emergence were 22.6% higher when they fed A.pisum than fed on F.occidentalis.The possible implications of these findings for mass-rearing of C.pallens and for understanding its biology and survival capacity in agro-ecosystem in relation to the availability of different prey species.(3)From behavior response experiments,it has been observed that,C.pallens adults exhibited attraction to volatiles from both flowering and non-flowering alfalfa;however,there is no difference in C.pallens attraction on odors release from thrips infested alfalfa and artificial food spray in Y-tube olfactometer studies.Furthermore,the volatiles emitted from flowering and non-flowering alfalfa which can attract C.pallens.Headspace analysis revealed that,only flowering alfalfa emits methyl salicylate and(E)-β-Farnesene and(E)-β-ocimene emits from both flowering and non-flowering alfalfa plants.Thus,individual or mixtures of these alfalfa volatiles may be useful to attract green lacewing for a successful biological control strategy.