Effects Of Tomato Spotted Wilt Virus On The Mating And Feeding Behaviors Of Its Vector Western Flower Thrips

The western flower thrips(WFT),Frankliniella occidentalis is a major pest of horticultural crops around the world.It damages crops by feeding in rasping sucking manner on different parts of the plant.F.occidentalis can also transmit Tomato spotted wilt virus(TSWV)in a persistent-propagative manner during probing.Mutual benefit exists between TSWV and F.occidentalis.TSWV infection can increase the feeding,survival rate and fecundity of the thrips and then promote the spread of virus.We assume that some reproduction-related activities such as mating behavior and pheromone may change in its vector due to the infection of TSWV.In the present study,the effect of TSWV infection on mating behavior(initial copulation,copulation duration,post copulation,female re-mating frequency and male harassment rate),pheromone production and pheromone detection,and feeding behavior were investigated.The results of the research will increase our understanding on the interaction between TSWV and F.occidentalis and then make suitable management strategies to them.In the mating behavior experiment,four cross treatments were designed that were consisted of paired TSWV infected and uninfected male and female thrips.The average pre-copulation period was observed 86.795±10.837s(range from 53.75 t o 121.65 seconds).TSWV infection significantly increased the copulation duration,but the initial copulation duration between viruliferous and non-viruliferous thrips was not affected.The average copulation duration ranged from 82.15 to 249.5 seconds.Virus infection decreased the female re-mating frequency significantly in viruliferous thrips.Throughout the entire remating periods 60 % of non-viruliferous females re-mated with non-viruliferous males while 35% of viruliferous females re-mated with viruliferous males,and 25-30 % of females re-mated with males in the absence of TSWV infection in one of their partner.Moreover,male harassment was significantly higher in virus infected males of WFT.In equal ratio of male and female cross paired experiments,the number of males' progeny was observed higher than the females'.Thus,the offspring sex ratio were changed from female-biased to split or even male-biased in the TSWV-infected thrips.In the pheromone experiment,the effect of TSWV on the aggregation pheromones contents,and response of F.occidentalis females towards male odors were examined by using Y olfactometer and GSMC respectively.The results showed that TSWV infected females were observed less attractive towards the male odors than the control odors.The preference of adult females of non-viruliferous of susceptible thrips towards were 70% but viruliferous were 60%,which is lower than healthy thrips.Similarly,NIL-R adult females were attracted to the odours of adult males of 63% of non-viruliferous status then the 54% for viruliferous.No significant difference was observed in the pheromone titer between spinosad-susceptible and-resistant thrips with and without TSWV infection.Two new pheromones compounds n-hexadecane and n-heneicosane were discovered.The n-heneicosane compound was found higher in virus infected males in both susceptible and resistant lines.In the feeding behavior experiment,initially we determined the effects of acquisition access period(AAP)on virus titer,virus acquisition capacity and the transmission rate on pepper plant.There was no significant effect of AAPs on TSWV titer at the nymphal stage in susceptible and resistant thrips except 24 h AAP.Whereas,the low virus titer was detected in F.occidentalis adults at the 6 h AAP in both strains.The percentage of thrips with TSWV was found significantly higher in adult at 96 h AAP in any strain.But spinosad resistant F.occidentalis transmitted the TSWV significantly efficient at 96 h AAP than the susceptible thrips.Therefore,the feeding behavior were studied at 96 h AAP,because it possessed higher virus transmission rate.Infected males made a significantly greater number of non-ingestion probes on healthy pepper in both strains,which means virus transmission may increase.Whereas,non-viruliferous males fed more in term of long-ingestion probes than the infected males on healthy pepper in susceptible thrips,thus increasing the food uptake.Our results not only widen our knowledge on insect-virus interactions but also strength assistance in the progress of strong ways to integrate the management of TSWV and F.occidentalis in agroecosystems.We can conclude that virus modifies the mating,feeding behavior,aggregation pheromones contents of its vector to promote virus transmission.In future,researchers may develop new technique to suppress this mutual interaction in an integrated pest management program.