Predation And Non-consumptive Effect Of Amblyseius Swirskii On Co-existence Between Frankliniella Occidentalis And Bemisia Tabaci

The interspecific competition of pests will directly or indirectly affect the population quantity and community structure of pests,and then affect the occurrence and harm of dominant pests in agricultural ecosystem.Broad-spectrum natural enemies often mediate the interspecific relationship of prey through consumptive and non-consumptive effects when controlling multiple co-existence pests with overlapping ecological niches in the same crop system,thus affecting their comprehensive control effect against co-existence pests.Since the invasion of the world’s major invasive pests,western flower thrips Frankliniella occidentalis and the sweetpotato whitefly Bemisia tabaci,occur frequently at the same time in plant vegetable system,which results in huge economic loss for the planting production of vegetable in greenhouse.Amblyseius swirskii is a commercially produced and highly efficient predatory mite,which is widely used to control small succulent pests such as whitefly and thrips in greenhouse systems.In order to determine the effect of A.swirskii on the interspecific relationship between F.occidentalis and B.tabaci during their mixing,we measured the differences of consumptive predation and preference of A.swirskii on the two pests at the laboratory level,and studied the non-consumptive effects of predatory mite intervention on feeding behavior,growth and reproduction of co-existence pests.The effects of A.swirskii on the population dynamics of two pests in cucumber plants were monitored under greenhouse conditions.The main results were as follows:1 Consumptive predation and preference of A.swirskii against F.occidentalis and B.tabaciAmblyseius swirskii began to prey on pests and mites after it entered protonymph stage.By measuring the total predation and daily predation of the first instar nymphs of F.occidentalis and the eggs and first instar nymphs of B.tabaci in the cumulative predation period of A.swirskii,it was found that A.swirskii developed from the first instar nymphs to adult mite until death.The total and daily predation of first instar nymphs of B.tabaci were significantly higher than those of eggs of B.tabaci and first instar nymphs of F.occidentalis.The predation selectivity of adults male and female of A.swirskii and deutonmph to F.occidentalis and B.tabaci under different density combinations was measured.It was found that the predation preferenc of adult female mites of A.swirskii was affected by density and preferred to prey on the prey with high density when the prey combination was the first instar nymph of F.occidentalis and the first instar nymph of B.tabaci.Deutonmph and adult male mite were not affected by the density,they preferred to prey on the first instar nymphs of B.tabaci.When the prey combination was the first instar nymph of F.occidentalis and the eggs of B.tabaci,the adult female and male of A.swirskii were not affected by density,and the adult female mites selectively preys on the first instar nymph of F.occidentalis.Adult male and deutonmph mites selectively prey on the eggs of B.tabaci.2 Non-consumptive effects of A.swirskii on F.occidentalis and B.tabaci under predation risk stressThe non-consumptive effect of A.swirskii on target prey is mainly that it does not contact the prey directly and induces the prey to have defensive response through its presence signal.The frequency of contact with natural enemies,defensive behavior,time and area of feeding on host plants were measured under predation risk stress of A.swirskii.The results showed that under the predation risk stress of A.swirskii,the proportion of feeding time of F.occidentalis and feeding area was reduced significantly,and the frequency of encounters and defensive responses increased significantly.By comparing the growth and development of F.occidentalis and B.tabaci under the interspecific interaction,it was found that the developmental period of F.occidentalis was shortened and that of B.tabaci was prolonged under the interspecific interaction.On this basis,the predation risk stress of A.swirskii was introduced.The results showed that under predation risk stress,the development period of F.occidentalis was not affected,while B.tabaci significantly shortened the development time of the most vulnerable stage of predation and reduced the risk of predation.At the same time,the oviposition of F.occidentalis and B.tabaci under predation stress was measured.It was found that the single female oviposition of F.occidentalis and B.tabaci decreased by 17% and 20%,respectively,compared with the control group,but the total oviposition of B.tabaci was significantly higher than that of F.occidentalis.These results indicate that although thrips are in a dominant position when their development is accelerated in the interspecific competition,B.tabaci has the potential to develop into a dominant species under the non-consumtive action of A.swirskii.3 Population dynamics of F.occidentalis and B.tabaci after the release of A.swirskiiPopulation dynamics of single prey species,F.occidentalis co-existence with B.tabaci,and A.swirskii coexisting with F.occidentalis and B.tabaci were investigated under greenhouse conditions.The results showed that the population of B.tabaci increased on cucumber plants affected by single prey,while the population of F.occidentalis vstabilized from the 5th week after release.The population of B.tabaci in cucumber plants co-existence with the two species showed an increasing trend,while the population of F.occidentalis showed a decreasing trend from 4 weeks after release,indicating that B.tabaci was the dominant species.Population dynamics of B.tabaci and F.occidentalis were still increased and that of F.occidentalis decreased under the mediated action of A.swirskii.Population of F.occidentalis was significantly lower than that without predatory mites for many times,and the population of B.tabaci was significantly lower than that without predatory mites only at the 8th week.These results indicate that the intervention of A.swirskii does not change the status of B.tabaci as the dominant species in co-existence with F.occidentalis.In conclusion,this study studied the direct feeding,non-consumtive action and population dynamics of the natural enemy A.swirskii on F.occidentalis and B.tabaci and determined that B.tabaci was always the dominant species when A.swirskii entered the cucumber plants that were damaged by them.A.swirskii can better control the occurrence of F.occidentalis when the mixture occurs,but other measures should be taken to clearly control the further occurrence of B.tabaci.The results of this study provide a theoretical basis for formulating more accurate,targeted and specific integrated pest management measures,and provide technical support for improving the damage control effect of natural predators on predatory mites.