Population Dynamics And Interactions Among Phytoseiulus Persimilis,Neoseiulus Californicus And Tetranychus Urticae When Coexisting

For the past a few years,the importance of spider mites as greenhouse pests increases continuously.Biological control with predatory mites is one of the mainstream concepts in spider mite control.Phytoseiulus persimilis and Neoseiulus californicus ranked the top 2 mite predators of spider mites worldwide.Phytoseiulus persimilis was also the first predatory mite species introduced to China for biological control.Native N.californicus population was discovered in 2011 for the first time.In this study,the taxonomy status of native N.californicus population was verified through molecular markers.The population dynamics and distribution of P.persimilis and N.californicus when combined released for spider mite control were investigated under lab and field conditions.Main conclusions are listed as following:1.For all the 3 molecular markers(12S rRNA,cytochrome b mitochondrial DNA,and ITS),the Chinese population was in the same clade with all 15 other N.californicus populations from Europe,North and South America,Asia,and Africa,and they are all separated from the control species.The Chinese strain had the second shortest developmental duration when fed on Tetranychus urticae,and moderate fecundity and life table parameters compared to other populations.2.Lab experiments showed that P.persimilis population grows faster than N.californicus when the two species coexist with sufficient prey.When prey were provided after 48hr starving,the maximum population growth within 1 week decreased 45.0%and 26.6%for P.persimilis and N.californicus,respectively.The competition capability of P.persimilis decreased.Chances for N.californicus population growing faster than P.persimilis increased significantly.3.A 2-year field experiment on greenhouse cucumbers showed that combined release of the two predatory mite species are very efficient in reducing spider mite density.Density ratio of P.persimilis and N.californicus was able to be described using a power function against Tetranychus urticae density per plant.When T.urticae density was lower than 77.6 per plant,field density of P.persimilis was lower than N.californicus.When T.urticae density was higher than 77.6 per plant,field density of P.persimilis was higher.It is reasonable to expect the dominant predatory mite species exchanged around this critic spider mite density,which might also be the appropriate range for combined release of both predatory mite species.4.Both the two predatory mite species and T.urticae were aggregated distributed within each cucumber plant.The two predatory mites have similar aggregation levels,both being lower than that of T.urticae.For each species,its aggregation level was density dependent.The proportion of leaves with distribution can be described using Weibull distribution against density per leaf.For T.urticae,P.persimilis and N.californicus,50%leaves were occupied when densities were 9.7,2.8,2.6 per leaf,and 90%leaves were occupied when densities were 165.4,23.8,17.0 per leaf,respectively.Within increasing density,N.californicus became more dispersed than P.persimilis at within-plant level.Results of this study provides quantitative guides in determining spider mite sampling strategies and predatory mite release strategies on greenhouse cucumbers.It will be valuable to further establish a dynamic evaluation system with integrating results from the present study to biology of spider mites,predatory mites,and other interactions between multiple species and environmental factors.