Intraguild Predation Involved By Neoseiulus Barkeri And Control Effects In Greenhouse

The predatory mite, Neoseiulus barkeri is a generalists mainly preying on spider mites and thrips and get widely used in the current biological control in China. In this thesis, we studied cannibalism and intraguild predation between the phytoseiid mites N. barkeri and and Neoseiulus cucumeris, and further evaluated female aggressiveness (quantified as attack probability) in intraguild predation on larvae, and then investigated the effects of cues of an intraguild predators (IG-predator) on the distribution of its intraguild prey (IG-prey) in order to elucidate the interaction in these two species of predatory mite for reasonable combination of different natural enemies in biological control. Meanwhile, the control effects of N. barkeri on spider mites on cucumber and bean plants in greenhouse were evaluated, respectively. The main results were as follows:1. The two species of phytoseiid mites N. barkeri and and N, cucumeris consumed more con-and heterospecific larvae than protonymphs, and seldom consumed con-and heterospecific eggs. Adult females of both predators exhibited higher predation rates on heterospecific larvae and protonymphs than on conspecific larvae and protonymphs, suggesting that two species of phytoseiid mites preferentially engaged in intraguild predation in absence of other food sources. The predation rate of N. barkeri with heterospecific larvae and protonymphs was higher than the predation rate of N. cucumeri with heterospecific larvae and protonymphs; moreover, N. barkeri was more aggressive against heterospecific larvae than N. cucumeri in intraguild predation. Hence, N. barkeri was most probably a potential intraguild predator (IG-predator) of N. cucumeris and whereas N. cucumeri was a potential intraguild prey (IG-prey) when intraguild predation occurred between N. barkeri and N. cucumeris.2. The effects of cues of an IG-predator, the predatory mite N. barkeri, on the distribution of its IG-prey, the predator mite N. cucumeri, were studied in this chapter. The results showed that the proportion of IG-prey on patches with cues of IG-predators was significant lower than on patches without cues of IG-predators, suggesting that IG-preys can rapidly assess predation risk based on the cues from IG-predators and chosen the more secure patches. IG-prey also avoided patches where conspecific juveniles had been killed by IG-predators. The IG-prey laid fewer or no eggs on patches with cues of IG-predators. the majority of eggs laid by the IG-prey on patches without cues of IG-predators. Hence, IG-prey showed antipredation behaviour to its IG-predator by changing their distribution and oviposition in response to cues of IG-predators. This possibly further explained why intraguild predation is common in nature.3. To evaluate the ability of N. barkeri against spider mites, two series of preventive experiments on cucumber and bean plants in greenhouse were conducted in spring and on autumn in2012, respectively. The population of spider mites on plants with predators was consistently lower than on plants without predators, where the population of spider mites grew exponentially. Releasing N. barkeri could achieve longer and more stable effects than using acaricides in suppressing the population of spider mites although it needed a longer time than acaricides. Concersely, the population of spider mites on plants with acaricides resurgenced again shortly after no chemicals used anymore. These results proved the sustainable effects of N. barkeri on suppressing the population of spider mites as a biological control agent.