The Asian longhorned beetle Anoplophora glabripennis is a wood-boring beetle that,upon severe outbreaks,causes great damage in the artificial shelter-forest of the Three-Northern Areas.The great spotted woodpecker Picoides major is one of the natural predators of A.glabripennis.P.major is also a common species in Wulate Qianqi of the Inner Mongolia Autonomous Region and is widely distributed in the artificial shelter-forest.The wood-boring beetle is an important food source of P.major,especially during the winter.Despite the potential of P.major to control A.glabripennis populations,surprisingly little is known about their predator-prey interactions.This information is essential to predicting the efficacy of P.major as a control agent to A.glabripennis.Therefore,it is important to study how the predator responds to changes in prey density.From 2006 to 2008,fifteen study plots were selected,and the predation of P.major on A.glabripennis was examined with sample plot and trace investigation,the latter being in the field.The results showed that the function response of P.major to A.glabripennis was Holling Ⅲ,with a non-linear regression equation.The increase in predation capacity correlated with the increase in A.glabripennis density,within a certain density range.As the density of A.glabripennis increased,the predatory capability had a positive acceleration phase,then a negative acceleration phase,and finally a saturation state.Likewise,as the density of A.glabripennis increased,the predation rate initially increased,peaked,and was reduced in the end,with a non-linear regression equation.The results indicated that the numerical response was a positive reaction to density.In other words,the population density of P.major increased as the density of A.glabripennis increased.
As one of the natural predators of Asian longhorned beetles Anoplophora glabripennis(Motsch.)(Coleoptera:Cerambycidae),the great spotted woodpecker Picoides major(Linnaeus) is endemic to Wulate Qianqi County and is widely distributed in the artificial shelter-forest of the Inner Mongolian Autonomous Region.From December 2006 to January 2007,the rate of predation on A.glabripennis by P.major was investigated in Wulate Qianqi County in 27 field plots,where P.major and A.glabripennis coexist and in which trees were damaged by A.glabripennis.In addition to the field studies,24 host trees of A.glabripennis were cut down for further examination.Data on the quantities of A.glabripennis,including beetles which were pecked by P.major,were collected from each field plot and every cut-down tree.The data showed that the pecking rate of P.major foraging for A.glabripennis was 14.91% in low damaged plots,19.86% in medium damaged plots and 13.93% in the high damaged plots,respectively.The rate of pecked A.glabripennis found above 6 meters was 27.25%.That was noticeably higher than the rate of pecked A.glabripennis found under 6 meters on the trees,(16.18%).Results also showed that P.major preferred old A.glabripennis larvae over young larvae in both the damaged plots and at greater heights.These results suggest that P.major foraged for A.glabripennis selectively:i) exhibiting a high selectivity in the medium damaged plots;ii) preferentially selecting the appropriate damaged heights;iii) preferentially selecting older larvae,while occasionally selecting a few young larvae.Finally,the reasons of foraging selectivity are discussed in relation to economic factors and methods;such as cost-benefit analysis,trade-off of foraging and risk,and predation risk analysis,based on optimal foraging theory.
