Interspecific Competition Between Herbivorous Insects In Hongyuan Alpine Meadow In The Northwestern Sichuan Province Of China

Interspecific competition not only drives species evolution but also affects population dynamics and community structure.Despite the fact that empirical evidence supporting interspecific competition is mostly derived from large vertebrates and invertebrates,it is still controversial whether interspecific competition is strong among herbivorous insects(except for insect outbreak).According to classic competition theory,competition for a limiting resource increases with niche overlap and population density.Theory(e.g.the green world hypothesis)also predicts that interspecific competition does not necessarily emerge between herbivorous insects because of complex life history and high predation rate(such that herbivorous insects are less likely to encounter each other).In particular,competition is hard to observe for parasitic herbivorous insects because they are small in small body size and live within host plant tissues and because infestation rate is usually low.In this study I experimentally determined interspecific competition between distantly related herbivorous insects and between closely related herbivorous insects in an alpine meadow of Hongyuan County,the northwest of Sichuan Province.The former experiment addressed the interspecific competition between two pre-dispersal seed predator species group including Tephritidae(laying eggs before flowering)and Gelechiidae(laying eggs after flowering)that infest Saussurea nigrescens.This experiment included four treatments:None(bagging),Tephritidae only(bagging after flowering),Gelechiidae only(bagging before flowering and open after flowering),Both(no bagging).The latter experiment addressed the interspecific competition among different species of Tephritid flies.Mature S.nigrescens capitula were collected(maturity indicated by the presence of withered flower tubes,when maggots had completed pupation)and the numbers and species of fly emergences were recorded.Moreover,young immature capitula were opened and the eggs,maggots and pupae were collected,and subsequently fly species were identified using DNA barcoding technology.Results of the experiment involving distantly related insects show that interspecific competition occurred between Tephritidae and Gelechiidae as indicated by the fact that the sum of the main effects of the two factors was greater than the effect of the mixture of two factors on the infestation rate,seed loss rate at capitulum level and at species level.Moreover,symmetric interspecific competition was found between Tephritidae and Gelechiidae,as each species group reduced the infest rate of the other species group.Results of the experiment involving closely related insects show that interspecific competition occurred among different species of Tephritid fly as the proportion of capitula in which different species coexisted(13%)was much greater before adult emergence than after adult emergence(0%).Moreover,the neutral hypothesis(assuming random encountering rate determines species coexistence probability)can effectively explain the different combination proportion of two fly species in a single capitulum.In summary,this study demonstrates a strong interspecific competition between distantly related and closely related herbivorous insects.Experimental testing may be an effective method to study the interspecific competition among herbivorous insects.