Habitat Stability and Wing Length in Two Species of Arboreal Psocoptera

Abstract

Ectopsocus briggsi and Graphopsopus cruciatus are two common species of Psocoptera which feed upon the microflora growing on the leaves of trees in woods near Oxford. Specimens were collected over a five year period from three species of deciduous oaks and the evergreen oak, Quercus ilex, using mist spraying techniques. Data on seasonal distribution, abundance, sex-ratios and wing lengths are presented. The distribution of wing lengths show that the females of both species have a greater tendency towards brachyptery on the evergreen oak than on the deciduous oaks. None of the males are brachypterous. Both insect species are more common on the evergreen oak than the deciduous oaks. They both also overwinter on the evergreen oak but not on the deciduous oaks. Both species migrate from the leaf litter layer to the foliage of deciduous trees in the midsummer to exploit the short-lived abundance of food. It is concluded that the continuous availability of food on the evergreen oak has resulted in a reduction in the advantage of the migratory phase, which is evidenced by the shortening of the wings in the females.