Adult fecundity, host plant preferences, field activity and parasitism in the leaf weevil Phyllobius pyri (L.) (Coleoptera: Curculionidae)

Abstract

AbstractAdults of the leaf weevil Phyllobius pyri (L.) (Coleoptera: Curculionidae) feed on a wide variety of broadleaved trees and occasionally cause severe defoliation in newly established farm woodlands. There is little information, however, on the relative susceptibility of different tree species to damage or on the habitat associations of adults and larvae of P. pyri, which might indicate the conditions that predispose trees to attack. Captures of adult P. pyri in emergence and flight traps in the current study indicated population densities in grassland of 0.5–6.4 adults per m2 at emergence but higher densities up to 13.5 per m2 in young pine plantations, where there was a mixture of grassy patches and young, naturally regenerating birch trees. The close proximity of larval food resources (grass roots) and a favoured adult host-plant, which also occurs in young farm woodlands, provided ideal conditions for P. pyri and allowed high population densities to develop. Feeding and performance experiments indicated that cherry, birch, oak and hornbeam were most susceptible to P. pyri, whereas field maple, hawthorn, rowan, lime and especially ash were resistant. Adult female P. pyri emerged in May reproductively immature and fed on tree foliage for 15.9±0.9 days before laying their first batch of eggs. Adults lived for 33.3±1.5 days, on average, and females laid a mean of 191.9±34.5 eggs (maximum=589) during their lifetime. Eggs hatched after 16–20 days. During 2003 and 2004, 11–16% of adult P. pyri were parasitised by Pygostylus falcatus (Hymenoptera: Braconidae) and 19–29% were parasitised by Rondania fasciata (Diptera: Tachinidae).