Performance of first instarChrysophtharta bimaculata larvae (Coleoptera: Chrysomelidae) on nine families ofEucalyptus regnans (Myrtaceae)

Abstract

In bagged and unbagged shoot experiments, we investigated the survival and growth rate of first instar larvae ofChrysophtharta bimaculata on 9 families of a natural host,Eucalyptus regnans. Families used had been previously assessed as being either of low or high susceptibility toC. bimaculata damage. In conjunction with larval experiments, we measured 24 tree and leaf characteristics (including foliar elemental concentrations, foliar terpenes, leaf toughness and tree growth rates) and attempted to correlate the plant characters measured with differences in larval performance and previous scorings ofE. regnans family susceptibility. First instar larval growth and survival did not differ significantly across families or between low and high susceptibility family groups (=susceptibility classes), although survival was significantly greater in bagged than unbagged treatments. As predators were in low abundance at the study site, we attribute higher survival rates of larvae in bagged treatments to increased protection from adverse weather conditions. Only one plant character measured, an unidentified foliar phlorglucinol, was significantly negatively correlated with larval survival. Of the 24 plant characters measured, 11 were significantly different between families and 10 were signficantly different between susceptibility classes. Only 4 plant characters were significantly different at both the family and susceptibility class levels;viz. proportion red leaves, tree height at end of season, trunk volume at end of season and relative growth rate based on tree height. Principle Component Analysis using all plant characters measured, or subsets of them, could not separate individual families or susceptibility classes. Our results suggest that herbivore resistance mechanisms inE. regnans do not affectC. bimaculata larvae, but may influence adult feeding and/or oviposition.