Development of larvae of the whitefringed weevil,Graphognathus leucoloma(Coleoptera: Curculionidae), in northern Queensland

Abstract

AbstractGrowth of larvae of the whitefringed weevil,Graphognathus leucoloma(Boheman), was studied in the laboratory and on various crops in pots in a shadehouse at Kairi, on the Atherton Tableland in north Queensland. In the laboratory at 25.5 ± 1°C there were 11 instars for which head capsule widths and weights were recorded. The first instar weighed 0.14 mg. This was a non-feeding stage capable of prolonged survival, and after 10 weeks in soil without food 60% survived. When provided with carrot (Daucus carota) larvae grew to 2 or 3 mg after 6 to 7 weeks, then increased rapidly in weight reaching 140 mg after 120 days. At 25.5°C the average time from first instar to adult was 311 days, due in part to a long prepupal period. Larval growth was measured on the roots of peanut (Arachis hypogaea) plants in pots in summer and winter. Under summer conditions (mean soil temperature 23.3°C) larvae reached 140 mg in about 120 days, similar to that in the laboratory on carrot. These fully grown larvae remained in the pots over the mild winter without pupating. Larvae developing in autumn/winter grew more slowly, but the fully grown larvae were then exposed to high spring (early summer) temperatures and soon pupated, the average time from first instar to adult being 273 days. The indications are that temperatures above 25°C quickly precondition mature larvae from Tolga for pupation, thus explaining the broad timing of adult emergence in the field in north Queensland. On different plants common near Tolga, larvae grew most quickly on peanuts and on the pasture legumes dolichos (Lablab purpureus) and stylosanthes (Stylosanthes guianensis). Survival on maize equalled that on peanuts (46.5% in sterilized soil) but growth was less. Larval survival and growth on the grass crowsfoot (Eleusine indica), and (surprisingly) on the pasture legume glycine (Neonotonia wightii) was very poor.