Studies on the biology of the gorse seed weevil, Exapion ulicis (Forster 1771), in Northern California (Coleoptera: Curculionidae)

The seed weevil, Exapion ulicis (Forster 1771), was released in northern California as a biological control agent against gorse, an exotic shrub that invades grasslands and wildlands in the coastal counties of California. Several studies were conducted to examine the relationship between egg maturation and deposition with the flowering phenology of its host plant. Female weevils fed different diets of flowers and foliage showed significant differences in ovarian development. Females relied on their stored fat reserves to sustain them through the winter season. Stored fat in newly emerged females was 21% in June or July, declining to 10% by late January the following year. Fat maintenance was sustained throughout the ovipositional period by both flower and foliage feeding. The results show that the biology and life cycle of this weevil was closely tied to the production of flowers by gorse. Oviposition was synchronized with anthesis and flower feeding in March (early spring). Larval development occurred in late March through mid-May and adult emergence began in early M ay. Larval consumption of seeds was the primary means of feeding damage. When present, larval feeding reduced seed number per pod between 64% and 87%. Infestation of seedpods by weevils varied from 4% (late March) to 71% (early June) and translated to a population-level estimate of seed destruction of 51%.