Constitutive chemical defense of Eucalyptus against herbivory by Gonipterus sp. n. 2

Abstract

The Gonipterus scutellatus species complex Gyllenhaal, 1833 (Curculionidae, Coleoptera) is comprised of 8 cryptic species native to East Australia and Tasmania. Of these 8 species only G. platensis, G. pulverulentus and Gonipterus sp. n. 2 are invasive pests. Gonipterus sp. n. 2 was first discovered outside of its native range in 1916 in South Africa, and caused widespread defoliation of Eucalyptus trees, preferentially feeding on young leaves and new shoots. In 1926 Anaphes nitens Girault, 1928 (Hymenoptera: Mymaridae), an egg parasitoid, was discovered and released in South Africa. Anaphes nitens was historically very effective until the early 2000’s when large outbreaks of the beetle were occurring with increasing frequency. Therefore, investigations for alternative management options were initiated. Both biopesticides and pesticides were tested. However, biopesticides showed little reduction in beetle populations and pesticides are expensive and under legislative control, thus lowering accessibility and hampering large scale use, which results in inefficient control of the beetle. However, Gonipterus sp. n. 2 shows a very distinct host selection behavior, preferentially feeding on certain Eucalyptus species and not at all on others. Several studies have indicated Eucalyptus defense compounds, (such as 1,8-cineole) which may be able to repel Gonipterus sp. n. 2 and could partially explain this selective feeding behavior. Therefore, understanding these compounds which potentially mediate the feeding behavior of Gonipterus sp. n. 2 can offer an alternative control strategy for these beetles. However, this feeding preference has not been studied in depth and more research is needed to understand how these compounds can be developed into a control measure for commercial Eucalyptus plantations. Therefore, the inherent resistance mechanisms of the plant against feeding by Gonipterus sp. n. 2 should further investigated.