The Biological Control AgentAcanthoscelides macrophthalmus(Chrysomelidae: Bruchinae) Inflicts Moderate Levels of Seed Damage on Its Target, the Invasive TreeLeucaena leucocephala(Fabaceae), in the KwaZulu-Natal Coastal Region of South Africa

Abstract

Leucaena leucocephala (Lam.) de Wit (Fabaceae), an agroforestry tree with invasive properties, was targeted for biological control in South Africa. The seed beetle Acanthoscelides macrophthalmus (Schaeffer) (Chrysomelidae: Bruchinae) was released in 1999 to curb its excessive seed production without negating its beneficial properties. The adult beetles oviposit on the seed pods and loose seeds of L. leucocephala and the hatching larvae enter the seeds and destroy them during their development. Although the beetle has become widely established in South Africa, its contribution to the weed's management is unknown. The aims of this pilot study were to assess: (i) the levels of seed damage inflicted by A. macrophthalmus on L. leucocephala populations and; (ii) the extent to which the endophagous immature stages have recruited native parasitoids. The study was carried out over seven months at three sites in the KwaZulu-Natal coastal region, where L. leucocephala is abundant. Mean seed damage was inconsistent, with considerable variation (2–62 %) between sites and time of collection. On average, <30 % of available seeds was damaged at each site. Five species of parasitoids (Hymenoptera: Chalcidoidea) were consistently reared from beetle-damaged seeds, two of which (both Pteromalidae) were most commonly associated with the beetles. Mean mortality resulting from parasitism was similarly inconsistent and variable (1–22 %) between sites and time of collection. Although parasitism increased with increased seed damage, on average only 7–9 % of larvae/pupae were parasitized at the three sites. The modest levels of seed damage recorded in this study appear insufficient to regulate populations of L. leucocephala in South Africa.