A genetic basis to the destruction of Eucalyptus globulus seed by wasps from the genus Megastigmus

Abstract

Megastigmus spp. are tiny wasps (bodies 2.5- 6.5mm in length) from the hymenopteran family Torymidae that destroy the seed of forest trees (Elliott and deLittle 1984). Many studies have examined their destructive effect on seed production in conifers, such as: Pseudotsuga; Abies; Cedrus; Cupressus; Juniperus; Larix and Picea (Roques and Skrzypczynska 2003). In Australia, they have been reported to feed on the seed of at least seven eucalypt species. However, despite reports of losses both in openpollinated seed orchard and controlled crossed seed of Eucalyptus globulus extending over many years, little is known of the biology and taxonomy of these insect species, nor the extent of the decrease in seed production they cause. The only study available suggests that the female wasps lay their eggs in eucalypt flowers (Drake 1974). After hatching, each small larva tunnel down into the developing seeds and gradually consume the content of a seed. The larva goes through several instars and the pupa develops within the seed coat. Fully-grown adult wasps emerge from the seed coat through a circular exit hole, and then exit through the top or side of the capsule usually before it opens. In this study we quantified the percentage of seed damaged by Megastigmus spp. predation in 384 seedlots of Eucalyptus globulus and examined whether there was a genetic basis to differences in the levels of seed predation observed.