The weaver ant, Oecophylla smaragdina (Hymenoptera: Formicidae), an effective biological control agent of the red-banded thrips, Selenothrips rubrocinctus (Thysanoptera: Thripidae) in mango crops in the Northern Territory of Australia

Abstract

Weaver ants, Oecophylla smaragdina (Fabricius), have been successfully used to control the main insect pests of cashew plantations in northern Australia and Papua New Guinea. The red-banded thrips, Selenothrips rubrocinctus (Giard), is an economically important insect pest of mango, Mangifera indica L., orchards in the Northern Territory. This work was undertaken to evaluate whether weaver ants, which are abundant in mango orchards, have the potential to control the red-banded thrips. Field surveys, field experiments and laboratory trials were carried out in four mango orchards in the Darwin area over four years. In field surveys, the number of shoots damaged by the thrips was significantly lower on trees with abundant weaver ants (2.8%) than with fewer ants (21.1%), or without the ants (30.3%). Trees with abundant weaver ants also produced the highest numbers of flower panicles. Leaf examinations revealed that newly mature leaves on trees with abundant weaver ants had significantly fewer thrips than on trees with fewer or no ants. Field experiments showed that weaver ants were as effective as chemical insecticides in limiting fruit damage by thrips. In laboratory trials, seedlings without weaver ants were heavily damaged, and lost all their leaves within six weeks, while seedlings with weaver ants grew well and lost no leaves. This work suggests that the weaver ant is an effective biological control agent of the red-banded thrips, and the use of weaver ants in mango orchards is discussed.