PhD thesis. Abomey-Calavi University, Benin

Abstract

Weaver ants live exclusively in trees and shrubs, where they build nests with fresh plant leaves. Oecophylla ants are used commercially to control insect pests and for protein production.

In this thesis, we identified the period of occurrence of sexuals in O. longinoda (Latreille) colonies in Tchaourou, in Borgou department, a region characterized by unimodal rainfall pattern. We also investigated methods to trap mated queens that can subsequently be used to stock ant nurseries. Our observations indicate that sexual forms of weaver ants were observed in the colony from January to the beginning of August depending on the year, with abundance peaks from March to June. Weaver ant winged queen and male productive period began during the dry season and mating flights appeared to be triggered by rainfall, suggesting that populations in areas with long rainy periods may show prolonged mating periods compared to populations in extended dry season areas. Several mating flights were observed over a rainy season in unimodal rainfall. We also determined that leaf trapping was the most efficient method to collect queens followed by paper traps and search & catch. These methods can provide fertilized queens of weaver ants in sufficient numbers and therefore show to be appropriate methods for artificial colony production. This can also make weaver ant management easier and more successful to farmers which again may improve the chances of a wide implementation.

To improve the technology of artificial colony production and implement it on a large scale, effective and fast production of live colonies, we tested if multiple queens and transplantation of pupae could boost growth in young O. longinoda colonies. Colonies with two queens artificially placed in the same nest, all perished due to queen fighting, suggesting that pleometrosis is not used by O. longinoda. Within the 50-day experiment, the total number of individuals in colonies with 50 and 100 pupae transplanted, increased with 169 and 387 %, respectively, as compared to colonies receiving no pupae. However, we observed that queens were unable to handle 300 pupae adequately and that pupae require some amount of nursing as grooming, protection and temperature/humidity control by carrying pupae to optimal micro climates. Nevertheless, within the 60-day experiment, the transplantation of 300 pupae increased total colony size more than 10-fold whereas 100 pupae increased the size 5.6 fold, compared to control. The size of hatching pupae produced by the resident queen also increased with increase of the number of pupae transplanted.

We tested how sugar feeding impacts newly mated O. longinoda queens during both claustral founding and after claustral stages. We observed that the intrinsic brood produced by resident queens did not directly increase colony size in the colonies that received sugar and control during claustral founding. A newly-mated weaver ant queen, O. longinoda, uses her stored body reserves to rear the first generation of nanitic workers.

The research approaches developed in this thesis has allowed to identify the mating season and flight in the unimodal rainfall and to develop methods to trap high numbers of newly fertilized (mated) queens that can also be used to produce weaver ant colonies in ant nurseries. It also shows that pupae transplantation may be used to shorten the time it takes to produce weaver ant colonies in ant nurseries, and may, in this way facilitate the implementation of weaver ant biocontrol in West Africa.