ECOLOGY AND MANAGEMENT OF BITING ANT, Tetramorium aculeatum MAYR (HYMENOPTERA: FORMICIDAE) IN COFFEE, Coffea arabica L. IN SOUTHWESTERN ETHIOPIA

Abstract

Biting ant, Tetramorium aculeatum Mayr (Hymenoptera: Formicidae) is an important pest in coffee that affects farming activities in Southwestern Ethiopia. The objectives of this study were to assess farmers’ knowledge and pest management practices of biting ant understand the ecology of biting ant in Southwestern Ethiopia, and evaluate the efficacy and potential of some insecticides. Survey was conducted on 180 coffee farmers in 12 districts. Spatial distribution of biting ant was studied in eight coffee farms and analyzed by semivariance using geostatistics (GS+10). Nine insecticides treatments were evaluated both under ex-situ and in-situ conditions in CRD and RCBD designs, analyzed by analysis of variance. Most of the farmers interviewed (58.9%) recognize the problems of biting ant in coffee and some (23.3%) of them are knew this ant for about ten years. Significant variations were observed in the levels of infestation and abundance of the biting ant in different ecology of coffee producing districts and production systems. Lower altitudes and private coffee plantations had higher number of nests. The biting ants within coffee plant are aggregate on the tree. The semivariogram of the biting ant characterized with localized discontinuity and long range correlation in some coffee farms and vice versa in the others indicating spatial dependence of biting ant nests between samples pairs. The spatial distribution trends of the nest in the field showed aggregated along the center and in some farms near corners and declined from there across to the inner field. Under the ex situ evaluation, all the insecticide treatments caused significantly (p≤0.01) higher mortality (100%) of biting ants and caused complete mortality within 24 hours. Under field condition the insecticides showed significant variations on percent of evacuated nests. However, the two botanical insecticides, oxymatrine and nimbicidine, performed significantly (p≤0.01) as par with the other tested insecticides up to 18th day after application. On the other hand, deltamethrin 2.5% at the rate of 0.75ml/l of water caused significantly highest percent of evacuated nests and less number of newly constructed nests of biting ant (0.2) after thirty days of application. Generally deltametrin 2.5% at 0.75ml/l can be used for heavily infested farms where pruning and manually destructing the nest difficult and the future it is important to conduct insecticide evaluation with additional botanical based insecticides, and also undertake residual effect analysis of deltamethrin insecticide in coffee environment.