Evaluation of blue gum chalcid infestation in eucalyptus woodlots in western Kenya

Abstract

Blue gum chalcid (BGC), Leptocybe invasa (Fisher & LaSalle), is a gall-forming wasp that belongs to the insect order Hymenoptera, family Eulophidae. It attacks a wide range of Eucalyptus species mostly between the seedling stage and five years of age. BGC causes damage to eucalypts by forming bump-shaped galls on the leaf midribs, petioles and stems. Severe infestation is manifested by twisted and knobbed leaves. The aim of this study was to establish the spatial distribution of BGC and extent of host plant damage in Eucalyptus woodlots in western Kenya. The study was carried out in six permanent sampling plots in Eucalyptus woodlots in Busia, Bungoma, Kakamega and Nyando. Trees were assessed for crown damage by estimating and classifying the density of galls on the leaves into four levels of infestation: low (less than 50% of the foliage canopy with galls and no twisted or knobbed leaves), moderate (greater than 50% of foliage with galls and less than 50% of leaves twisted and knobbed), high (greater than 50% of the leaves twisted and knobbed, galls on the twigs and some twigs deformed) and severe (greater than 50% of the twigs deformed and regeneration foliage observed). An evaluation of the pest’s infestation and extent of host plant damage indicated that, 4% of the trees had severe infestation; 5% high; 20% moderate and 70% low. Approximately 1% of the trees died as a result of loss of foliage attributable to severe infestation. Other observations from this study were that the severity of BGC infestation tended to decline as trees grew older and BGC infestation retarded tree growth.