[en] Blue Gum chalcid is a gall-forming wasp, which causes an extensive damage to Eucalyptus. It attacks mostly seedlings and field saplings. It causes damage on it's host by forming massive typical bump-shaped galls on trees canopy, specifically on the leaf midribs, petioles and stems of new growths. The pest was first reported in Kenya and Uganda in 2002 attacking the three major commercially grown Eucalyptus species; Eucalyptus grandis, E. camaldulennsis, E. saligna in East Africa. Eucalyptus is fast growing and widely planted in both plantations and farmers' woodlots. It is important for both industrial and domestic use. It is a major source of income generation for rural poor families. The objective of this study was to determine the spatial distribution, incidence and severity patterns of L. invasa and possible relationship to environment and biophysical factors in East Africa. Over 312 randomly selected stands were assessed for BGC incidence to it's distribution. In each identified stand 60 trees were selected from 3 randomly established plots of 20 trees each and BGC damage/incidence assessed on a 4-point scale. This was to determine the incidence and severity patterns. ANOVA using generalized linear procedures, regression analysis and correlation were done to determine the relationship between the percentage incidence of L. invasa infestation against altitude, age interval, agro-ecological zones and topography. There was widespread of pest in all the districts sampled. There was significant difference (p<0.05) on BGC incidence on agro-ecological zones. There was no significant difference (p>0.05) on L. invasa incidence among the three species. The study recommends that. further studies on damage and L. invasa population dynamics relationship to environment and biophysical factors should be conducted