Seasonal distribution and abundance of immature stages of the yellow-headed borer Dirphya nigricornis Olivier (Coleoptera, Cerambycidae) on coffee

Abstract

Seasonal occurrence of the beetle, Dirphya nigricornis Olivier, was monitored in the field for 3 years. Two coffee varieties, French mission and SL34 with capped and uncapped canopies respectively, were used to estimate the egg niches in two coffee estates at Ruiru, Kenya. The total egg niches in the short and long rainy seasons represented low infestation (1.56–8.21%), which was nearly stable throughout the study period, 1982–1984. In some cases, however, seasonal significant (P = 0.05) variety-to-variety differences existed between egg niches at each studied site. The distribution of the egg niches of D. nigricornis occurred on branches between the 1st and 21st internodes of primary and tertiary shoots of either variety. Egg niches were negatively correlated (r = -0.44 to r = -0.99, 19d.f.) to internode position in all five categories of the shoots examined. The beetle therefore concentrates infestation and does not place its progeny randomly on coffee shoots.