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.

Résumé

La periode du searabeé D.N.O. etact, suivie air le terrain pendant 3 ans. 2 varieties de café, Mission francaise (French Mission) et SL34, avec respectivement desherboge et non desherbage du couvert vegetal, ont èti’utilise’es pour l’estimation ds, nids dans un domain de café a Ruiru, Kenya. De nombre total traduisait une faible infestation (1,56%–8,21%) pour une courte ou une longue saison de pluies, pendant d’etude 1982–84. Cependant, certains cas avaient ds differences saisonnie’rs importantes selon is varietie’s et selon es sites d’étude. Les nids se distribunient entre es le et le 21^e internodule aes fenns pousses, primaires et tertiairs, de chaque variet’s. Cette correlation n’eoistait pas chez 5 jeune pousses esaminus. Par consequent, le searab’ee concentre is infestations et ne place pas sa progeniture an hazard.