Bernard Decazy

Frequency and distribution of Antestiopsis orbitalis Westwood (Hem., Pentatomidae) in coffee plantations in Burundi: implications for sampling techniques.

Abstract: The bug, Antestiopsis orbitalis Westwood (Hem., Pentatomidae), causes major damage in Burundi coffee plantations. Efficient management against this insect needs to have a reliable sampling procedure to estimate, with good precision, the level of the populations in coffee fields. Studies of the distribution and spatial dispersal of this bug are therefore required. To this purpose, an inventory of A. orbitalis in eight plots, of ≅ 100 coffee trees each, was undertaken. The number of bugs per tree fitted well to a negative binomial law, suggesting an aggregative behaviour of this insect. However, the aggregative coefficient was not constant on the different plots and adults were distributed in a more aggregative way than larvae. Study of the spatial dispersal of this bug generally indicated no particular structure (focus or gradient); only adults tended to be distributed according to gradients. Confidence intervals on the average number of bugs per tree were calculated following the robust method of bootstrap using different sized samples. Recommendations concerning sampling procedures are proposed.

Study of underground Adoretus versutus Har. (Col., Scarabaeidae) populations in Vanuatu: detection of cohabitation with other white grubs

In the absence of any natural enemies, Adoretus versutus has become the biggest threat to cocoa plantations in Vanuatu since its accidental introduction. Its biological cycle, from the egg stage to adult emergence, takes place in the top few centimetres of soil, preferably in pastures and near the host plants on which the adults feed. Various samples taken for a study of larva population dynamics revealed that five types of white grubs were likely to cohabit. Their existence and identification have to be taken into account before any attempt is made at biological control of A. versutus.