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Euwallacea spp. (Coleoptera: Scolytidae) are polyphagous globally distributed invasive ambrosia beetles. One of the species was recently detected attacking Ricinus communis growing in Coffea canephora gardens in Uganda. This study was undertaken to: (a) determine the distribution, incidence, and relative abundance of Euwallacea sp. on R. communis in Uganda; (b) determine the influence of the presence of C. canephora on the incidence and abundance of Euwallacea sp. on R. communis; and (c) identify ambrosia fungus of Euwallacea sp. on R. communis. Five C. canephora farms with R. communis and five others with R. communis but without C. canephora were sampled in each of the six districts surveyed. Incidence of Euwallacea sp. on R. communis was measured, by inspecting the host trees in each farm for the presence or absence of the pest. Abundance of Euwallacea sp. on R. communis was estimated, by counting holes of Euwallacea sp. at the lower 1.7 m of R. communis stems. A fungus was isolated from galleries of Euwallacea sp. on R. communis and identified. Results show that Euwallacea sp. was present on R. communis in all districts surveyed, with 30–70% of the farms infested in each district and 5–28 holes of Euwallacea sp. found on each sampled stem of R. communis. Coffea canephora appeared to facilitate the infestation of R. communis by Euwallacea sp., although it did not seem to influence the multiplication of the insect inside the host. Cunninghamella echinulata appeared to be the ambrosia fungus associated with Euwallacea sp. Therefore, Euwallacea sp. is a threat to many economically important plants in Uganda that are known to be hosts of this pest. [ABSTRACT FROM AUTHOR]

Xylosandrus compactus (Eichhoff) is a serious pest of Coffea canephora and Theobroma cacao in Uganda and also attacks several common shade tree species often associated with these crops. Seedlings of 10 common hosts of X. compactus were screened for preferential infestation by X. compactus, with a view to analysing the potential role of the shade trees in escalating incidence and damage by the pest. The experiment was conducted for 8 weeks in a garden of mature C. canephora infested by X. compactus that served as a natural source of infestation for the seedlings. The seedlings that became infested by X. compactus were counted weekly and the counts subjected to generalized linear modelling. Results show marked host preference by X. compactus, with T. cacao and C. canephora being the most preferred, while Eucalyptus sp. and Albizia chinensis being the least preferred. Four simulated scenarios of incidence and damage by X. compactus on a preferred crop such as C. canephora are discussed. It is suggested that it is most unlikely for unpreferred alternate host shade tree species to markedly increase populations of X. compactus on shaded preferred host plants. However, these simulations, which are based on results from potted seedlings, need to be validated in a real field situation, taking into account other ecological parameters that are likely to influence pest populations. [ABSTRACT FROM AUTHOR]