Adaptation of Helopeltis schoutedeni Reuter (Heteroptera: Miridae) to planted Eucalyptus in the Congo: damage and control.

摘要

Eucalyptus is grown at low latitudes in all continents. In these allochthonous plantations, a discrete and little diversified entomofouna is known, mostly composed of phytophagous insects, specific to Eucalyptus in their native areas. The area of Pointe-Noire in the Congo, however, is an exception, proving that the situation is evolving. A mirid of the genus Helopeltis, H. schoutedeni, develops in large numbers in the youngest plants (less than 3 yr old). Levels of infestation are not influenced byforest edges. H. schoutedeni seems to be found on rapidly-growing turgescent plant tissue, and has already proved its capacity to extend its trophic niche towards other new plants (cotton, cocoa). However, concerning the degree of success of H. schoutedeni, great differences in infestation can be observed between Eucalyptus spp. and even between clones. A comparison of clone susceptibility has demonstrated the close link between feeding activity and the number of eggs laid in plant tissue. The maximumnumber of these mirids per 1-yr-old plant exceeded 20 nymphs in March and 7 adults in April. Then, both seasonal drought (from June) and the aging of the young plant combine to limit populations. On 2-yr-old plants, the numbers of H. schoutedeni decreased by half. The capacity of Helopeltis to attack Eucalyptus has occurred elsewhere (in Indonesia), and with other species (H. antonii, H. theivora). An increase in this phenomenon can be expected in the humid tropics, as well as an increase in a damage, as in the case of cotton in Africa. Chemical control (using lindane) is effective only with a 4-wk interval between 2 successive treatments.