VARIATION IN ATTACK BY THE MAHOGANY SHOOT BORER, HYPSIPYLA-GRANDELLA (LEPIDOPTERA, PYRALIDAE), IN RELATION TO HOST GROWTH AND PHENOLOGY

In order to evaluate the relationships between attacks by the mahogany shoot borer Hypsipyla grandella (Zeller) and host growth and phenolog y, field trials of Spanish cedar Cedrela odorata and American mahogany Swietenia macrophylla established in Costa Rica were assessed intensi vely over an 84 week period. Height growth of C. odorata was approxima tely twice that of S. macrophylla, with mean growth rates of 2.0 and 1 .3 cm week(-1) respectively. Cedrela odorata displayed pronounced temp oral variation in leaf phenology, with a minimum of 51% of trees in le af during a relatively dry period. In contrast, the minimum proportion of foliated S. macrophylla trees was 87%. No shoot borer attacks were recorded on S. macrophylla until week 50 after the onset of assessmen ts, whereas initial attacks of C. odorata were recorded during week 6. By week 84, the proportion of trees attacked was 74% and 77%, respect ively. In both species, attacks were concentrated in seasonal peaks, c oinciding with the production of new shoots. Pronounced spatial variat ion in attack was observed in both species. At week 12, the number of attacks per block in C, odorata was negatively correlated with availab le calcium concentration (r = 0.85, P < 0.001), whereas mean height gr owth of C. odorata was positively correlated with available phosphate concentration (r = 0.84; P < 0.001). Significant variation in height t o first damaging attack was observed in both species. By the end of th e observational period, only 6% of C. odorata and 0.4% S. macrophylla remained undamaged to a height of 3 m. It is suggested that control me thods for the mahogany shoot borer should take account of temporal dyn amics in attack, and relationship to host phenology. Manipulation of t he soil nutrient status may also form part of an integrated approach t o pest management.