Abstract

A study was made to test the hypothesis that the teak defoliattor, Hyblaea puera Cramer(lepidoptera, hyblaeidae) outbreaks begin in small epicentres and spread progressively to extensive areas as a result of population built up in these epicentres. To gather relevant data, about 10, 000 ha each of teak plantation at Nilambur and Konni were kept under observation during the outbreak period in 1993 and all outbreaks mapped. Interpretation of the spatial and temporal sequence of outbreaks yielded the following conclusions. In large teak plantation areas, H.puera outbreaks begin in comparatively small epicentres which may be 0.6 to 12 ha in area. These epicentres are not constant over the years and do not represent highly favourable local environemnts.Instead, they are sites where a group of immigrating moths or moths locally present but concentrated by as yet unknown phenomena assemble and lay eggs. Although many of the extensive outbreaks which occured subsequently could be attributed to locally built up population. Immigration of moths from outside the Nilambur area necessary to explain these. It appears that many of the large scale outbreak can be prevented by controlling the small epicentre populations. However, the involvement of immigrating moths cannot be ruled out. An experimental study involving control of epicentre populations is recommended to examine the effectiveness of this approach to teak defoliator management. The study also revealed that teak plantation in all areas are not equally prone to defoliator attack. Incidence of outbreak appears to be strongly correlated with orographic features of the planted area, but more detailed studies are needed to elucidate the relationship