Spatial dynamics of teak defoliator (Hyblaea puera Cramer) - Cochin ...

light-trap. A total of 596 moths were collected on days preceding the start of
this outbreak. Locally emerged moths were present during this period. No
moths were collected prior to the last outbreak which was 0.05 km away from
the trap and which extended to 435.3 ha. There were no locally emerged
moths during the period.
It can be seen that out of seven outbreaks which occurred during the
study period, occurrence of two outbreaks (s1.nos. 2 and 7) could not be
detected by light-trap catch eventhough the sites infested were very close (0.5
and 0.05 km respectively) to the trap. Very few moths were collected during
the 4 th and 5 th outbreaks (l and 9 respectively) which also occurred near to the
light-trap (0.5 and 0.05 km respectively). Only the occurrence of three
outbreaks (s1.nos. 1,3 and 6) among the total seven was well indicated by trap
catch. Majority of moths were collected during the l" and 6 th outbreaks (145
and 596 respectively) during which moths were emerging locally from earlier
outbreaks. Only the occurrence of the third outbreak was well indicated (74
moths were collected) by trap-catch when no locally emerged moths were
present. Thus when no locally emerged moths were present, only one of the
five impending outbreaks was predictable by a high trap catch.
7.4. DISCUSSION
This study indicates that eventhough the moths were collected in the
light-trap during the period of the year when teak defoliator outbreaks are
prevalent, it does not always collect moths, which arrive in the plantation for
egg laying. Large number of moths was collected while they were emerging
from the plantations nearby. But the trap was unable to attract and collect
moths every time they arrived at the plantation for egg laying. The reason is
not well understood but it appears that the moth aggregation that arrives for
egg laying respond primarily to the chemical signals from the host plant.
This study has shown that the light-trap cannot be relied upon as an
outbreak detection device. Detection of an outbreak needs ground
observations. These observations can be limited to areas, which have tender
84