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

Table 4.9. Elevation and aspect ofthe first outbreak sites at Kariem Muriem in the
years 1992-1994.
Year Elevation Aspect
(mts.) (degrees)
1992 70.8 ± 3.1 284 ± 41
1993 75.7 ± 19.2 247 ± 73
1994 51.9±10.1 288 ± 50
It can be seen that the site of occurrence of first outbreak in 1994 was an area that
had the first outbreaks in 1992 and 1993. Small patches occurred outside this area
in 1992 and 1993. Generally, these sites had a mean elevation ranging from 50-75
metres and mean aspect ranging from 247-288 degrees. Ifthe relationship between
susceptibility to defoliation and topography were known, it would greatly reduce
the area to be monitored for identifying initial outbreaks. Observations at other
teak growing areas are needed to generalize these findings.
4.4. DISCUSSION
The pattern of defoliator incidence in all the three years indicated that the
outbreaks were not randomly distributed in space. It was observed that in all the
three years, sites having the highest outbreak frequency value were surrounded by
an area with the next lower frequency value. Spatial autocorrelation indices of the
outbreak frequency maps indicated that the high frequency sites occur in a
clustered manner. This indicates that some sites are more prone to defoliator
attack. This is similar to the spatial pattern exhibited by the Gypsy moth
(Lymantria dispar L.) defoliation (Liebhold and Elkinton, 1989).
The temporal sequence of outbreaks given in Tables 4.2, 4.3, and 4.4 shows
that the outbreaks which occur during any year are not always caused by
generations of the insect breeding in the same area. Out of the total of eight
outbreaks in 1992, only those on 7 July, 6 August, 22 September, and 14 October
could have been caused by moths emerging from the same area. The only possible
cause for the other four outbreaks is the immigration ofmoths into the study area.
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