Before the trap crop emerged, only four male rats were
trapped. However, during the field operations period, 70%
of the trapped rats were females. This indicates the potential
for a high rate of increase in population size after the
establishment of food sources and commencement of
breeding. The first pregnant rat trapped was recorded
within a month after crop establishment. Of the 32 female
rats caught from 13 February to 30 March 2002 (tillering
stage), nine were pregnant. They were dissected and
yielded a total of 74 foetuses. Although the proportion of
female rats declined during seeding to the maximum
tillering stage, there were still more females (58%) than
males (42%). Thereafter, more males than females were
trapped (Figure 1).
Before the trap crop emerged, only four male rats weretrapped. However, during the field operations period, 70%of the trapped rats were females. This indicates the potentialfor a high rate of increase in population size after theestablishment of food sources and commencement ofbreeding. The first pregnant rat trapped was recordedwithin a month after crop establishment. Of the 32 femalerats caught from 13 February to 30 March 2002 (tilleringstage), nine were pregnant. They were dissected andyielded a total of 74 foetuses. Although the proportion offemale rats declined during seeding to the maximumtillering stage, there were still more females (58%) thanmales (42%). Thereafter, more males than females weretrapped (Figure 1).
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