Development of cabbage webworm, Hellula undalis (Fabr.) on head cabbage, Brassica oleracea var. capitata

A. Sivapragasam

Abstract

The development and basic population parameters of Hellula undalis, a major pest of head cabbage, Brassica oleracea var. capitata were determined in both the laboratory and field trials. There was a significant difference in the incubation period between the laboratory and field being 3.25 days and 3.00 days, respectively. However, there was no difference in egg hatchability in the two environments being 91.3% (laboratory) and 93.0% (field). The insect generally underwent five larval instars and the mean larval period was significantly shorter in the laboratory (9.76 days) compared to the field (12.57 days). Larval survival was higher (92.5%) in the field than in the laboratory (68.2%). In the laboratory, the mean duration of the pupa was significantly longer (7.6 days) than in the field (6.3 days). The total developmental period, from egg to adult emergence, was significantly shorter (20.5 days) in the laboratory than in the field (23.6 days). The survival rates from egg to adult emergence were 49.8% and 16.2% in the laboratory and field, respectively. The sex ratio (female-male) of the adults in both environments did not differ significantly from the ratio of 1:1. The mean adult longevity did not differ significantly for adults of both sexes (6.93 and 6.34 days for male and female, respectively) reared in the field and those in the laboratory (5.61 and 5.38 days for male and female, respectively). The survivorship curve for the laboratory population for both sexes resembled the Slobodkin’s Type III whereas those from the field resembled a Type II. Significantly, numerically higher number of eggs was laid by laboratory females than those from the field. The net reproductive rate (Ro), mean generation time (G), intrinsic rate of increase (r_m), the finite birth rate (b) and the instantaneous birth rate (b) were also higher for laboratory populations than those from the field.

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