Date of Award

1996

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Richard N. Story

Abstract

The biology and ecology of the yellowmargined leaf beetle, Microtheca ochroloma Stal, were studied on cabbage, Brassica oleracea var capitata L., collard, B. oleracea var acephala L., mustard, B. juncea Cosson, turnip, B. rapa L., and radish, Raphanus sativus L. The life cycle of the beetle consists of an egg stage, four larval instars, prepupal, pupal and adult stages. There were no significant differences in the effect of host plant on duration of development of immature beetles (p = 0.3353). The mean duration of development from oviposition to adult emergence ranged from 26.6 d on turnip to 27.5 d on cabbage. There was however a significant effect of host plant on multi-generation survivorship. Beetles reared on cabbage did not survive beyond the second generation. With respect to adult beetles, significant differences were found in the effect of host plant on fecundity (p = 0.0057) and longevity (p = 0.0001). The mean fecundity of females was significantly higher for beetles maintained on turnip (490.74 $\pm$ 116.04) than for those maintained on collard (198.85 $\pm$ 28.94). There were no significant differences in the mean fecundities of females maintained on cabbage (271.25 $\pm$ 39.11), mustard (424.95 $\pm$ 46.39) and radish (440.05 $\pm$ 50.09). Beetles fed radish lived significantly longer than beetles fed each of the other host plants. There were no significant differences in the longevity of male and female beetles by host plant. In choice tests for feeding preference, both the third larval instar and adult beetles showed strong preference for the foliage of turnip and mustard. Collard and cabbage were least preferred. Susceptibility of beetle larvae to insecticides was esfenvalerate $>$ carbaryl $>$ malathion. There were no significant differences in the effects of host plant on susceptibility of the larvae to the insecticides. There was however a 10-fold difference in the activities of glutathione S-transferases enzymes for beetle larvae fed collard and those fed turnip. Spatial distribution studies revealed that both immature and adult beetles have aggregated spatial patterns on field planted mustard.

ISBN

9780591034998

Pages

127

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