Date of Award

1986

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Entomology

Abstract

Velvetbean caterpillars, Anticarsia gemmatalis Hubner, were reared at different densities on soybean. The degree of dark pigmen- tation was density-dependent under field and laboratory conditions. The highest degree of dark pigmentation was expressed in the last instar when larvae were crowded throughout development. Soybean plant age had no effect on the degree of dark pigmentation. Larval development was delayed and one-day-old adult weight was decreased as the larval density and plant age increased. Size and biochemical composition of one-day-old A. gemmatalis adults was investigated in relation to larval pigmentation, larval den- sity and plant age. Wet, dry and protein weights of adults declined with increases in larval pigmentation, larval density and plant age but these factors did not affect carbohydrate and lipid weights. The observed linear relationships between adult weight and the protein or lipid weights reflect the size-dependent nature of nutrient accumulation by the larvae. Hemolymph concentration of carbohydrate in A. gemmatalis adult females decreased to a level of no further change after 60 min of flight. Total fatty acid concentration in the hemolymph increased during the first 30-60 min of flight and then declined to preflight levels. After four hours of flight, whole body lipid content had not changed but whole body carbohydrate was reduced 77.4%. These observations suggest that lipid is utilized more efficiently than carbohydrate during A. gemmatalis flight. Growth and development of cumulatively aged A. gemmatalis larvae were characterized on the basis of weight, instar and gate. Using this information, criteria were developed for the selection of synchronous last instar larvae with 94.5% certainty. The ability to obtain synchronous larvae enabled last instar development to be related with hemolymph titers of juvenile hormone esterase (JHE) activity, alpha-naphthyl acetate esterase activity and protein concentration. Phase variation in size, pigmentation and development of A. gemmatalis was investigated in relation to density and juvenile hormone (JH) application. Increasing the JH level of crowded larvae resulted in larvae that were similar to uncrowded larvae in color, developmental rate, size and JHE activity. These results suggest that the JH titer of crowded A. gemmatalis larvae is lower than uncrowded larvae.

Pages

154

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