Pre-and Postharvest Changes in Sweetpotato Root Surface Chemicals Modulating Insect Resistance

Levels of major root surface components for two sweetpotato [Ipomoea batatas (L.) Lam.] cultivars that differ in susceptibility to the sweetpotato weevil [Cylas formicarius elegantulus (Summers)] were determined. Analyses were made 30 days before harvest, at harvest, after curing, and after 2 months of storage during two seasons. Significant variation in the amounts of individual components, especially boehmeryl acetate, which is known to be an ovipositional stimulant for the weevil, was found before and after harvest, with season, and between cultivars. These results suggest that variation in field susceptibility of cultivars displaying moderate levels of resistance may be due in part to seasonal variation in the level of ovipositional stimulants.

TEMPERATURE RELATIONS OF ADULT COLEOMEGILLA MACULATA LENGI AND C. M. MEDIALIS (COLEOPTERA:COCCINELLIDAE) AND RESPONSES TO OVIPOSITIONAL STIMULANTS

An adult of either Coleomegilla maculata lengi or C. m. medialis ate about 280 mg dry Acyrthosiphon pisum in its lifetime at various constant temperatures. Total food consumption and rate of intake increased with temperature and rate did not vary with age. The average ages attained by field-collected and laboratory-reared adults were greatest at temperatures of 17° and 23 °C, respectively, for C. m. lengi and at 23 °C for C. m. medialis. Neither subspecies laid any eggs at 17 °C, C. m. lengi laid some eggs at 23 °C, and both subspecies laid the largest number of eggs at 25 °C. Fertility as percentage of eggs hatched was lower in both subspecies at 34 °C (30%) than at 23° and 25 °C (100%). Ethanol extracts of teak, cinnamon, clove, guaiacol, and resorcinol were the most effective ovipositional stimulants for C. m. lengi when formulated in water. Exposure to the ethanol extracts of different plants increased the incidence of oviposition by 19% and the number of eggs/♀/day by 36% in C. m. lengi.