ONTOGENIC AND ENVIRONMENTALLY-INDUCED CHANGES IN CUTICULAR HYDROCARBONS OF ORYZAEPHILUS-SURINAMENSIS (COLEOPTERA, CUCUJIDAE)

The influence of short-term environmental challenges such as desiccati on and temperature extremes on the cuticular hydrocarbon composition o f insects is not well understood. We report here the effects of chilli ng (4 degrees C), exposure to moderate relative humidity (approximate to 30%), and exposure to dusts of silica gel, cliatomaceous earth, and freeze-dried, ice-nude ating bacteria (Pseudomonas syringae) on the c uticular hydrocarbons of larvae and adults of the sawtoothed grain bee tle, Oryzaephilus surinamensis (L.), a major pest of stored grain. Lar vae and adult beetles have some hydrocarbons in common (particularly n -alkanes and small quantities of internal methyl branched alkanes), bu t they differ substantially in alkene composition. Unstressed larvae h ave approximate to 4% of Z-(9)-alkenes (C-25 to C-31) and 1% of a homo logous series of Z,Z-(6,9)-dienes of the same chain lengths. Adult bee tles, however, in unstressed situations have none of the larval dienes on their cuticle, and possess only approximate to 3% of the Z-(9)-mao noenes. When the adult beetles there environmentally stressed for 24 h , they released up to 3% of phenotypically larval dienes onto their cu ticle. In addition, desiccation stresses resulted in adults substantia lly increasing the quantity of monoenes on their cuticle (up to 5% of the total), whereas low temperature caused them to reduce the quantity of monoenes. Larvae exposed to similar stresses did not increase the quantity of dienes on their cuticle, but rather decreased their alkene s and increased the abundance of alkanes. The release of the dienes by the adults was shown not to be from new biosynthesis, but rather to r esult from release of stored dienes. The physiological and ecological ramifications of these changes in cuticular hydrocarbon profile by the various life stages of the sawtoothed grain beetle in response to env ironmental stresses are discussed.