Cuticular hydrocarbon synthesis in relation to feeding and developmental stage in nymphs of Blattella germanica (Dictyoptera: Blattellidae)

Abstract

The pattern of hydrocarbon synthesis aad transport to the epicuticle were examined in males and females of the German cockroach, Blattella germanica (L.), during the last nymphal stadium. Methods used to extract hydrocarbon form insects were validated in detail. A double hexane extraction for cuticular hydrocarbons and a triple chloroform-methanol extraction of homogenized insects for internal lipids removed essentially all hydrocarbon from the respective compartments, whereas the external extraction did not remove hydrocarbon from the interior of the insect. Synthesis in vivo was measured by the incorporation of [1-14C]propionate into methyl-branched hydrocarbon at 2-d intervals throughout the stadiam. In both sexes, hydrocarbons were synthesized at increasing rates during the first 2/3 of the stadium, then synthesis ceased 2 d before the imaginal molt. Hydrocarbon synthesis was related to stage-specific food intake in both male and female nymphs. A declining proportion, but relatively constant quantity, of newly synthesized hydrocarbon was transported to the epicuticle as the nymph progressed through the intermolt period. The majority of the newly synthesized hydrocarbon at all ages was retained internally, however, suggesting that they serve as a source of epicuticular and ovarian hydrocarbon in the adult. Gas-liquid chromatography confirmed the patterns of hydrocarbon synthesis and showed a greater accumulation of hydrocarbons internally than on the nymphal epicuticle. Early in the last stadium, the majority of internal hydrocarbon is in hemolymph, whereas late in the stadium the fraction of internal hydrocarbon in the hemolymph declines, presumably as newly synthesized hydrocarbon begin to associate with fat body and the developing limaginal cuticle.