Relationship between tissue-specific hydrocarbon profiles and lipid melting temperatures in the cockroach Blattella germanica

Hydrocarbons (HC) are the most important waterproofing barrier on the cutic le of most terrestrial insects. Yet, the relationships among the type, amou nt. biophysical properties, and water retardation capacity of constituent H C are poorly understood. Melting temperatures and gas chromatographic profi les of HC of German cockroach tissues of various ages and stages were compa red. The melting temperature (T-m) of oothecal HC was highest, T-m of epicu ticular HC was substantially lower, and that of hemolymph HC was lowest. Th e epicuticular HC of older nymphs and adults had higher T-m than HC of the same sex and stage soon after the molt. The HC of females had higher T-m th an did male HC. Principal components analysis suggested that normal and 3- and 5-methylalkanes, which were more prevalent on the epicuticle, were asso ciated with higher T-m, implicating these components of the HC blend in wat erproofing roles. The cockroach ootheca is particularly well protected by a n abundance of n-alkanes and its external HC exhibit the highest T-m of any HC blend. The methyl ketone sex pheromone components, which are derived fr om HC, appear to only slightly reduce the T-m of the epicuticular HC, proba bly because the methyl ketones represent only 1.12% of the mass of epicutic ular HC. We suggest that the evolution of polar epicuticular chemical signa ls may be constrained by their tendency to increase water transpiration.