Biosynthesis of hydrocarbons and contact sex pheromone and their transport by lipophorin in females of the German cockroach ( Blattella germanica)

Abstract

The sites of synthesis, and transport of hydrocarbons and methyl ketone contact sex pheromone, were examined in the German cockroach. The abdominal integument of 7-day old Blattella germanica females showed linear incorporation of [1- 14C]propionate into hydrocarbon and pheromone for at least 4 h in vitro, whereas other body parts including the head, wings, legs, thorax, fat body, digestive tract, and vitellogenic ovaries produced negligible amounts of hydrocarbon and pheromone. The sternites synthesized significantly more hydrocarbon and methyl ketones than the tergites, and in both, the incorporation of propionate into hydrocarbon correlated well with its incorporation into the methyl ketone pheromone, suggesting that the abdominal oenocytes or epidermal cells synthesize both hydrocarbon and pheromone. The abdomen contained about 55% of the total hydrocarbon and pheromone in the female, and both were located mainly in the ovaries, integumental epidermal cells (including oenocytes), fat body, and hemolymph. Hemolymph contained up to 20% of the internal hydrocarbons and their methyl ketone derivatives, suggesting that hemolymph carries and circulates hydrocarbon and pheromone in the female. A high density lipophorin (1.109 ± 0.002 g/ml) was isolated and purified from hemolymph by KBr gradient ultracentrifugation and was shown to be the only hemolymph protein that carries hydrocarbon and pheromone. This result suggests that lipophorin loads newly synthesized hydrocarbon and pheromone from the abdominal epidermis and transports them to various tissues, including the ovaries, fat body and possibly the epicuticle. After injection of radiolabeled propionate, newly synthesized radiolabeled methyl-branched hydrocarbons appeared first in the epidermal fraction (with oenocytes) and hemolymph, and later on the epicuticle. When veins entering the fore-wings were cut so that hemolymph circulation to the wings was blocked, the amount of newly synthesized hydrocarbon on the wings was significantly lower than on intact fore-wings. Significantly more radiolabeled hydrocarbon which had been topically applied on the sternites was recovered in the hemolymph than on the surface of the wings. These results show that transport of hydrocarbon is mediated by lipophorin, which shuttles newly synthesized hydrocarbon and methyl ketone sex pheromone from the abdominal oenocytes to epicuticular and internal deposition sites, including the ovaries.