Utilization of lipid for flight and reproduction in Spodoptera litura (Lepidoptera: Noctuidae)

Abstract

Research of the physiological traits of a long-distance migratory insect, the common cutworm Spodoptera litura, in relation to flight and reproduction, was focused on triacylglycerol (TG) levels and their fatty acid composition.Tethered flight experiments demonstrated that three-day old male moths can fly more than 20 h. Among eight identified fatty acids of which the adult TG is composed, the ratios of the following unsaturated fatty acids, palmitoleic acid (C 16:1), oleic acid (C 18:1), linoleic acid (C 18:2) and linolenic acid (C 18:3), gradually declined with longer flight duration. On the other hand, the TG levels of non-flown males reared for ten days on only water, were the same as those of three-day old males after 12 hr of flight, but the ratios of these unsaturated fatty acids in TG's remained nearly unchanged. These results suggest that the unsaturated fatty acids in TG are mainly used as a flight energy source.As ovarian development in females of this species occurs shortly after adult emergence, long-distance migratory capacity has been regarded as highly unlikely. In fact, ovarian development was completed within three days after adult emergence and females laid eggs thereafter. During this three day period TG increased in the ovary, accompanied by increasing ratios of unsaturated fatty acids in the TG's and the ovary eventually occupied most of the abdomen, in spite of a nearly constant level of TG in the abdomen and unchanged ratio of its unsaturated fatty acids. These facts support the transfer of TG from the fat body to the ovary, and further suggest that the mature females utilize the TG deposited in the ovaries as a flight energy source. Then if they migrate a long distance, they use residual TG after flight for egg production.

Keywords

• spodoptera litura
• triacylglycerol
• flight energy
• fatty acid
• migration