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In the stream-dwelling isopod Lirceus fontinalis, males and females engage in a precopulatory mate guarding phase prior to mating. We examined the energetic costs of mate guarding behavior in males by separately assaying glycogen and lipid content at different time increments following mating. We found that males that had recently mated possessed reduced glycogen reserves and that these reserves were fully replenished within 36 h. Conversely, we found that male lipid reserves were unaffected by time since mating. We concluded that precopulatory mate guarding behavior is energetically costly to males and that glycogen is the energy source utilized to pay that cost. We also examined whether food deprivation during the mate guarding phase affected male energy reserves (glycogen) at the end of that phase. We found that males that were held in the laboratory and starved during mate guarding possessed reduced glycogen at the termination of the phase when compared to fed males. This reduced quantity was equivalent to the glycogen reserves of recently mated males collected from the field. We propose that food deprivation during the mate guarding phase explains the reduction in glycogen reserves at the termination of that phase. We discuss these results with reference to patterns of refuge use behavior during the mate guarding phase.

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Ecdysone 20‐monooxygenase is the insect cytochrome P‐450 dependent steroid hydroxylase system responsible for the conversion of ecdysone to 20‐hydroxyecdysone. Using an in vitro radioassay, the levels of ecdysone 20‐monooxygenase activity were quantified during embryogenesis in the egg, and in the fat body and midgut tissues during the fourth larval, fifth larval, and pupal‐pharate adult stadia of the tobacco hornworm Manduca sexta. Although basal, ecdysone 20‐monooxygenase activity was detected during the latter stages of larval embryogenesis. Postembryologically, a single major peak or increase was detected in both fat body and midgut tissues during each stadium. In the fourth larval instar, both fat body and midgut ecdysone 20‐monooxygenase activities were found to peak in the latter half of the stadium at the time of spiracle apolysis; both activities dropped to basal levels by the time of ecdysis. During the fifth larval stadium, fat body steroid hydroxylase activity was found to rise during the feeding stage (days 1–4), then dropped back to basal levels by the onset of pharate pupal development on day 7 of the stadium. Midgut monoooxygenase activity during the fifth larval stadium, however, remained basal during the feeding stage, then rose dramatically to peak on day 5 with the onset of wandering, then dropped back to basal levels by the onset of pharate pupal development. Both fat body and midgut hydroxylase activities were basal during the pupal stage and only rose late in pharate‐adult development, just prior to adult eclosion. Arch. Insect Biochem. Physiol. 41:24–32, 1999. © 1999 Wiley‐Liss, Inc.