Oxygen consumption, water, lipid and glycogen content of early and late diapause and non-diapause larvae of the burnet moth Zygaena trifolii

Abstract

Oxygen consumption, lipid, glycogen, water content and dry weight are given for three corresponding larval diapause and non-diapause instars. At 20 °C, the respiration rates of diapause larvae were considerably lower (about 23%) than in corresponding non-diapause larvae. However, a body size-metabolism relationship could not be detected at a lower temperature (5 °C) in older diapause instars (L 4 and L 5 larvae). The O 2 consumption of diapause larvae (4th instar) was invariably different at 5 and 20 °C when measured at 30-day intervals during a 150-day period. The values were by one and a half times higher at 20 °C. A further intensified O 2 consumption at 20 °C indicated that the larvae were preparing to shed the diapause skin; the increase was again 1.5 times higher than in dormant larvae. O 2 consumption rates did not differ when groups of quiescent larvae were compared with diapause larvae at 5 °C, but an earlier timing of increased O 2 values and moulting indicated the different physiological state of the tested larvae. Diapause larvae contained more than twice as much lipid and twice the amount of glycogen as non-diapause larvae. The highest lipid and glycogen contents were detected in the small diapause larvae (L 3 stage), related to their pronounced respiratory rates. Lipid and glycogen were utilized throughout the whole diapause period. The glycogen content dropped more sharply at 20 °C compared to 5 °C, whereas only slight differences in decreasing lipid content occurred, indicating that glycogen is the more important energy source to survive the period after the onset of diapause. The calculated daily rates of loss of lipid and glycogen showed that the lipid and glycogen contents were sufficient for the L 4 larvae to survive an approx. 1 year diapause period at 20 °C. During the diapause period, the fresh weight ratio dropped more sharply than lipid and glycogen, implying that water loss was the main factor in decreasing body weight. The water content decreased to 61% of the initial value (4th instar). However, it was obviously not correlated to the invariable supercooling ability of dormant larvae.