Trehalose in tobacco hornworms, Manduca sexta : regulation during diapause and nondiapause pupal development

Regulation of trehalose synthesis in fat body of diapausing and nondiapausing larvae and pupae was studied in the tobacco hornworm, Manduca sexta. Trehalose from nondiapausing and diapausing larvae is present in fat body and hemolymph at levels 60% of those found in nondiapausing and diapausing pupae. Trehalose in fat body of nondiapausing pupae is 3 times higher than in diapausing pupae. In contrast, glucose levels in hemolymph (5 mM) and fat body (12 mM) are the same in nondiapausing and diapausing larvae and pupae. Fat body trehalose synthesis does not appear to be affected, in vitro, by high levels of exogenous trehalose or glucose. Studies of fat cell membrane permeability to glucose and trehalose in larval and pupal stages failed to elucidate how fat body maintains a higher level of trehalose than that present in hemolymph.

The onset of nondiapausing or diapausing pupal development is accompanied by both a 50% decrease (relative to larvae) in hexokinase activity and an increase, rather than a decrease, in the levels of trehalose in fat body or hemolymph. Rates of glucose incorporation into trehalose by intact fat cells, in vitro, are much lower than predicted, based on measured hexokinase activity.

Temperature influences trehalose regulation in the fat body of larvae and diapausing pupae but not in nondiapausing pupae. In the absence of exogenous pools of glucose at 25°C fat body experiences an increase in trehalose synthesis from glycogen derived precursors. At 3°C there is a contraction of the intracellular glucose pool in diapausing pupae.

I conclude that the trehalose regulatory mechanisms characteristic of silkmoths and blowflies are not operative in Manduca sexta.