Regulation of taste thresholds in the blowfly, Phormia regina Meigen, was investigated by manipulating the nutritional status of the insect and determining the effect on labellar and tarsal taste thresholds. Two feeding paradigms were employed: single meals administered to hungry flies, and ad libitum feeding of aqueous sucrose solutions for 4–5 days.
Flies which had fed on aqueous sucrose for several days exhibited high labellar and tarsal thresholds, with tarsal thresholds always higher than labellar thresholds. Food deprivation caused labellar and tarsal thresholds to decline. There was a positive logarithmic relationship between crop mass and labellar or tarsal thresholds. Consumption of single meals of aqueous sucrose caused increases in labellar thresholds similar to those for tarsal thresholds.
Labellar thresholds in flies fed ad libitum were not affected by transection of the recurrent nerve (RN) or the median abdominal nerve (MAN). Tarsal thresholds, in contrast, were markedly attenuated by RN transection but not by MAN transection. Transection of the RN in hungry flies prior to feeding them a single meal did not prevent the normal post-prandial rise in labellar thresholds. In earlier experiments, RN transection has been shown to attenuate the post-prandial rise in tarsal thresholds.
It appears that labellar and tarsal thresholds in the blowfly are similarly affected by consumption of aqueous sucrose. However, inhibitory feedback from the RN, which is partially responsible for elevation of tarsal thresholds after a meal, does not affect labellar thresholds. Additional, still unidentified, factor(s) may regulate both labellar and tarsal thresholds.