DENSITY-DEPENDENT PHYSIOLOGICAL PHASE IN A NONMIGRATORY GRASSHOPPER AIOLOPUS-THALASSINUS

Aiolopus thalassinus thalassinus (Fabricius) (Orthoptera: Acrididae) i s a non-migratory grasshopper of widespread geographical distribution, also endemic in the Tel-Arad region of the Northern Negev of Israel, where it is liable to sporadically damage agricultural crops. Periodic sampling in uncultivated 'batha' and agricultural fields, conducted d uring 1990/1991, indicate that A. thalassinus populations exhibit seas onal fluctuations in density. Local spatial and temporal distribution, within this region, are dependent on food availability. Field observa tions and laboratory studies suggest that the local population of A. t halassinus exhibits genetic heterochromy unaffected by density. The du ration of nymphal developmental is 34 days for nymphs reared in isolat ion, whereas crowded nymphs complete their development within only 21 days. No striking density related changes in gross morphometric featur es are evident, but, in adults from isolated culture, an increased abu ndance of sensilla coeloconica, presumably involved in olfactory chemo reception, may be functionally related to enhanced (23.6-fold higher) activity of nymphs reared under crowded conditions. This higher level of activity is correlated to higher levels of energy reserves in the h aemolymph - lipids and carbohydrates - and to increased respiration. F inally, the individual food consumption of nymphs from crowded culture is almost 5-fold higher than that of isolated nymphs and may increase the potential for crop damage. These results are similar to those obt ained with the migratory locust Locusta migratoria and support the hyp othesis that non-migratory grasshoppers exhibit some density-dependent physiological characteristics of locusts, but do not exhibit overt ch romatic or morphometric phase characteristics.