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EN
Density dependent responses of 4th, 5th and 6th instar gypsy moth larvae were studied at the level of larval mass, midgut loading and activities of three digestive enzymes (alpha-amylase, trypsin and leucine aminopeptidase). High density significantly reduced larval mass while midgut loading (expressed as relative midgut mass) did not change except in the 5th instar where it was increased at high density. Specific amylase and leucine aminopeptidase activities were not affected by crowding. Specific trypsin activity was on average higher in crowded than in isolated larvae. High density also affected the correlations between midgut protein content and activities of two proteolytic enzymes suggesting differences in regulatory mechanisms of insect digestion. The importance of these changes for survival under stressful conditions is discussed.
EN
Lipase activity of the gypsy moth (Lymantria dispar L.) was studied by the spectrophotometric method using crude homogenate of fifth-instar larval midgut tissues as the enzyme source and p-nitrophenyl caprylate (pNPC) as substrate. A Km value of 0.310mM and a Vmax value of 1.479U/mg prot. were obtained for this substrate. Among various p-nitrophenyl esters tested, maximum activity was obtained for p-nitrophenyl caprylate and p-nitrophenyl caprate. The enzyme was most active at alkaline pH, with maximum at pH 8.2. Decreased activity was detected after preincubation in buffers of pH below 7.0 and above 8.2. The enzyme was unstable at room temperature. The enzyme was Ca2+ independent. Its activity was inhibited by PMSF, Fe2+, Ag+ and Pb2+, while Fe3+ inhibited enzyme activity by about 40%.
EN
To assess local differentiation in host preference, a two-choice test was performed on firstinstar gypsy moth larvae originating from an oak and locust-tree forest. More than 40 generations feeding on locust-tree leaves, rich in alkaloids, led to non-efficient discrimination of host leaves in larvae from a locust-tree forest. Possible causes of observed population differences are discussed in the present paper.
EN
Sexual differences in reaction norms of life history traits (larval development time-LDT, pupal weight-PW and adult longevity-L) were investigated in the gypsy moth reared on young or old oak leaves during the first larval instar. Sexual dimorphism was revealed for genetic variation in reaction norms that was expressed only for LDT in males, and PW and L in females. Higher mean plasticity of longevity was found in males compared to females indicating that the sexes are exposed to divergent selective pressures. Greater dependence of males on energy resources (carbohydrates and lipids) may account for the observed differences.
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