The activity and number of protocerebral neurosecretory neurons of the dorsolateral group (L1, L2 and L2'), as well as the size of the corpora allata were investigated in 5th instar larvae of the gypsy moth (Lymantria dispar) from two populations (oak and locust-tree forests) fed one of two host-plants (oak is a suitable and locust-tree an unsuitable host-plant).
The monitoring of activity related cytological parameters and the number of protocerebral dorsolateral neurosecretory neurons revealed that differently adapted populations respond to nutritive stress differently. The activity of the L1 neurosecretory neurons in the protocerebra of the caterpillars is low in those from the locust-tree forest regardless of host-plant quality. The L2 neurosecretory neurons in the oak population become active when they were fed the unsuitable host-plant whereas their activity was high in locust-tree caterpillars regardless of the host-plant. A decrease in the number of neurosecretory neurons in a response to a novel food was noticed in both populations. The activity of the L2' neurosecretory neurons was similar in all caterpillars, but their number was increased in those from the locust-tree forest. The corpora allata of the locust-tree caterpillars were large whereas those of the oak forest caterpillars only increased in size when they were fed locust-tree leaves.
It is obvious that nutritive stress results in neurosecretory reorganization and changes in the titre of hormones that modulate the morphogenetic programme.
While most theoretical models for the evolution of ageing assume that duration of pre-adult development does not affect the longevity, experimental data are still controversial and inconsistent. Here we examined the short-term and long-term pattern of pre-adult development time and longevity in populations of the gypsy moth (Lymantria dispar) originating from either oak forest (Quercus petrea), a suitable, or locust-tree forest (Robinia psedoacacia), a poor habitat. Using a full-sib design, we examined the genetic correlations between traits found in larvae reared on oak or locust-tree leaves. We detected only negative and insignificant genetic correlations, except for males from the Robinia population reared on oak leaves where the correlation was negative and significant. Our results also showed that a population living 40 generations in the locust-tree forest exhibited a significantly higher longevity than the Quercus population, whereas a significant difference between these two populations in pre-adult development time does not exist. The results are discussed in relation to the potential effect of stress selection in moulding the longevity of the gypsy moth.
A study on the effect of heat stress on the activity of the medial A1 and A2 neurosecretory neurons (NSN), and the activity of midgut a-amylase and protease was performed on the fifth larval instar of Morimus funereus. Exposure of the larvae to 35°C led to a decrease in the activity of both A1 and A2 NSN, the former being more marked than the latter. These neurons responded differently to heat stress in terms of neurosecretory material synthesis and release. The changes in the size of both A1 NSN and their nuclei and protease activity in the larvae exposed to elevated temperature were significantly correlated, which suggests that A1 NSN play a role in the regulation of the activity of this enzyme during heat stress. The significant correlations between the size of A2 NSN and protease activity in the controls, and the size of both A2 NSN and their nuclei and amylase activity in larvae exposed to heat stress, similarly may mean that A2 NSN regulate both digestive enzyme activities depending on environmental temperature.