Hemimetabolous Species Research Articles

Herbivory in holometabolous and hemimetabolous insects: contrasts between Orthoptera and Lepidoptera

Adaptation to a phytophagous diet involves physiological compromises that may be influenced by developmental constraints. In this review, we compare patterns of hostplant utilization with respect to nutrition and allelochemistry in representative holometabolous (lepidopteran) and hemimetabolous (orthopteran) species in order to identify those potential constraints. Overall in Lepidoptera greater molting efficiency and gut permeability, which enhance nutritional efficiency, result in higher exposure to allelochemicals and are associated with greater activity and inducibility of cytochrome P450 monoxygenase detoxication enzymes. In contrast, in Orthoptera, relative impermeability to allelochemicals due to the peritrophic membrane and cuticular sclerotization is associated with reduced nutritional efficiency and lower detoxication enzyme activity.

De novo biosynthesis of linoleic acid in insects

The de novo biosynthesis of linoleic acid was demonstrated in 8 of the 32 insect species examined, which include members of three orders and encompass both holometabolous and hemimetabolous species. The incorporation of [1- 14C]acetate into linoleate was demonstrated by radio-GLC, and in selected species by radio-HPLC, silver nitrate thin-layer chromatography, radio-GLC and GLC linked to mass spectrometry of ozonolysis products. In most of the species which synthesized linoleate, there was a time-dependent increase in the incorporation of [1- 14C]acetate into linoleate from 2 to 24 h, and most of the labeled linoleate was recovered in the phospholipid fraction. There was no readily discernable evolutionary, physiological or nutritional pattern in the ability of certain species to synthesize linoleate.

Leg regeneration in insects: An experimental analysis in Drosophila and a new interpretation

Fragments from prospective distal regions of Drosophila male foreleg imaginal discs failed to undergo proximal intercalary regeneration across leg segment borders when mechanically intermixed and cultured for 8 days with various fragments from prospective proximal disc regions. The failure of the distal cells to regenerate proximal leg segments was not due to a general restriction in their developmental potentials: Distal fragments, when deprived of their distal-most tips, regenerated in the distal direction at a high frequency. It is concluded that there exist in Drosophila leg discs the same restrictions with respect to regeneration along the proximodistal leg axis as had been previously observed in legs of several hemimetabolous insect species: Intersegmental discontinuities between grafted tissue pieces are not eliminated by intercalation. Based on the available evidence in hemimetabolous insects and in Drosophila, a new interpretation of the different aspects of regeneration in insect legs is offered. It is proposed that the two categories of regulative fields observed in insect legs, the leg segment fields and the whole leg field, represent the units of regulation for two fundamentally different regulative pathways that a cell at a wound edge can follow, the intercalative pathway and the terminal pathway, respectively. It is suggested that the criterion used by cells at healing wounds to choose between the two pathways is the difference in circumferential positional information between juxtaposed cells. The intercalative regulative pathway is switched on when cells with disparities in their axial positional information, or cells with less than maximal disparities in their circumferential information, contact one another. The terminal regulative pathway is triggered whenever cells with maximal circumferential disparities come into contact.