Biological activity and binding site characteristics of the PA1b Entomotoxin on insects from different orders.

The aim of this work was to investigate both the biological activity of an entomotoxin, the pea albumin 1b (PA1b), and the presence or absence of its binding site within an array of insect species. The data obtained showed that insect sensitivity was not related to its taxonomic position. Moreover, PA1b was not toxic to several tested microorganisms. However, the binding site was found to be conserved among very different insects, displaying similar thermodynamic constants regardless of the in vivo species sensitivity. The binding site alone was, therefore, not sufficient for toxicity. One exception was the pea weevil, Bruchus pisorum, which was the only tested species without any detectable binding activity. These findings indicate that the binding site probably has an important endogenous function in insects and that adaptation to pea seeds resulted in the elimination of the toxin binding activity in two independent insect lineages. Other mechanisms are likely to interact with the toxin effects, although they are still largely unknown, but there is no evidence of any specific degradation of PA1b in the midgut of insects insensitive to the toxin, such as Drosophila melanogaster or Mamestra brassicae.

Carcass analysis to improve a meat-based diet for the artificial rearing of the predatory mirid bug Dicyphus tamaninii.

Improvement of an existing meat-based diet has been obtained for rearing the generalist predator Dicyphus tamaninii (Heteroptera: Miridae). The approach followed, different from the classical addition/deletion method, was performing biochemical analysis of adult carcasses in order to have information about the nutritional status of the predator. Comparison of total, free amino acids and lipid composition of meat-reared and conventionally reared females allowed detecting some nutritional deficiencies. A reformulated diet with new sources of proteins and lipids was tested again with the predator. Some biological parameters of bugs that were inferior in the initial meat diet when compared with those of the conventionally reared insects, such as nymphal development time and fresh weight, have been improved with the reformulated diet.

Nutritional plasticity of the predatory ladybeetle Harmonia axyridis (Coleoptera: Coccinellidae): comparison between natural and substitution prey.

The predatory coccinellid Harmonia axyridis is a polyphagous species, efficient at controlling certain aphid species and already commercialized in Europe for that purpose. The complete development of this predator can be accomplished using the aphid Acyrthosiphon pisum or Ephestia kuehniella eggs as substitution prey. Biochemical analyses were conducted on the proteins, lipids, and carbohydrates of these two different prey species. E. kuehniella eggs were 2 times richer in amino acids than A. pisum adults (12% of the fresh weight vs. 6%). E. kuehniella eggs were 3 times richer in lipids than the aphids but, on the contrary, the aphids were 1.5 times richer in glycogen. The impact of these two kinds of food on the body composition of the coccinellid was evaluated to appreciate the degree of nutritional plasticity of the coccinellid. The composition of the coccinellids feeding either on E. kuehniella eggs or on aphids was compared for amino acid, fatty acid and glycogen contents, revealing a good capability of H. axyridis to develop on foods that are very different in their biochemical composition. Nevertheless, when fed on aphids, the crude protein content of the predator was reduced and the lipid content decreased by a factor of two, with a change in amino and fatty acid patterns. Some biological parameters, such as larval mortality, adult weight, and fecundity, were modified according to the food eaten.