Quality control of Harmonia axyridis (Pallas) (Coleoptera Coccinellidae) fed on liver-based artificial diets

Harmonia axyridis is a polyphagous coccinellid feeding mainly on aphids. Originating from Asia, this species was introduced in many countries in America as well as in Europe, and is sometimes considered as an invasive species. The high predation capacity of the species is an advantage for biological control strategies. Several artificial diets have been already tested, but the quality of the predators produced has rarely been tested. This predator could be reared from first instar larva to adult on a pork liver-based artificial diet, which also proved to be suitable for allowing adult survival and reproduction. Biological and biochemical parameters (carcass analyses) of a flightless strain of H. axyridis, fed on this artificial diet and on Ephestia kuehniella eggs, were compared. The diet-grown larvae showed a significantly longer developmental time and a lower adult emergence rate compared to control larvae. Moreover, the weights of the newly-emerged adults were significantly lower for adults fed during their larval stages with the artificial diet than with E. kuehniella eggs. In contrast, larval food had no effect on the duration of the pre-oviposition period or adult longevity, but the fecundity is higher for females fed as larvae with E. kuehniella. For adults fed on E. kuehniella as larvae, a significantly longer pre-oviposition period, and a lower fecundity were found for the diet-fed females compared to controls. The adult food had no significant effect on longevity and fertility. The coccinellids develop on the artificial diet but with some lower biological parameters than for E. kuehniella fed ones. Lower amino acid and fatty acid contents (in C16:0, but mainly in C16:1 and C18:3n-3) were found for the prepupae and newly-emerged females obtained from diet-reared larvae compared to controls. The analyses of the foods showed deficiencies in the artificial diet, for some amino acids but especially for fatty acids (C16:1 and C18:3n-3). These results suggest a non-optimal composition of the artificial diet and some possibilities for its improvement. A new diet supplemented with lin-seed oil (rich in unsaturated fatty acids) and offered to the larvae allows us to obtain newly emerged females richer in total amount of fatty acids than with the basic diet (62.4 instead of 17.3 µg/mg, compared to 73.4µg/mg for the E. kuehniella fed controls). These females also show higher concentrations in C16:1, and particularly C18:3n-3, as observed in the new diet itself, compared to the "first" diet. The biochemical analyses could give some characteristics allowing to evaluate the quality of the insects produced, but also bring information leading to the improvement of the diet composition and to subsequent better quality of the reared insects. Further enhancements could be intended for lipid, as well as for protein supply.