Parasitoids physiology, development and behaviour | Boln. Asoc. esp. Ent. 21 (Supl.): 61-62 | 1997
State of art in artificial rearing of parasitoid insects, especially oophagous species
S. Grenier
ABSTRACT
Many years ago, and especially in 70´, researches were developed to try to culture entomophagous insects in artificial conditions possibly to be used in biological control strategies. At this time utilisation of natural enemies were emphasized to control agricultural pests and overeóme the side effects of Chemical pesricides.
One of the main difficulty limiting the possibility of utilization of these control agents was their mass production, especially for inundative releases. During many years, quite few researches have been conducted in this topic, but these past 5 years have revealed a sharp increase in works and positive results (Grenier, Greany and Cohén, 1994; Grenier, 1994). More and more teams all over the world are implicated in artificial rearing. Parasitoids of different orders (Díptera, Hymenoptera) including many families (Tachinidae, Braconidae, Ichneumonidae, Chalcididae, Pteromalidae, Tetrastichidae, Eupelmidae, Eulophidae, Scelionidae, Encyrtidae, Trichogrammatidae) were studied, and successfully reared in artificial media. About 40 species, including a majority of oophagous species are concemed. The best results were obíained with oophagous or pupal parasitoids which kill their host quickly and do not display a great dependence on their host physiology. On the contrary, few larval endoparasitoids (Tachinidae) have been successfully reared in vitro probably because they appeared more dependent of their host physiology.
In vitro rearing can be conducted with two main aims: Firstly, mass production and utilization of parasitoid insects in biological control strategies are the more evident aim, but secondly, artificial rearing may also constirute a tool for physiological and behavioural studies. Therefore, treatment with some chemicals should be possible (to induce insecticide resistances or behavioural learning...). Interactions between Trichogramma and some Rickettsiae of the genus Wolbachia are conducted thanks to the artificial rearing system (especially symbiot transfer attempts).
A good example of the progress achieved during these past years is shown with oophagous parasitoids. Many species of Trichogramma can be cultured in vitro from egg to adult (about 17 species), and many improvements were obtained in their cultures. The rearing system includes different technologies.
- Several systems were developed for this rearing. and at present time, the best ones are constituted by a plástic membrana with small cupules (artificial host eggs) containing artificial médium sel between the cover and the bottom of a plástic box.
- The stimulation of the oviposition is often desirable. One of the main diffículties is to obtain the egg laying in good condition. because a high number of Trichogramma eggs inside each cupule is necessaiy for a complete development. Some lepidopterous scale extracts or chemicals (hydrocarbon blend, solvents, polymers) improve significantly the oviposition of Trichogramma females.
-Two main categories of media exist : with or without insect componen!. The main insect component is hemolymph. The best results are obíained in artificial inedia containing hemolymph of Lepidoptera or holotissue extracts. Many species of Trichogramma completely develop in media containing hemolymph. But this component is sometimes diffícult to obtain and can be expensive (especially in European countries). To overeóme this problem. researches were conducted to define media without insect additives. The performances of media of different compositions (without insect additives) were compared to media with hemolymph and also with the factitious egg of Epbestia kuehniella. Biological parameters. as well as biochemical analyses, were considered. The development of T. dendrolimi was obtained in diet devoid of insect component.
- For a more convenient disposability of the media, it will be interesting to store them for a long time after lyophilization process. After long term storage, lyophilized media gave the same performances than fresh media of the same composition. Biological performances, such as percentages of parasitism. of pupation or of emergence, were similar in the different media tested (fresh or lyophilized).
In the ftiture, it will be necessary to improve the knowledge of parasitoid physiology and behaviour, to be able to propose an artificial rearing process for a higher number of parasitoid species. Some improvements are in progress for a large scale production of some species.
