Some factors stimulating oviposition by the oophagous parasitoid Trichogramma brassicae Bezd. (Hym., Trichogrammatidae) in artificial host eggs

Abstract

The development of some Trichogramma species is possible in artificial conditions, but the number of eggs laid by females is often reduced compared to those laid in natural host eggs. Cupules made in a plastic membrane (2 μl) and filled with artificial medium containing hemolymph from Mamestra brassicae pupae were surface treated with pure solvent, Ostrinia nubilalis scale extract, or a mixture of compounds previously identified in O. nubilalis egg masses, in order to improve the oviposition performance of Trichogramma brassicae. An egg plate consisted in 54 cupules. Two day old females of T. brassicae were allowed to lay their eggs for 24 hours. Pure solvent alone stimulated the oviposition by modification of the structure of the membrane surface. O. nubilalis scale extract significantly increased the number of eggs laid (15 or 2.5 times, respectively in comparison with control or solvent). A blend of saturated hydrocarbons defined by Renou et al. (1992), stimulated the oviposition in a similar way as the extract did. If the solutions were deposited on a part of the egg plate, 77 to 88 % of the eggs were laid in the treated cupules. The extract of blend acts as contact kairomones and they will be useful to improve the oviposition of T. brassicae, permitting an increase of the adult yield in artificial conditions. Résumé Stimulation de l'oviposition de Trichogramma brassicae (Bezd.) (Hym., Trichogrammatidae) dans les œufs hôtes artificiels Le développement de certaines espèces de Trichogrammes est possible en conditions artificielles, mais souvent le nombre d'œufs déposés par les femelles est réduit par rapport à celui déposé dans des œufs hôtes naturels ou de substitution. C'est le cas avec Trichogramma brassicae Bezdenko qui est l'espèce utilisée en Europe pour la lutte biologique par lâchers inondatifs contre la pyrale du maïs Ostrinia nubilalis. Pour envisager une production de masse de ce Trichogramme en conditions artificielles il faut augmenter le rendement de l'oviposition. Renou et al. (1992) ont montré qu'un mélange d'hydrocarbures saturés augmentait l'activité de recherche des femelles de T. brassicae. Nous avons donc cherché à tester l'efficacité de ce mélange et celle d'extraits d'écailles de papillons sur le nombre d'ceœufs réellement déposés dans des cupules artificielles. Les tests sont effectués avec des plaques d'œufs hôtes artificiels composées d'une membrane, comportant des dépressions en forme de cupules (2 μl), tendue entre le couvercle et la base d'une petite boîte plastique. La surface des cupules est recouverte de la solution à tester (1 μl/cupule). Chacune des 54 cupules d'une plaque est remplie d'un milieu artificiel contenant de l'hémolymphe de Mamestra brassicae. Les femelles de T. brassicae âgées de 2 jours sont mises à pondre pendant 24 heures. Un colorant vital permet de visualiser les œufs pour le comptage. Le solvant lui‐même augmente significativement le nombre d'œufs déposés et réduit fortement le nombre de cupules sans œufs. Il semble agir en modifiant la structure de...

Aliphatic alcohols and aldehydes of the honey bee cocoon induce arrestment behavior inVarroa jacobsoni (Acari: Mesostigmata), an ectoparasite ofApis mellifera

“…25% of reacting mites on 18 µg/cm 2 of C 20 -COOH; Donzé, unreported data). It is not clear if the mixture of fatty acids synergise as observed for alkanes (Rickli et al, 1994;Grenier et al, 1993) or if the response was due to impurities in the standards. Furthermore, the high threshold needed for the arrestment response with synthetics may have originated from the bioassay conditions.…”

Kairomonal effect of acetone extracts of groundnut on foraging activities of Trichogramma chilonis (Ishii) and Chrysoperla zastrowi sillemi (Esben-Peterson)

“…These saturated long chain hydrocarbons that are present on the surface of host plants and host insects have been reported to elicit synomonal and kairomonal responses in Trichogramma spp. Grenier et al (1993).…”

“…These saturated long chain hydrocarbons that are present on the surface of host plants and host insects have been reported to elicit synomonal and kairomonal responses in Trichogramma spp. Grenier et al (1993).Similarly, plant surfaces serve many purposes, like permitting controlled release of volatiles that may deter the pests or attract natural enemies and pollinators. Higher alkanes are known to be one of the main components of cuticular waxes of plant leaves and extracts.…”

Ovipositional Synergists and Artificial Diets for Trichogramma australicum Girault (Hymenoptera: Trichogrammatidae)

“…The osmotic pressure of diet A and diet B in this study is 325 mOsm/kg and 335 mOsm/kg, respectively. This is within the range required for growth and near the pressure of diets used to rear T. dendrolimi and T. brassicae Bezdenko, the osmotic pressures for which are 320 and 340 mOsm/kg, respectively (Grenier and Bonnot 1988;Grenier et al 1993). The pH of artificial diets that we used to rear T. australicum is 6.52 and 6.61.…”

“…Low and unstable rates of oviposition into artificial eggs are two problems encountered with in vitro rearing of Trichogramma (Li 1992;Grenier et al 1993) and may be attributed to a lack of attractiveness of the artificial eggshell. Kairomones associated with the surface of natural host eggshell can stimulate interest in artificial eggshells and improve the rate of oviposition by Trichogramma (Liu et al 1995).…”