Multicomponent sex pheromone inMacrocentrus grandii Goidanich (Hymenoptera: Braconidae)

A multicomponent sex pheromone inMacrocentms grandii Goidanich (Hymenoptera: Braconidae) was demonstrated using wind-tunnel and field bioassays. In wind-tunnel bioassays, three Florisii fractions from female wasps (hexane, 5%, and 50% ether in hexane) and one from male wasps (50% ether in hexane) were attractive to males. The hexane and 5% ether in hexane fractions each elicited similar male behavioral responses. These included upwind anemotaxis, casting, landing on the source, wing fanning, and mating attempts between males. The 50% ether in hexane fraction, whether male- or female-derived, initiated a strong flight response by males but few landings on the source. In addition, the 50% ether in hexane fraction was found to synergize strongly the hexane fraction. All females tested in the wind tunnel gave no responses to male- or female-derived extracts. Field tests generally supported the wind-tunnel results, although no field attraction was observed for the 5% ether in hexane fraction.

Placenta-like structure of the aphid endoparasitic wasp Aphidius ervi: a strategy of optimal resources acquisition

Aphidius ervi (Hymenoptera: Braconidae) is an entomophagous parasitoid known to be an effective parasitoid of several aphid species of economic importance. A reduction of its production cost during mass rearing for inundative release is needed to improve its use in biological control of pests. In these contexts, a careful analysis of its entire development phases within its host is needed. This paper shows that this parasitoid has some characteristics in its embryological development rather complex and different from most other reported insects, which can be phylogenetically very close. First, its yolkless egg allows a high fecundity of the female but force them to hatch from the egg shell rapidly to the host hemocoel. An early cellularisation allowing a rapid differentiation of a serosa membrane seems to confirm this hypothesis. The serosa wraps the developing embryo until the first instar larva stage and invades the host tissues by microvilli projections and form a placenta like structure able to divert host resources and allowing nutrition and respiration of embryo. Such interspecific invasion, at the cellular level, recalls mammal's trophoblasts that anchors maternal uterine wall and underlines the high adaptation of A. ervi to develop in the host body.

Biochemical crypsis in the avoidance of natural enemies by an insect herbivore

Plant-herbivore interactions provide well studied examples of coevolution, but little is known about how such interactions are influenced by the third trophic level. Here we show that larvae of the specialized lepidopteran herbivore Heliothis subflexa reduce their vulnerability to natural enemies through adaptation to a remarkable and previously unknown feature of their host plant, Physalis angulata: The fruits of this plant lack linolenic acid (LA), which is required for the development of most insects. By overcoming this nutritional deficiency, H. subflexa larvae achieve numerous advantages. First, they gain near-exclusive access to a food resource: we demonstrate that closely related Heliothis virescens larvae cannot develop on P. angulata fruit unless the fruit are treated with LA. Second, they reduce their vulnerability to enemies: LA is a key component of volicitin, an elicitor of plant-volatile-signaling defenses. We demonstrate that volicitin is absent in the oral secretions of fruit-feeding caterpillars, that the volatile profiles of plants induced by fruit feeding differ from those induced by leaf feeding or by feeding on LA-treated fruit, and that the former are far less attractive to female Cardiochiles nigriceps parasitoids. Finally, they render themselves nutritionally unsuitable as hosts for enemies that require LA for their own development: we show that C. nigriceps larvae fail to develop within the bodies of fruit-feeding caterpillars but do develop in caterpillars feeding on LA-treated fruit. Thus, H. subflexa larvae not only overcome a serious dietary deficiency but also reduce their vulnerability to natural enemies through a form of "biochemical crypsis."

Growth-promoting effects of ecdysteroids and juvenile hormone on in vitro development of the larval endoparasitoid, Venturia canescens (Hymenoptera: Ichneumonidae)

We previously reported that lipophorin, fetal bovine serum (FBS), and 20-hydroxyecdysone (20-HE) are essential for the development of the larval endoparasitoid Venturia canescens larvae in vitro. The present study was undertaken to determine the optimal concentrations of those three substances in the MGM-450 medium, and to examine the hormonal effects of ecdysteroids and juvenile hormone (JH) on the development of the parasitoid larvae in vitro. When the culture was started with embryos at the post-germband stage, concentrations of 3 mg/ml of lipophorin and 20% of FBS were most suitable for the development of the parasitoid. The growth-promoting effect of 20-HE increased in a concentration-dependent manner and peaked at a concentration of 1 &mgr;g/ml. Excess concentration led to malformations of the larvae. Three other ecdysteroids, ecdysone, 2-deoxy-20-hydroxyecdysone, and polypodine B had the same effect, although their activity was lower than that of 20-HE. Cholesterol had no effect; most larvae failed to develop. When the medium was supplemented with JH, the duration of the developmental period was significantly shortened, but this hormone was not found to be essential.

Nutrition and culture of entomophagous insects

This article reviews the current state of knowledge concerning the nutrition of entomophagous insects and other arthropods. Early nutritional investigations focused principally on the basic dietary and nutritional requirements for beneficial insects. Based on these findings, the first attempts were made to develop mass culture methods and to formulate artificial diets that would allow rearing of parasitoids and predators in the absence of host or prey, as well as the latter's food sources. Although limited success was achieved, these studies established the nutritional foundation for later advances. Recently, attention has focused on the interaction between nutrition, physiology, behavior, and ecology of the different life stages of entomophagous species within a unified concept of nutritional ecology. This approach has resulted in more comprehensive understanding of nutrition, which in turn has facilitated the continuous artificial culture of several parasites and predators. Additional studies have confirmed the importance of supplemental feeding of the adult stages of beneficial insects for maximizing reproduction and longevity. Applications of nutritional ecology to biological control are discussed.

The in vitro development from egg to prepupa of Campoletis sonorensis (Hymenoptera: Ichneumonidae) in an artificial medium: importance of physical factors

A further attempt to improve the in vitro rearing of the solitary larval endoparasitoid Campoletis sonorensis (Hymenoptera: Ichneumonidae) was made after third instars were obtained in previous studies. Respiration was an important factor for the parasitoid's continued development: both small diet volumes that exposed the larval cuticle to air and O(2)greatly improved growth and development of C. sonorensis. Fifth instars were obtained when the parasitoid larvae were reared in medium volumes of 0.25ml and 0.1ml per well. Increasing the O(2) tension of the air resulted in larger larvae and prepupae. The agar layer under the nutritional medium was designed to slowly remove water from the diet. The results indicated that a drier environment was important for the parasitoid at the terminal stage. One percent and 0.8% agar gels, which removed water from the diet more rapidly, provided a drier environment and resulted in improved larval growth compared to the 0.6% agar gel. The detrimental effect of higher concentration of chicken egg yolk mixed in the diet was eliminated by using a dry egg yolk layer covered by an agar layer. This sandwich technique resulted in more parasitoid larvae molting to the final larval instar (5th) and the formation of many prepupae. However, the development of prepupae was premature and none of the fifth instar larvae successfully formed a normal cocoon.