Capacités de discrimination des femelles de quatre souches de Callosobruchus maculatus Fab. (Coléoptera : Chrysomelidae, Bruchinae) pour la localisation de l’hôte et la ponte aux dépens d’hôtes secondaires

L’objectif de cette étude est de savoir comment les femelles de quatre souches de Callosobruchus maculatus F., localisent leur hôte, distribuent les oeufs sur des graines de taille différente dans des conditions de libre choix, de semi choix et de non choix. Ainsi, des couples de C. maculatus ont été transférés du niébé, Vigna unguiculata (L.) Walp. (Fabaceae), et maintenus sur les graines de deux variétés de voandzou, Vigna subterranea (L.) Verdc. (Fabaceae), et du pois d’angole, Cajanus cajan (L.) Millsp (Fabaceae), trois ans durant. La capacité des femelles à reconnaître les odeurs de ces quatre types de graines a été testée à l’aide d’un olfactomètre et dans un dispositif tridimensionnel. Elles ont été ensuite mises en contact avec les différentes graines pour la ponte. Dans l’olfatomètre, lorsqu’elles ont le choix entre l’air pur et l’air provenant de leurs hôtes d’origine, elles sont significativement attirées par l’air odorant. Quand les femelles issues des souches du voandzou ou du pois d’angole ont le choix entre le niébé et leur plante d’origine, elles préfèrent le niébé. Dans le dispositif tridimensionnel, quand les femelles issues du voandzou ou du pois d’angole ont un libre choix entre les quatre types de graines, elles (> 30%) préfèrent leurs plantes hôtes d’origine. Les odeurs dégagées par les graines semblent contribuer à l’orientation des femelles vers ces graines. C. maculatus utilisent des signaux chimiques dans la localisation de leurs hôtes. Ceci entraînerait ou stimulerait l’utilisation des répulsifs et attractants dans la gestion intégrée des insectes de stocks.Mots clés: Capacités de discrimination, localisation, ponte, C. maculatus, plantes hôtes secondaire

Effects of Volatiles from Maruca vitrata Larvae and Caterpillar-Infested Flowers of Their Host Plant Vigna unguiculata on the Foraging Behavior of the Parasitoid Apanteles taragamae

The parasitoid wasp Apanteles taragamae is a promising candidate for the biological control of the legume pod borer Maruca vitrata, which recently has been introduced into Benin. The effects of volatiles from cowpea and peabush flowers and Maruca vitrata larvae on host selection behavior of the parasitoid Apanteles taragamae were investigated under laboratory conditions by using a Y-tube olfactometer. Naïve and oviposition-experienced female wasps were given a choice between several odor sources that included (1) uninfested, (2) Maruca vitrata-infested, and (3) mechanically damaged cowpea flowers, as well as (4) stem portions of peabush plants carrying leaves and flowers, (5) healthy M. vitrata larvae, and moribund (6), and live (7) virus-infected M. vitrata larvae. Responses of naïve and oviposition-experienced female wasps did not differ for any of the odor source combinations. Wasps were significantly attracted to floral volatiles produced by cowpea flowers that had been infested with M. vitrata larvae and from which the larvae had been removed. Apanteles taragamae females also were attracted to Maruca vitrata-infested flowers after removal of both the larvae and their feces. Female wasps discriminated between volatiles from previously infested flowers and mechanically damaged flowers. Uninfested cowpea flowers attracted only oviposition-experienced wasps that had received a rewarding experience (i.e. the parasitization of two M. vitrata larvae feeding on cowpea flowers) before the olfactometer test. Wasps also were attracted to uninfested leaves and flowers of peabush. Moreover, they were also attracted to healthy and live virus-infected M. vitrata larvae, but not when the latter were moribund. Our data show that, similarly to what has been extensively been reported for foliar volatiles, flowers of plants also emit parasitoid-attracting volatiles in response to being infested with an herbivore

Can the understory affect the Hymenoptera parasitoids in a Eucalyptus plantation?

The understory in forest plantations can increase richness and diversity of natural enemies due to greater plant species richness. The objective of this study was to test the hypothesis that the presence of the understory and climatic season in the region (wet or dry) can increase the richness and abundance of Hymenoptera parasitoids in Eucalyptus plantations, in the municipality of Belo Oriente, Minas Gerais State, Brazil. In each eucalyptus cultivation (five areas of cultivation) ten Malaise traps were installed, five with the understory and five without it. A total of 9,639 individuals from 30 families of the Hymenoptera parasitoids were collected, with Mymaridae, Scelionidae, Encyrtidae and Braconidae being the most collected ones with 4,934, 1,212, 619 and 612 individuals, respectively. The eucalyptus stands with and without the understory showed percentage of individuals 45.65% and 54.35% collected, respectively. The understory did not represent a positive effect on the overall abundance of the individuals Hymenoptera in the E. grandis stands, but rather exerted a positive effect on the specific families of the parasitoids of this order

Playing the hare or the tortoise in parasitoids: could different oviposition strategies have an influence in host partitioning in two Aphidius species?

In this paper, we compare the host selection behaviours of two parasitoids, Aphidius rhopalosiphi and Aphidius picipes, in order to analyse whether behavioural adaptations to the defensive behaviour of their host (the grain aphid Sitobion avenae) could, in part, be responsible for the simultaneous presence of both species in cereal fields. The oviposition behaviour of A. picipes differed from that of A. rhopalosiphi by,including a number of 'fluttering wings' sequences followed by immobility It resulted in a 44 times longer host-handling time for A. picipes than for A. rhopalosiphi. Hosts attacked by A. picipes exhibited fewer defensive behaviours than hosts attacked by A. rhopalosiphi.. A. picipes and A. rhopalosiphi rejected respectively 0% and 53% of unparasitized hosts presenting cornicle secretions, one of the defensive means of aphids. Furthermore, A. picipes females rejected 100% of the hosts that were already parasitized, whereas A. rhopalosiphi was previously described to reject only 20 to 40% of such hosts. Such differences could be explained by the way the two species deal with the aphid defensive behaviour. Field analyses, showed that A. rhopalosiphi was already present in wheat fields in early April whereas A. picipes appeared later and only achieved a low level of parasitism. However, when both species were present simultaneously, they shared the same resource

Early adult learning affects host preferences in the tephritid parasitoid Psyttalia concolor (Hymenoptera: Braconidae)

Parasitic wasps rely on a hierarchy of stimuli to locate their hosts. Olfactory cues from the natal host complex affect parasitoid preferences and can be learned by parasitoids during larval stages and the early adult stage. While the existence of pre-imaginal conditioning has been documented in several braconid aphid parasitoids, no evidence has yet been provided for parasitic wasps attacking Tephritidae. Psyttalia concolor (Hymenoptera: Braconidae) is a koinobiont larval–pupal endoparasitoid of tephritid flies. In this study, we evaluated the influence of larval and early adult experience on subsequent host seeking in P. concolor females. Parasitoids were reared using Ceratitis capitata or Bactrocera oleae larvae as hosts, and emerging wasp adults were tested for host preferences in two-choice bioassays. P. concolor females preferred to oviposit in, and had higher oviposition success rates on the natal host. When P. concolor females were excised from their host puparia, preventing them from chewing emergence holes, they lost their natal host preference, solidifying the evidence of early adult learning for host selection. This study adds to the growing body of basic knowledge on braconid host-location behavior. From an applied point of view, training procedures for early adult learning has potential for use in mass rearing of parasitoids employed in biological control programs against tephritid flies