Danielle Rojas-Rousse

Interspecific competition between Eupelmus vuilleti and Dinarmus basalis, two solitary ectoparasitoids of Bruchidae larvae and pupae

Coexistence of two solitary ectoparasitoids of bruchids may be the result of counter‐balanced competition. Some strategies in interspecific competition at the extrinsic level of female behaviour are identified. Dinarmus basalis (Rondani) (Hymenoptera; Pteromalidae) has adapted an evasion strategy to avoid competition. Females of D. basalis show interspecific discrimination against hosts parasitized by Eupelmus vuilleti Crawford (Hymenoptera; Eupelmidae) and lay fewer eggs in the presence of females or hosts parasitized by the latter. Eupelmus vuilleti has adapted an aggressive strategy. In contrast to D. basalis, E. vuilleti concentrates her ovipositions on hosts already parasitized by D. basalis. Females of E. vuilleti preferably use oviposition holes made by other parasitoids, and are able to kill eggs and larvae of D. basalis selectively by thrusts of their ovipositor (ovicide and larvicide). Furthermore, E. vuilleti can act as a facultative hyperparasitoid on older larvae of D. basalis. The number of E. vuilleti offspring is not affected by the presence of D. basalis on a host. Our study does not provide insight in the process of larval competition.

Organogenèse et ultrastructure des sensilles placoïdes des antennes de Diadromus pulchellus wesmael (Hymenoptera : Ichneumonidae)

Abstract The placoid sensilla (PS) of the antenna of D. pulchellus (Hymenoptera : Ichneumonidae) are interpreted as composed of 2 superposed cuticular chambers. Organogenesis of a PS during imaginal moulting reveals the existence of 30–40 neurons accompanied by glial cells (a periaxonal and a peridendritic), and 5 enveloping cells, which secrete the epicuticle of the sensillum. These cells are distributed in a trichogen type (2 cells), a tormogen type (2 cells), and an odd cell enveloping the whole. In the differentiated sensillum, the distal dendritic processes are branched and elongated into the upper chamber. The 4 internal enveloping cells form microvilli that remain in the lower chamber; the external enveloping cell has vesicular cytoplasm, and it separates the internal cells from the cuticle.

Hyperparasitisme facultatif de parasitoïdes en cours de développement par les femelles des ectoparasitoïdes Eupelmus vuilleti et Eupelmus orientalis Craw

Abstract In a community of three ectoparasitoids, Dinarmus basalis, Eupelmus vuilleti and E. orientalis, the host Callosobruchus maculatus parasitised 48 h before by D. basalis, is accepted by E. vuilleti females after they have eliminated the eggs and neonatal larvae of D. basalis. This ovicidal and larvicidal behaviour enables E. vuilleti to develop on C. maculatus instead of D. basalis. E. vuilleti females are able to parasitise the L5 larval stage and the pupa of D. basalis: their larvae therefore feed at the expense of the developing parasitoid. This trophic level is that of hyperparasitism. However, E. vuilleti females rarely practise hyperparasitism on their own L5 larvae and on those of E. orientalis. This behaviour reveals a high behavioural plasticity enabled by intra- and interspecific recognition of parasitoids used as hosts. Hyperparasitism activity in E. orientalis females is higher than that in E. vuilleti females since they hyperparasitise host parasitoids more frequently without preferential species choice. However, E. vuilleti seems to be free from competitive pressure with E. orientalis, as the former penetrates deeply into a grain store contaminated with C. maculatus in contrast to E. orientalis females, which remain on the surface from where they escaped.

Description et fonctionnement de l'appareil genital interne de Diadromus pulchellus wesmeal (Hymenoptera: Ichneumonidae)—I: Testicules, canaux deferents, glandes annexes, canaux collecteurs, canal ejaculateur du male

Abstract In Diadromus pulchellus , the long vas deferens ends at the base of the large accessory gland. The distal part of the vas deferens, incorporated in the glands muscular shell, opens up near the insertion of the ejaculatory duct. The secretions collected in the gland cavity are rich in acid mucopolysaccharids and proteins and are discharged into the ejaculatory duct at copulation. The movement of the spermatozoa, stored along the vas deferens, is very fast. They come into contact with the glandular secretions during passage towards the ejaculatory duct.

L'activité reproductrice et le développement de Bruchidius atrolineatus (Pic) sur les gousses sèches de Vigna unguiculata (Walp) en zone sahélienne, mise en évidence d'une diapause imaginale

Résumé—Bruchidius atrolineatus apparait dans la nature à la fin de la saison des pluies lorsque les gousses de sa plante hôte Vigna unguiculata commencent à mûrir. Les oeufs sont déposés le long de la suture ventrale à l’emplacement des graines. Quand les oeufs ne sont pas parasités par un hyménoptère Trichogrammatidae, leurs larves pénètrent dans les graines et la mortalité est faible au cours du développement post-embryonnaire. La plupart des adultes émergeant des gousses mûres ont des organes reproducteurs fonctionnels. Les femelles de cette génération repondent sur les mêmes gousses et leurs larves se développent dans les graines durant la première partie de la saison sèche, caractérisée par une température diurne élevée et une humidité relative faible. Si les premiers adultes issus de cette seconde ponte ont des organes reproducteurs fonctionnels, les suivants (60% de la population) sont en diapause reproductrice. De tels insectes diapausants ont également été retrouvés dans des abris à proximité des zones de culture de Vigna unguiculata. Les conditions d’induction et de levée de cette diapause n’ont pas encore été étudiées. Cette diapause reproductrice permet probablement le maintien dans le nature des populations de Bruchidius atrolineatus pendant la saison sèche lorsque la plante hôte est absente.Abstract—Bruchidius atrolineatus appears at the end of the rainy season when pods of its host plant Vigna unguiculata begin to mature. The eggs are deposited along the ventral suture of pods in the vicinity of the seeds. When the eggs are not attacked by Trichogrammatidae their larvae penetrate the seeds and mortality is low during the post-embryonic development. Most of the adults emerging at pod maturity have functional reproductive organs. In-that case the females laid on the same mature pods and larvae develop inside the seeds during the first part of the drying season characterised by high diurnal temperature and low relative humity. If the first emerged adults have functional reproductive organs, the following (60% of the population) are in reproductive diapause. Such diapausing insects have been found during the dry season in shelters near the cultivated fields of Vigna unguiculata. Induction or termination of this reproductive diapause are not yet studied. This diapause probably allows the maintenance of populations during the dry season in absence of host plant.

Structure et fonctionnement de la spermatheque chez l'endoparasite solitaire Diadromus pulchellus wesmael (Hymenoptera : Ichneumonidae)

Abstract Studies of the fine anatomy and ultrastructure of the spermathecae of endoparasitic females of Diadromus pulchellus Wesmael (Hymenoptera : Ichneumonidae) were made in order to understand the role of this organ in sex-ratio regulation. The spermatheca, approximately 50 μm in diameter, includes a spherical capsule and a relatively voluminous gland, each connected by a duct to the spermathecal duct that opens into the vagina. The spermatheca is enveloped by a complex muscular system. Circular muscle fibres surround the capsule and the canal. The capsule wall is made up of thick cuticle resting upon well-developed epithelial cells, containing numerous vesticles derived from the endoplasmic reticulum. The gland has the typical structure of epidermal glands but lamella-shaped lipid secretions are present. Lastly, the vaginal wall includes a zone of differentiated cells surrounding the opening of the spermathecal canal. Emphasis is placed on the role of the muscular system and the importance of glandular secretions.

Energy losses as a function of temperature during the development of Diadromus collaris and D. pulchellus, solitary endoparasites of Acrolepiopsis assectella (Lepidoptera: Plutellidae)

Abstract Using gravimetric and calorimetric measurements, we have studied the action of thermal environmental variations (from a 15–25°C thermoperiod to 20–30°C) on the total energy spent during the endoparasitic development of Diadromus pulchellus and D. collaris (Hymenoptera: Ichneumonidae) in the pupae of Acrolepiopsis assectella Z. (Hymenoptera: Plutellidae) to maintain their basal metabolism, activity and thermoregulation. These two Diadromus species expended an identical 24 h maintenance energy in the 15–25°C thermoperiod ( 0.24 cal 24 h for females and 0.26 cal 24 h for males). Maintenance energy in the 20–30°C thermoperiod was identical in males ( 0.38 cal 24 h ) and somewhat different in females (0.35 and 0.37 cal 24 h respectively). A 5°C temperature increase (15 to 20°C and 25 to 30°C) during the dark and light periods resulted in increased 24 h energy expenditures by both species, somewhat greater in D. pulchellus females.

Frequency and viability of diploid and haploid male offspring of mated females of solitary endoparasitoid Diadromus pulchellus

Sex determination in the order Hymenoptera is based on arrhenotoky, hymenopteran males are usually haploid and females diploid. Males of the Ichneumonidae Diadromus pulchellus, solitary endoparasitoid of A Acrolepiopsis assectella pupae, are normally haploid, but diploid males are present in a natural population and can be obtained in an experimental population. The future of an ovocyte laid by mated females of the solitary endoparasitoid D. pulchellus was characterised by six probabilities related to the sex and development of the ovocyte. The probabilities of fertilisation of female ovocyte (k1) or non-fertilisation (k3) showed that an inseminated female functioned as a unmated female for half of the time (since k1 = 0.492 and k3 = 0.455) with the probability of fertilisation of male ovocyte, k2, equal to 0.053. The survival probabilities of each type of ovocyte showed that an ovocyte had a high probability of developing up to the adult stage, although the difference between the calculated sex ratios at laying (males/females = 1.032) and at emergence (0.90) revealed a slight reduction in the number of haploid sons. The probabilities of fertilisation and of viability of all the ovocytes laid by each of the 33 mated females were analysed by an ascending hierarchical classification of Euclidean distances and by an analysis of their principal components. The 33 mothers were distributed into four distinct sub-groups characterised by a sex ratio varying from an exclusive presence of females to an exclusive presence of males. Our hypothesis was that this distribution in four sub-sets could not simply result from the random nature of the sample.