Bad housekeeping: why do aphids leave their exuviae inside the colony?

<p>Abstract</p> <p>Background</p> <p>Animals can gain protection against predators and parasites by living in groups. The encounter-dilution effect provides protection when the probability of detection of a group does not increase in proportion to group size (i.e. encounter effect), so that predators do not offset the encounter effect by attacking more members of the group (i.e. dilution effect). In this paper, we propose a novel mechanism by which prey insects could gain by producing decoys that act as multiple targets for predators or parasitoids if these decoys are recognised as preys or hosts and negatively affect the patch foraging strategy of these predators and parasitoids. Such a decoy mechanism could be present in aphid colonies in which aphid exuviae are recognised and attacked by Aphidiine wasps.</p> <p>Results</p> <p>We conducted a behavioural study to evaluate the effect of exuviae on parasitoid patch residence time and egg allocation in experimental aphid patches with or without exuviae. We showed that exuviae are recognised and attacked at the same level as aphids when both are present in the patch. While parasitism rate was not significantly lower in patches with exuviae when the parasitoid left the patch, the time wasted by parasitoids to handle exuviae did influence the patch residence time. As a consequence, the attack rate on the live aphids was lower in patches that contain exuviae.</p> <p>Conclusion</p> <p>Aphids had more time available to flee and thus each individual might gain protection against parasitoids by leaving their exuviae near and within the colony. These results demonstrate that the encounter-dilution effect provided by living in a group can be enhanced by extra-materials that act as decoy for natural enemies.</p

Efficiency of Three Diets for Larval Development in Mass Rearing Aedes albopictus (Diptera: Culicidae)

A fundamental step in establishing a mass production system is the development of a larval diet that promotes high adult performance at a reasonable cost. To identify a suitable larval diet for Aedes albopictus (Skuse), three diets were compared: a standard laboratory diet used at the Centro Agricoltura Ambiente, Italy (CAA) and two diets developed specifically for mosquito mass rearing at the FAO/IAEA Laboratory, Austria. The two IAEA diets, without affecting survival to the pupal stage, resulted in a shorter time to pupation and to emergence when compared with the CAA diet. At 24 h from pupation onset, 50 and 90% of the male pupae produced on the CAA and IAEA diets, respectively, had formed and could be collected. The diet received during the larval stage affected the longevity of adult males with access to water only, with best results observed when using the CAA larval diet. However, similar longevity among diet treatments was observed when males were supplied with sucrose solution. No differences were observed in the effects of larval diet on adult male size or female fecundity and fertility. Considering these results, along with the relative costs of the three diets, the IAEA 2 diet is found to be the preferred choice for mass rearing of Aedes albopictus, particularly if a sugar meal can be given to adult males before release, to ensure their teneral reserves are sufficient for survival, dispersal, and mating in the field

Aedes albopictus Adult Medium Mass Rearing for SIT Program Development

For the production of several hundred thousands of Aedes albopictus sterile males for the implementation of a Sterile Insect Technique (SIT) program, no costly mass-rearing equipment is needed during the initial phases, as optimized rearing at laboratory scale can be sufficient for the first steps. The aim of this study was to maximize the egg production by optimizing adult rearing methods for Ae. albopictus. The effect of parameters such as male/female ratio, density of adults, membrane type for blood feeding, quantity of blood delivered, continuous or discontinuous blood feeding, and surface of substrates for egg laying on overall egg production was tested to find optimized conditions. Based on the number of eggs produced per cage in response to the parameters tested, the optimum cage set-up was seen to be 1500 adults in a 30 &times; 30 &times; 30 cm cage with a male/female sex ratio of 1:3, fed by fresh bovine blood for periods of 30 min using a cellulose membrane covering a 10 cm stainless steel plate heated by a Hemotek device, and the provision of five oviposition cups to collect eggs. With this set-up, production per cage can reach a maximum of 35,000 eggs per week

Caractérisation du stock de spermatozoïdes et stratégies de reproduction chez deux hyménoptères parasitoïdes de bruches

Chez Eupelmus orientalis et Dinarmus basalis, deux espèces d'hyménoptères parasitoïdes, nous avons caractérisé la qualité des spermatozoïdes présents dans les organes de stockage des mâles et des femelles au cours des différentes étapes de la vie reproductive et dans différentes conditions d'accouplements. Cette qualité est mesurée grâce à l'utilisation de 2 fluorochromes : IP, caractérisant les cellules non-viables et SYBR-14, les viables. Les durées de vie des mâles Dinarmus basalis et Eupelmus orientalis sont respectivement de 66 et 12 jours. Chez Eupelmus orientalis, la qualité des spermatozoïdes stockés dans les vésicules séminales n'est pas altérée, chez Dinarmus basalis, elle est maintenue jusqu'à 30 jours. Les durées de vie des femelles Dinarmus basalis et Eupelmus orientalis sont respectivement de 115 et 50 jours. Lorsque les femelles Eupelmus orientalis sont mises en ponte, la qualité des spermatozoïdes n'est pas altérée, à l'inverse lorsqu'elles sont laissées en rétention de ponte pendant 21 jours, une baisse significative de cette qualité apparaît. Chez Dinarmus basalis, une rétention de ponte durant 115 jours ne modifie pas la qualité des spermatozoïdes. Chez les deux espèces, quelque soit le nombre d'accouplements, la qualité des spermatozoïdes transférés par le mâle aux femelles est constante ; de même, chez les femelles, celle-ci n'est pas modifiée avec le nombre d'accouplements. Grâce à l'utilisation de ce test prédictif, une mesure fiable du succès reproducteur des mâles et des femelles des deux espèces est possible dès le début de vie des adultes. La qualité des spermatozoïdes et leur gestion sont des éléments déterminant des stratégies de reproduction de ces insectes.TOURS-BU Sciences Pharmacie (372612104) / SudocSudocFranceF

Why do sperm-depleted parasitoid males continue to mate?

Insect males of several parasitoid species have limited amount of sperm at emergence and experience sperm depletion when mate acquisition rate is high, suggesting that sperm production and storage could be a limiting factor for male's fitness. Sperm-depleted males of the parasitoid wasp Trichogramma evanescens continue to mate, and the impact of this behavior on sperm storage by females has been studied. Virgin females T. evanescens stored 50.6 � 13.1 (Mean � SD) sperm when mating first with a virgin male. However, when these females mated first with a sperm-depleted male and then with a virgin male, they stored only 18.9 � 7.8 sperm, indicating that mating with a sperm-depleted male has a cost and limits sperm acquisition from fertile males. Following a mating with a sperm-depleted male, females had to mate with three virgin males to restore their sperm supply confirming that additional mating enabled the female to store a limited number of sperm. According to our results, by continuing to mate, sperm-depleted males do not prevent mates from copulating again but they decrease their ability to store other male's sperm. Continuing to mate could be a strategy to increase the relative fitness of sperm-depleted males. Copyright 2006.Hymenoptera; polyandry; reproduction; reproductive strategy