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

Efficient gene targeting mediated by a lentiviral vector-associated meganuclease

Gene targeting can be achieved with lentiviral vectors delivering donor sequences along with a nuclease that creates a locus-specific double-strand break (DSB). Therapeutic applications of this system would require an appropriate control of the amount of endonuclease delivered to the target cells, and potentially toxic sustained expression must be avoided. Here, we show that the nuclease can be transferred into cells as a protein associated with a lentiviral vector particle. I-SceI, a prototypic meganuclease from yeast, was incorporated into the virions as a fusion with Vpr, an HIV accessory protein. Integration-deficient lentiviral vectors containing the donor sequences and the I-SceI fusion protein were tested in reporter cells in which targeting events were scored by the repair of a puromycin resistance gene. Molecular analysis of the targeted locus indicated a 2-fold higher frequency of the expected recombination event when the nuclease was delivered as a protein rather than encoded by a separate vector. In both systems, a proportion of clones displayed multiple integrated copies of the donor sequences, either as tandems at the targeted locus or at unrelated loci. These integration patterns were dependent upon the mode of meganuclease delivery, suggesting distinct recombination processes

Epicuticular Factors Involved In Host Recognition For The Aphid Parasitoid Aphidius Rhopalosiphi

In insect parasitoids, fitness is dependent on the host finding and recognition abilities of the female. Host recognition cues have been described for various host-parasitoid systems, but are still under investigation in aphid parasitoids. Our study aimed to clarify the respective role of physical and chemical cues in recognition of the aphid cuticle. Shed aphid exuviae were used as an elicitor in order to avoid any influence of color, movement, or volatiles present in a living aphid. We assessed the effect of chemical and heat treatments on the texture of the cuticle by using scanning electron microscopy and tested the recognition of treated cuticles by the parasitoid. We showed that recognition cues of the cuticle can be removed chemically (using combined treatments with n-hexane and methanol). Moreover, heat treatment destroyed the physical texture of the cuticle without significantly reducing parasitoid recognition. In a second step, we showed that epicuticular extracts deposited on pieces of paper triggered female attack behavior. First results concerning the chemical composition of the active extract are presented. This study shows that chemical compounds extractable by organic solvents mediate cuticle recognition by aphid parasitoids

Ecological traits of a new aphid parasitoid, \u3ci\u3eEndaphis fugitiva\u3c/i\u3e (Diptera: Cecidomyiidae), and its potential for biological control of the banana aphid, \u3ci\u3ePentalonia nigronervosa\u3c/i\u3e (Hemiptera: Aphididae)

Most parasitoids of aphids are small wasps belonging to the families Braconidae or Aphelinidae. However, some dipteran parasitoids are also known to use aphids as hosts. We describe and give life-history information on a new species of aphid parasitoid, Endaphis fugitiva Gagné and Muratori, found to parasitize the banana aphid, Pentalonia nigronervosa Coquerel, the vector of banana bunchy top virus. Field and laboratory observations show that fly eggs are laid on the leaves near an aphid colony, the newly hatched fly larvae search for hosts while crawling on the leaf, and then penetrate the aphid between the legs and thorax. They develop as koinobiont endoparasitoids, and eventually emerge from the aphid anus and fall to the ground to pupate in the soil. We provide data relevant to parasitoid rearing on patterns of emergence, adult longevity, and effects of pupation substrate on adult emergence rate, and we discuss the potential of this new species to contribute to the biocontrol of banana aphid in Hawaii

The impact of patch encounter rate on patch residence time of female parasitoids increases with patch quality

1. For animal species that forage on patchily distributed resources, patch time allocation is of prime importance to their reproductive success. According to Charnov's marginal value theorem (MVT), the rate of patch encounter should influence negatively the patch residence time: as the rate of patch encounter decreases, the patch residence time increases. Moreover, the MVT predicts that animals should stay longer in high quality patches. 2. Using the aphid parasitoid Aphidius rhopalosiphi (Hymenoptera: Aphidiinae), the effects of these two factors (patch encounter rate and host density) were combined in order to test if the increment in patch residence time for a given decrease in patch encounter rate was larger for high quality patches than for low quality patches. 3. The results show a significant effect of the interaction between the two factors. In high host density patches, parasitoids spent more time if they experienced a low patch encounter rate, while in low host density patches, patch encounter rate had no significant effect on the patch residence time. This suggests that the response of A. rhopalosiphi females to patch encounter rate varied with host density in the patch. Moreover, the same interaction effect was observed for the number of ovipositor contacts on aphids. 4. Parasitoid females can use patch encounter rate to estimate patch density in the habitat but the effect of this estimate on their patch residence time is modulated by patch quality. Staying longer in a patch when patches are rare is more advantageous when the fitness gained by doing so is large. In low quality patches, the expected fitness gain is small and the female may gain more by leaving and taking her chance at finding another patch

Cold-induced expression of diapause in Praon volucre: fitness cost and morpho-physiological characterization

Cold exposure (2 degrees C for 7 days) in constant darkness at mummy stage induces diapause expression in 9% of the Praon volucre Haliday population. Diapausing parasitoids show a significant delay in emergence time compared with nondiapausing counterparts. A diapause-mediated polyphenism is observed in mummy colour, with diapausing mummies being clearly darker than nondiapausing ones. The diapause status of dark mummies is confirmed by a significant reduction in metabolic rate. Diapausing parasitoids also display specific morphological characteristics: they are heavier (fresh and dry mass) and accumulate larger fat reserves than nondiapausing counterparts. The diapause status is associated with a fitness cost in terms of adult longevity. There is no evidence of diapause-related change in supercooling ability

Clonal variation in aggregation and defensive behavior in pea aphids

The presence of several clonal lineages within a single aphid colony raises the possibility for conflict between clones over safer positions within multiclonal colonies. To study the effect of relatedness on group dynamics, we manipulated the clonal composition of pea aphid groups (2 pure clonal groups and 1 mixed group) under laboratory conditions and allowed the individuals to cluster together freely on a leaf. We found variation between the clones in both the speed at which individuals joined the group and the aggregation level, where mixed colonies showed intermediates. Experimental and simulation results showed a nonrandom distribution of aphids in mixed colonies between the center and the periphery area, suggesting that one of the clones exhibits selfish herd behavior. In a second set of experiments, aphid groups were exposed to a single parasitoid female. Interestingly, we found that aphids from pure colonies were more likely to react by falling from the plant than individuals in mixed colonies. Our results revealed unexpected kin recognition abilities by nonsocial aphids, which make aphid colony dynamics more complex than previously thought. © 2014 The Author