2 results
Previous herbivory alerts conspecific gravid sawflies to avoid unsuitable host plants
- G. A. Valladares, M. V. Coll-Aráoz, M. Alderete, M. T. Vera, P. C. Fernández
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- Journal:
- Bulletin of Entomological Research / Volume 110 / Issue 4 / August 2020
- Published online by Cambridge University Press:
- 09 December 2019, pp. 438-448
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The willow sawfly, Nematus oligospilus (Förster), is a pest in Salix commercial forests and has been reported worldwide. Female adults must recognize a suitable host plant to oviposit, since her offspring lack the ability to move to another host. We evaluated the effect of conspecific herbivory on the oviposition choices of N. oligospilus females by providing damaged (DP) and undamaged (UP) plants of Salix humboldtiana, a native willow from South America, as oviposition substrates. Local and systemic effects were studied. For the local treatment, a twig from the DP with damaged leaves was contrasted to a twig from a UP in dual choice experiments. For systemic treatment, a twig from the DP with intact leaves was contrasted to a twig from a UP. We estimated the use of olfactory and contact cues by comparing volatile emission of DP and UP, and by analysing the behaviour of the females during host recognition after landing on the leaf surface. In the context of the preference–performance hypothesis (PPH), we also tested if oviposition site selection maximizes offspring fitness by evaluating neonate hatching, larval performance and survival of larvae that were born and bred on either DP or UP. Our results demonstrate that previous conspecific herbivory on S. humboldtiana has a dramatic impact on female oviposition choices and offspring performance of the sawfly N. oligospilus. Females showed a marked preference for laying eggs on UP of S. humboldtiana. This preference was found for both local and systemic treatments. Volatile emission was quantitatively changed after conspecific damage suggesting that it could be related to N. oligospilus avoidance. In the dual choice preference experiments, the analysis of the behaviour of the females once landing on the leaf surface suggested the use of contact cues triggering egg laying on leaves from UP and avoidance of leaves from DP. Furthermore, 48 h of previous conspecific feeding was sufficient to dramatically impair neonate hatching, as well as larval development and survival, suggesting a rapid and effective reaction of the induced resistance mechanisms of the tree. In agreement with the PPH, these results support the idea that decisions made by colonizing females may result in optimal outcomes for their offspring in a barely studied insect model, and also opens the opportunity for studying tree-induced defences in the unexplored South American willow S. humboldtiana.
Novel microsatellite DNA markers indicate strict parthenogenesis and few genotypes in the invasive willow sawfly Nematus oligospilus
- V. Caron, M. Norgate, F.J. Ede, T. Nyman, P. Sunnucks
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- Journal:
- Bulletin of Entomological Research / Volume 103 / Issue 1 / February 2013
- Published online by Cambridge University Press:
- 29 August 2012, pp. 74-88
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Invasive organisms can have major impacts on the environment. Some invasive organisms are parthenogenetic in their invasive range and, therefore, exist as a number of asexual lineages (=clones). Determining the reproductive mode of invasive species has important implications for understanding the evolutionary genetics of such species, more especially, for management-relevant traits. The willow sawfly Nematus oligospilus Förster (Hymenoptera: Tenthredinidae) has been introduced unintentionally into several countries in the Southern Hemisphere where it has subsequently become invasive. To assess the population expansion, reproductive mode and host-plant relationships of this insect, microsatellite markers were developed and applied to natural populations sampled from the native and expanded range, along with sequencing of the cytochrome-oxidase I mitochondrial DNA (mtDNA) region. Other tenthredinids across a spectrum of taxonomic similarity to N. oligospilus and having a range of life strategies were also tested. Strict parthenogenesis was apparent within invasive N. oligospilus populations throughout the Southern Hemisphere, which comprised only a small number of genotypes. Sequences of mtDNA were identical for all individuals tested in the invasive range. The microsatellite markers were used successfully in several sawfly species, especially Nematus spp. and other genera of the Nematini tribe, with the degree of success inversely related to genetic divergence as estimated from COI sequences. The confirmation of parthenogenetic reproduction in N. oligospilus and the fact that it has a very limited pool of genotypes have important implications for understanding and managing this species and its biology, including in terms of phenotypic diversity, host relationships, implications for spread and future adaptive change. It would appear to be an excellent model study system for understanding evolution of invasive parthenogens that diverge without sexual reproduction and genetic recombination.