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Effects of early growth conditions on body composition, allometry, and survival in the ladybird beetle Harmonia axyridis

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Abstract:

During both the larval and adult stages, the ladybird beetles Harmonia axyridis (Pallas, 1773) feed primarily on aphids, populations of which may fluctuate dramatically in time and space. Harmonia axyridis were reared under three resource treatments: high, low, and improving. We predicted that beetles experiencing consistently poor larval conditions would allocate limited resources to dispersal traits (by increasing relative wing surface area and fat storage), whereas larvae facing good or improving conditions were predicted to allocate preferentially to reproductive traits. As predicted, beetles reared at low food had lower wing loading and stored more fat than individuals reared at consistently high food. When conditions were initially poor but improved during development, body size was reduced relative to the high food treatment, though wing area scaled similarly. Allocation of fat and protein was dependent on both sex and treatment. Females in improving conditions stored less fat, and males less protein, relative to low food conditions. This is suggestive of a trade-off between reproduction and dispersal that is resolved differently between the sexes. Unexpectedly, adult survival under starvation was not appreciably affected by larval growth conditions, although males lived about 10 days longer, on average.

Durant à la fois leurs stades larvaires et adultes, les coccinelles Harmonia axyridis (Pallas, 1773) se nourrissent principalement de pucerons dont les populations peuvent fluctuer de façon spectaculaire dans le temps et l’espace. Nous avons élevé des H. axyridis dans trois conditions expérimentales de ressources, favorables, médiocres et en amélioration. Nous avions prédit que les coléoptères qui connaissent des conditions larvaires médiocres devraient allouer leurs ressources limitées aux traits reliés à la dispersion (augmentation de la surface relative des ailes et accumulation de lipides), alors que les larves en conditions favorables ou en amélioration devraient les allouer de préférence aux traits reliés à la reproduction. Comme prédit, les coléoptères élevés dans des conditions alimentaires médiocres ont une charge alaire réduite et accumulent plus de lipides que les individus gardés continuellement en conditions alimentaires favorables. Lorsque les conditions sont médiocres au début et s’améliorent au cours du développement, la taille du corps est réduite par rapport à ce qui s’observe dans les conditions alimentaires favorables, bien que la surface alaire se développe de la même façon. L’allocation des lipides et des protéines dépend à la fois du sexe et des conditions expérimentales. Par rapport aux individus en conditions alimentaires médiocres, les femelles en conditions en amélioration stockent moins de lipides et les mâles moins de protéines. Cela semble indiquer un compromis entre la reproduction et la dispersion qui est résolu différemment par les deux sexes. De façon inattendue, la survie des adultes dans les conditions de pénurie alimentaire n’est pas affectée de manière appréciable par les conditions de croissance des larves, bien que les mâles vivent en moyenne environ dix jours de plus.

Document Type: Research Article

Publication date: 2009-02-01

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  • Published since 1929, this monthly journal reports on primary research contributed by respected international scientists in the broad field of zoology, including behaviour, biochemistry and physiology, developmental biology, ecology, genetics, morphology and ultrastructure, parasitology and pathology, and systematics and evolution. It also invites experts to submit review articles on topics of current interest.
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