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Nutritional stress causes male-biased sex ratios in eastern spruce budworm (Lepidoptera: Tortricidae)

Published online by Cambridge University Press:  13 February 2014

Roberto Quezada-García*
Affiliation:
Centre d’Étude de la Forêt (CEF) and Département des Sciences du Bois et de la Forêt, Faculté de Foresterie, Géographie et Géomatique, Université Laval, Ville de Québec, Québec, Canada G1V 0A6
Deepa Pureswaran
Affiliation:
Natural Resources Canada, Canadian Forest Service, Ville de Québec, Québec, Canada G1V 4C7
Éric Bauce
Affiliation:
Centre d’Étude de la Forêt (CEF) and Département des Sciences du Bois et de la Forêt, Faculté de Foresterie, Géographie et Géomatique, Université Laval, Ville de Québec, Québec, Canada G1V 0A6
*
1Corresponding author (e-mail: roberto.quezada-garcia.2@ulaval.ca).

Abstract

Nutritional variability in resources may cause differential mortality between sexes resulting in biased sex ratios. If males and females differ in fitness, then mortality of the more sensitive sex can cause a bias in sex ratios, and can stimulate dispersion of males. We reared three generations of spruce budworm (Choristoneura fumiferana (Clemens); Lepidoptera: Tortricidae) on two artificial diets: a “normal” diet that provided all nutritional requirements for development and a “stress” diet (deficient in sugars and slightly higher in nitrogen), that simulated deterioration of food quality during outbreak conditions and had a detrimental impact on larval survival, development and growth. We tested the effects of continued nutritional stress on the sex ratio of pupae and adults. We found biased sex ratios in favour of males related to diet. Low quality food resulted in fewer females. This distortion was observed from the second generation onward, with a lower percentage of females reaching the pupal and adult stage. These results provide evidence that nutritional variation causes differential mortality between sexes, suggesting that females are more sensitive to nutritional stress. This is the first study that demonstrates sex ratio distortion due to nutritional selection pressure in spruce budworm. Our results indicate the importance of studying sex ratio distortion of spruce budworm in outbreak conditions.

Résumé

La variation de la qualité de la ressource alimentaire peut entraîner une mortalité différentielle entre les sexes chez la tordeuse des bourgeons de l’épinette. En effet, si la valeur sélective (fitness) des mâles et des femelles diffère, alors l'augmentation de la mortalité du sexe le plus sensible pourrait entraîner un biais dans le rapport des sexes, et il peut stimuler la dispersion des mâles. Nous avons élevé trois générations de tordeuse des bourgeons (Choristoneura fumiferana (Clemens); Lepidoptera: Tortricidae) en les nourrissant avec deux diètes artificielles: une diète équilibrée qui répond à tous les besoins nutritionnels pour soutenir un bon développement et une diète présentant un stress, soit un déficit de sucre et d'azote. Cette diète qui simulait la baisse de la qualité de la nourriture présente en conditions d'infestation a eu un impact négatif sur la survie des larves, leur développement et leur croissance. Nous avons testé les effets d'un stress nutritif continu sur le rapport des sexes de chrysalides et d'adultes. Ce type de diète favorise les mâles par rapport aux femelles. Ainsi, une faible qualité de la nourriture se traduit par une diminution du nombre de femelles. Ce déséquilibre du rapport des sexes a été observé à partir de la deuxième génération avec un pourcentage plus faible de femelles ayant atteint les stades de chrysalide et d'adulte. Ces résultats démontrent clairement que la variation de la qualité alimentaire provoque une mortalité différentielle entre les sexes, les femelles étant plus sensibles à une faible valeur nutritive des ressources alimentaires. Cette étude montre pour la première fois la présence d'un déséquilibre dans le rapport des sexes produit par un stress alimentaire chez la tordeuse des bourgeons de l’épinette. Nos résultats soulignent l'importance d’étudier le déséquilibre du rapport des sexes chez la tordeuse des bourgeons de l’épinette en conditions d’épidémie.

Type
Biodiversity & Evolution – NOTE
Copyright
Copyright © Entomological Society of Canada 2014 

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Footnotes

Subject editor: Rob Johns

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