Importance of dietary nitrogen and carbohydrates to survival, growth, and reproduction in adults of the grasshopper Ageneotettix deorum (Orthoptera: Acrididae)
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Key demographic traits in insect herbivores (survival, growth, and egg production) are often responsive to variation in diet quality, especially to dietary nitrogen (N) levels. Soluble carbohydrates may also be limiting. Using defined diets under controlled laboratory conditions, we examined survival, growth, and egg production in response to a range of diet qualities in adult females of a grass-feeding grasshopper Ageneotettix deorum (Scudder). Diets varied factorially within naturally occurring ranges of total N (1–7%) and carbohydrate (4–27%) levels. N concentrations significantly impacted weight gain, egg production rate, the elapsed time until the first egg pod, and the time between the first and second egg pod. These responses were typically quadratic in nature with a maximum response near 4–5% total N. The rate of pod production rather than number of eggs per pod best explained changes in reproductive rate. Dietary carbohydrate levels seldom exerted a significant impact on demographic parameters except when interacting with N on survival, egg weight, and the period between egg pods. Clearly, factors that alter the availability of quality diet, especially total N levels, can contribute to demographic responses in A. deorum.
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