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3 4 5 Larval stage

Figure 2.14 Effects of food quality on size and number of larval instars in Spodoptera exempta (Noctuidae). Super-numerary moults are used to achieve final body size (measured as head width) in larvae feeding on two nutritionally poor grasses, Panicum and Setaria. Source: Data from Yarro (1985).

3 4 5 Larval stage

Figure 2.14 Effects of food quality on size and number of larval instars in Spodoptera exempta (Noctuidae). Super-numerary moults are used to achieve final body size (measured as head width) in larvae feeding on two nutritionally poor grasses, Panicum and Setaria. Source: Data from Yarro (1985).

development time allows the initially smaller progeny of small females to pupate at the same size as those of large females (Fox 1997). This can be considered another example of 'catch-up growth'.

Laboratory selection experiments using Drosophila have been a powerful research tool for demonstrating life history trade-offs, such as that between extended longevity and early female reproduction. In laboratory-reared D. melanogaster, increased food quality or quantity is correlated with an increase in reproduction and decrease in longevity and starvation resistance. This suggests that the tradeoff between reproduction and survival can be manipulated by diet. Simmons and Bradley (1997) used supplementary live yeast to explore the quantitative basis of this trade-off in long-lived (O) and control (B) populations of D. melanogaster. Diet enrichment caused both O and B females to produce more eggs, and both lines showed reduction in energy stores. However, the trade-off is not quantitative (Fig. 2.15): Decreasing somatic storage does not account for increasing egg production, and most of the additional energy allocated to

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