Figure 1. How the intake of protein and carbohydrate influence longevity and lifetime egg production in adults of three insect species.

Individuals were given ad libitum access to one of 28 (Drosophila and the Queensland fruit fly, Q-fly) or 24 (field cricket) diets varying in the ratio and total concentration of protein to carbohydrate (P:C). Plotted onto arrays of points of nutrient intake are fitted surfaces for the two performance variable, which rise in elevation from dark blue to dark red. Unbroken red lines indicate the dietary P:C that maximized the response variable, whereas the dotted lines indicate isocaloric intakes. In each case, insects lived longest when the diet contained a low P:C, and lifespan declined as P:C rose. Female reproductive output was maximal on higher P:C diets than sustained greatest longevity, but fell as P:C rose further, even at high total energy intakes. Data are replotted from Lee et al. [3] (Drosophila), Maklakov et al. [11] (field crickets), and Fanson et al. [4] (Q-fly).