How much does a drop of sugar solution benefit a hatchling of Chrysoperla pallida (Neuroptera Chrysopidae)?

Although primarily predaceous, chrysopid larvae are well known to also use honeydew, floral and extrafloral nectar, and other plant-based sugary nutrients as food. However, the extent to which the three larval stages ingest sugary liquids and the value of this sugar-feeding to subsequent survival and development (if any) have not been quantified. Here, our first experiment examines how much sugary liquid is ingested when it is offered to newly hatched or newly moulted larvae of Chrysoperla pallida. After the intake of a fructose solution, the average weight of hatchlings was almost tripled and that of freshly moulted larvae was increased by 57% (II instar) and 26% (III instar). The second experiment was designed to identify and examine the effects of larval ingestion of fructose liquid on subsequent development and survival. In this experiment, each larva was subjected to a 24-hour period of a dietary treatment three times during its development: once soon after hatching and twice again, soon after each of the two larval moults. The dietary treatments were: 1) no provision – without food or water; 2) water only; 3) fructose solution only; 4) mealworm only; 5) mealworm, with water; 6) mealworm, with fructose solution. During the periods between treatments, the larvae were fed mealworms. This experiment demonstrated that access to a sugar solution had significant positive effects on larval performance. Larvae with the fructose solution alone were significantly less likely to die than those with no provisions, water only, or, surprisingly, mealworm alone. Moreover, fastest development occurred when larvae had access to both mealworm and the fructose solution during the first 24 h of each instar. Most of the mortality occurred during the first instar, and we did not detect any effects of the treatments on the cocoon stage, neither on mortality within the cocoon nor on weight. We conclude that sugar alone does not lead to increased biomass; rather, it promotes longevity and together with a protein source, it enhances the growth rate compared to a diet of protein only. This demonstration of significant positive life-history effects from sugar intake, especially for first instars, has valuable practical application: first, for mass rearing and lab rearing methods, and second, in the context of conservation biological control.