Sterol limitation in a pollen-fed omnivorous lady beetle (Coleoptera: Coccinellidae)

Nutritional constraints of non-prey foods for entomophagous arthropods are seldom investigated, yet are crucial to understanding their nutritional ecology and function within natural and managed environments. We investigated whether pollen from five maize hybrids was of variable quality for the lady beetle, Coleomegilla maculata, whether suitability of these pollens was related with their sterol profiles, and how augmenting sterols (beta-sitosterol, cholesterol, or ergosterol) affected the fitness and performance of C. maculata. Preimaginal survival, development rates, the duration of the pre-oviposition period, post-mortem adult dry weight, adult hind tibial length, sex ratio, fecundity, cohort generation time (T(c)), net replacement rate (R(0)) and intrinsic rate of increase (r) were measured. Individual sterols in the pollens were quantified using GC-MS. Pollens were of variable suitability for C. maculata; the development rate was positively correlated with the amount of 24-methylene-cholesterol and r was positively correlated with episterol and 24-methylene-lophenol found in the pollens. Performance of C. maculata was entirely unaffected by augmenting pollen meals with sterols. This research shows that pollens clearly vary in their sterol contents intraspecifically, which affects their suitability for omnivores that rely on pollen. However, sterols appear to be only one of the limiting nutrients in pollens.