Nitrogen fertiliser affects the functional response and prey consumption ofHarmonia axyridis(Coleoptera: Coccinellidae) feeding on cereal aphids

Predator–prey interactions are influenced by nitrogen availability. Wheat (Triticum aestivumcv. Solstice) plants were provided with four levels of nitrogen and examined the responses of coccinellid predator,Harmonia axyridisto cereal aphids,Rhopalosiphum padiandSitobion avenae. Increased nitrogen application improved nitrogen contents of the plants and also the body weight of cereal aphids feeding on them. In no‐choice feeding trials,H. axyridisconsumed more aphids on low fertilised plants, suggesting a compensatory consumption to overcome reduced biomass (lower aphid size). Total biomass devoured byH. axyridison all nitrogen fertiliser treatments was not statistically different. Logistic regression analysis of the proportion of prey consumed demonstrated that all developmental stages (larval and adult) ofH. axyridisexhibited the type II functional response on all nitrogen fertiliser treatments. The rate of successful search (a′) of third and fourth instars and adults were the same across all fertiliser treatments suggesting that nitrogen fertilisation did not affecta′. Maximum handling time for the first instars ofH. axyridisonR. padi(3.81 h−1) andS. avenae(4.59 h−1) was on the highest nitrogen treatment while minimum handling time was for the adults ofH. axyridisonR. padi(0.20 h−1) andS. avenae(0.20 h−1) on the lowest nitrogen treatment. Handling time varied at varying fertiliser treatments within all instars and affected the predator's efficiency. The functional response curve, rate of successful search and handling time provide the information needed to understand the predator–prey interaction betweenH. axyridisand these cereals aphids. This could lead to the development of a better strategy for the biological control ofR. padiandS. avenaeat any particular level of nitrogen fertiliser regime in the field crops.