On the mechanistic understanding of predator feeding behavior using the functional response concept

Functional Response and Intraspecific Competition of Three Ladybird Species Feeding on Aphids on Goji Berry Plants in Laboratory and Semi-Field Conditions

The aphid, Aphis gossypii Glover, is identified as a significant pest that causes severe damage to goji berries in China. To analyze the ladybird consumption of aphids, the functional responses of three ladybird species, Harmonia axyridis, Coccinella septempunctata, and Hippodamia variegata, and intraspecific competition among ladybird individuals were evaluated under laboratory conditions. Moreover, the practical impact of ladybirds on aphid population reduction was investigated in semi-field conditions. We found that all adult ladybirds of the three species exhibited a type II functional response toward aphids. According to Holling's disc equation, H. axyridis exhibited the highest searching efficiency (a = 0.79), while C. septempunctata had the shortest handling time (Th = 5.07 min) among the three ladybird species studied. Additionally, intraspecific competition had a greater impact on H. variegata (m = 0.41) compared to the other two ladybird species. The semi-field study demonstrated that H. axyridis (83.9% reduction) and C. septempunctata (78.7% reduction) exhibited higher efficacy in reducing aphid populations compared to H. variegata (27.3% reduction). This study suggests that H. axyridis and C. septempunctata exhibit potential as effective biological control agents against aphids on goji berry plants and highlights the importance of considering intraspecific competition. However, the results obtained from laboratory and semi-field studies cannot be directly extrapolated to field conditions due to the simplification of these experimental systems. Future field studies are crucial in ensuring the effective implementation of a biological control program.

Metabolic responses of predators to prey density

The metabolic cost of foraging is the dark energy of ecological systems. It is much harder to observe and to measure than its beneficial counterpart, prey consumption, yet it is not inconsequential for the dynamics of prey and predator populations. Here I define the metabolic response as the change in energy expenditure of predators in response to changes in prey density. It is analogous and intrinsically linked to the functional response, which is the change in consumption rate with prey density, as they are both shaped by adjustments in foraging activity. These adjustments are adaptive, ubiquitous in nature, and are implicitly assumed by models of predator–prey dynamics that impose consumption saturation in functional responses. By ignoring the associated metabolic responses, these models violate the principle of energy conservation and likely underestimate the strength of predator–prey interactions. Using analytical and numerical approaches, I show that missing this component of interaction has broad consequences for dynamical stability and for the robustness of ecosystems to persistent environmental or anthropogenic stressors. Negative metabolic responses – those resulting from decreases in foraging activity when more prey is available, and arguably the most common – lead to lower local stability of food webs and a faster pace of change in population sizes, including higher excitability, higher frequency of oscillations, and quicker return times to equilibrium when stable. They can also buffer the effects of press perturbations, such as harvesting, on target populations and on their prey through top-down trophic cascades, but are expected to magnify bottom-up cascades, including the effects of nutrient enrichment or the effects of altering lower trophic levels that can be caused by environmental forcing and climate change. These results have implications for any resource management approach that relies on models of food web dynamics, which is the case of many applications of ecosystem-based fisheries management. Finally, besides having their own individual effects, metabolic responses have the potential to greatly alter, or even invert, functional response-stability relationships, and therefore can be critical to an integral understanding of predation and its influence on population dynamics and persistence.

Functional response of Amblyseius eharai (Acari: Phytoseiidae) on Tetranychus urticae (Acari: Tetranychidae)

Amblyseius eharai is a generalist predatory mite that consumes spider mites, rust mites, thrips, and pollen, with a high adaptability to various plants. To better understand ecological and behavioral aspects of this species, we investigated its functional response to different stages of two-spotted spider mite, Tetranychus urticae. Furthermore, we compared its environmental adaptability with that of other referenced phytoseiids using a temperature-dependent model of the intrinsic rate of increase. We were able to calculate the functional response parameters of both sexes of A. eharai when preying on eggs or larvae of T. urticae and, for females only, when preying on the deutonymph of T. urticae. Among the various combinations tested herein, A. eharai females preying on T. urticae larvae had the highest attack rate and shortest handling time. For eggs of T. urticae, A. eharai showed a lower attack rate; however, its handling time for eggs was significantly shorter compared to other phytoseiids. Using T. urticae larva as a prey, the attack rate of female A. eharai was higher and the handling time of both sexes of this species was shorter than those of other phytoseiid mites. Amblyseius eharai populations can show maximum performance quickly due to this species’ lower optimal temperature for population growth (28.1°C) compared to other phytoseiid mites. Thus, we provided evidence that this predatory mite has the potential to be a new, effective biological control agent of greenhouse pests such as T. urticae due to its high predation capacity and low optimal temperature.