Influence of the number of hosts and the risk of predation on the foraging behavior of the parasitoid Eretmocerus eremicus

BACKGROUND

Parasitoids are natural enemies that can modify their behaviors as they search for hosts based on the characteristics of the sites in which they forage. Theoretical models predict that a parasitoid will stay for longer periods in high-quality sites or patches than in those of low quality. In turn, patch quality may be linked to factors such as the number of hosts and the risk of predation. In the present study, we sought to determine if the factors of the number of hosts, risk of predation, and their interaction influence the foraging behavior of the parasitoid Eretmocerus eremicus (Hymenoptera: Aphelinidae) as theory predicts. To do this, we evaluated different parameters of parasitoid foraging behavior, such as residence time, number of oviposition events, and attacks, in sites of different patch quality.

RESULTS

Our results show that when the factors, number of hosts, and, risk of predation, were evaluated separately, E. eremicus resided for longer periods and oviposited more frequently in patches with a high number of hosts and low risk of predation than in other patches. However, when both of these factors were combined, only the number of hosts influenced some aspects of the foraging behavior of this parasitoid, such as the number of oviposition events and attacks.

CONCLUSION

For some parasitoids like E. eremicus, theoretical predictions may be fulfilled when patch quality is linked to the number of hosts but will not be fully satisfied when patch quality is related to the risk of predation. Furthermore, at sites with different combinations of host numbers and risk of predation, host number appears to be more critical than predation risk. These results suggest that the performance of the parasitoid E. eremicus to control whiteflies will be mainly mediated by the levels of whitefly infestation and, to a small extent, by the risk of predation to which the parasitoid is subjected. © 2023 Society of Chemical Industry.

The Importance of Forest Simplification and Litter Disturbance in Defining the Assembly of Ground-Foraging Ants

Currently, we are facing many ecosystem changes derived from years of anthropogenic disturbances. Habitat simplification stands out among human-derived impacts, due to its detrimental effects on vegetation structure and associated biota. Here, we assessed the effects of litter disturbance and forest simplification on a tropical ground-foraging ant community. To do that, we tested whether ant richness will be negatively affected by litter disturbance and habitat simplification. Additionally, we tested whether litter disturbance affects the time of resource discovery and dominance, and if so, whether its effects are intensified by forest simplification. This study occurred at Rio Doce State Park, a preserved area of Atlantic Forest in Southeastern Brazil. We experimentally simulated litter disturbance by removing the leaf litter and superficial soil layer in a mahogany monoculture forest and preserved Atlantic Forest. We sampled ants using paired-mixed baits of protein and carbohydrate in 12 points, half of them in each forest type. As expected, we found higher richness in the preserved and non-disturbed forest. Moreover, resource discovery was faster in disturbed monoculture, but bait dominance was higher in the undisturbed preserved forest. Litter heterogeneity seems to play an important role in determining ant dispersion and intra-specific communication, as we observed that litter disturbance impacts were strengthened by forest simplification. Our results highlight the efficiency of ground-foraging ants as bioindicators of disturbance and habitat quality. Moreover, our study indicates how distinct types of disturbances can act synergistically, changing the assembly of associated biota.

State-dependent foraging by caribou with different nutritional requirements

Foraging by animals is hypothesized to be state-dependent, that is, varying with physiological condition of individuals. State often is defined by energy reserves, but state also can reflect differences in nutritional requirements (e.g., for reproduction, lactation, growth, etc.). Testing hypotheses about state-dependent foraging in ungulates is difficult because fine-scale data needed to evaluate these hypotheses generally are lacking. To evaluate whether foraging by caribou (Rangifer tarandus) was state-dependent, we compared bite and intake rates, travel rates, dietary quality, forage selection, daily foraging time, and foraging strategies of caribou with three levels of nutritional requirements (lactating adults, nonlactating adults, subadults 1–2 years old). Only daily foraging times and daily nutrient intakes differed among nutritional classes of caribou. Lactating caribou foraged longer per day than nonlactating caribou—a difference that was greatest at the highest rates of intake, but which persisted even when intake was below requirements. Further, at sites where caribou achieved high rates of intake, caribou in each nutritional class continued foraging even after satisfying daily nutritional requirements, which was consistent with a foraging strategy to maximize energy intake. Foraging time by caribou was partially state-dependent, highlighting the importance of accounting for physiological state in studies of animal behavior. Fine-scale foraging behaviors may influence larger-scale behavioral strategies, with potential implications for conservation and management.