Mixoplankton interferences in dilution grazing experiments

It remains unclear as to how mixoplankton (coupled phototrophy and phagotrophy in one cell) affects the estimation of grazing rates obtained from the widely used dilution grazing technique. To address this issue, we prepared laboratory-controlled dilution experiments with known mixtures of phyto-, protozoo-, and mixoplankton, operated under different light regimes and species combinations. Our results evidenced that chlorophyll is an inadequate proxy for phytoplankton when mixoplankton are present. Conversely, species-specific cellular counts could assist (although not fully solve) in the integration of mixoplanktonic activity in a dilution experiment. Moreover, cell counts can expose prey selectivity patterns and intraguild interactions among grazers. Our results also demonstrated that whole community approaches mimic reality better than single-species laboratory experiments. We also confirmed that light is required for protozoo- and mixoplankton to correctly express their feeding activity, and that overall diurnal grazing is higher than nocturnal. Thus, we recommend that a detailed examination of initial and final plankton communities should become routine in dilution experiments, and that incubations should preferably be started at the beginning of both day and night periods. Finally, we hypothesize that in silico approaches may help disentangle the contribution of mixoplankton to the community grazing of a given system.

Intraguild Interactions between the Mealybug Predators Cryptolaemus montrouzieri and Chrysoperla carnea

The ladybird Cryptolaemus montrouzieri and the green lacewing Chrysoperla carnea have shown potential for use in augmentative biological control of mealybug pests in greenhouse crops. In the context of combining these predators within an integrated pest management system, the risk of negative intraguild interactions between both predators was evaluated in a laboratory setting. Different life stages of either predator were confronted in petri dish arenas containing a Ficus benjamina leaf, and after 24 h the incidence and direction of intraguild predation (IGP) was recorded for each combination. The effect of adding Planococcus citri nymphs or Ephestia kuehniella eggs as extraguild prey on the level of IGP was also studied. IGP was frequently observed between the two predator species and was asymmetrical in favour of C. carnea in most cases. The presence of extraguild prey reduced the number of IGP events between the predators to a similar extent. The relevance of the observed intraguild interactions for the combined use of these predators in protected cultivation is discussed.

Mathematical Analysis of Intraguild Interactions among Hosts, Parasitoids and Predators

In this work, we consider a mathematical model of an omnivorous ecosystem in which intermediate predators are infected by parasites. We first establish the boundeness and positivity of solution with conditions. Then the existence and local stability of all equilibria are clarified in R4. Finally, some global dynamics will be analyzed.

Agonistic interactions and island biogeography as drivers of carnivore spatial and temporal activity at multiple scales

Carnivore communities can be diverse and complex, and lack of knowledge regarding intraguild interactions and alternative drivers of carnivore distributions can preclude effective conservation of co-occurring species. As such, our objectives were to evaluate the relative importance of intraguild interactions and island biogeography to carnivore community spatiotemporal activity at multiple spatial scales. We monitored the carnivore community of the Apostle Islands National Lakeshore (Wisconsin, United States) using a grid of camera traps from 2014-2018. We used generalized linear mixed-effects models and information-theoretic model selection to evaluate whether subordinate carnivore presence was related to dominant carnivore relative abundance (interactions) or to island biogeography at the island-level and camera site-level, and we calculated temporal overlap between each pair of species to determine whether subordinate carnivores were using temporal segregation. At the island-level, the relative importance of interactions and island biogeography was species dependent. At the site-level, relative abundance of dominant carnivores was not a significant predictor of subordinate carnivore presence, and all pairs exhibited high or neutral temporal overlap. At the island-level, island biogeography and interactions may both impact species distributions; however, at finer spatial scales, the carnivore community may be using alternative segregation strategies, or the island system may preclude segregation.

Super-predation and intraguild interactions in a multi-predator-one-prey system alter the abundance and behaviour of green peach aphid (Hemiptera: Aphididae)

The dynamics of interactions amongst natural enemies are central to the investigation of insect pest ecology. Ternary and quaternary interactions between parasitoids and predators in the presence of entomophagous organisms are yet to be comprehensively explored. We investigated the performance of a clone of green peach aphid (Myzus persicae (Sulzer); Hemiptera: Aphididae), raised on savoy cabbage (Brassica oleracea Linnaeus; Brassicaceae), under all possible combinations of: I) the parasitoid Aphidius colemani Viereck (Hymenoptera: Braconidae); II) the predator Chrysoperla carnea (Stephens) (Neuroptera: Chrysopidae); III) the predator Adalia bipunctata (Linnaeus) (Coleoptera: Coccinellidae); and IV) the spider Parasteatoda tepidariorum (Koch) (Araneae: Theridiidae). We demonstrate a considerably differential green peach aphid abundance, polyphenism, and fine-scale spatial distribution in response to the combination, number, and identity of the present enemy species and their interactions. Surprisingly, certain combinations led to thriving green peach aphid populations due to interference between enemies; whereas, other combinations resulted in tangible collective suppression of the population. At the frontier of agroecology and entomology, we provide fresh insights on the effects of conflict and synergy between natural enemies sharing a pest of a cash crop as prey, highlighting the consequences of the presence of a novel synanthropic spider, as a top predator, on pest regulation.