No abstract

It is widely acknowledged that intraguild predation (IGP) occurs frequently between species of phytoseiid mites. However, in the presence of a shared resource many species of phytoseiid mites considerably reduce, or even cease, predation on each other. That being the case, IGP would then be minimal, or non-existent, and its theoretical effects on communities negligible. The aim of this work was two-fold. On the one hand, we aimed at determining the occurrence of IGP between two species of phytoseiid mites that inhabit avocado agro-ecosystems (Euseius stipulatus and E. scutalis) while considering the influence of abiotic conditions. On the other hand, we aimed at evaluating the occurrence of IGP between species of phytoseiid mites through a literature search of studies to determine whether methodologies and results in these papers supported the extended idea of IGP being widespread in the Phytoseiidae family. Our results suggested that in the presence of the shared resource predation on the IG-prey was negligible and both species seem to forage preferentially on pollen. Therefore, the interaction that most likely drives the dynamics of these two species in the field is exploitative resource competition. The literature search revealed that caution should be taken when assuming that IGP between phytoseiid mites is widespread, because only few works used experimental set ups with the adequate array of treatments allowing to assess whether IG-predators fed or not on both the IG-prey and the shared resource.

Climate change is one of the most important factors affecting the phenology, distribution, composition and diversity of organisms. In agricultural systems many pests and natural enemies are arthropods. As poikilotherm organisms, their body temperature is highly dependent on environmental conditions. Because higher trophic levels typically have lower tolerance to high temperatures than lower trophic levels, trends towards increasing local or regional temperatures may affect the strength of predator/prey interactions and disrupt pest control. Furthermore, increasing temperatures may create climate corridors that could facilitate the invasion and establishment of invasive species originating from warmer areas. In this study we examined the effect of environmental conditions on the dynamics of an agro-ecosystem community located in southern Spain, using field data on predator/prey dynamics and climate gathered during four consecutive years. The study system was composed of an ever-green tree species (avocado), an exotic tetranychid mite, and two native species of phytoseiid mites found in association with this new pest. We also present a climatological analysis of the temperature trend in the area of study during the last 28 years, as evidence of temperature warming occurring in the area. We found that the range of temperatures with positive per capita growth rates was much wider in prey than in predators, and that relative humidity contributed to explain the growth rate variation in predators, but not in prey. Predator and prey differences in thermal performance curves could explain why natural enemies did not respond numerically to the pest when environmental conditions were harsh.