1) Prof. Tamar Keasar

Climate models forecast declining rainfall in the Middle East over the next decades. Drought often reduces the abundance and diversity of plants, insect herbivores, and their natural enemies in natural habitats. However, these effects may be weaker in irrigated agroecosystems, which experience lower water stress. We asked how rainfall and land use (natural vs. agricultural) interactively affect plant-insect abundances in a tritrophic community. We sampled herbaceous plants, herbivorous insects, and parasitoid wasps in transects that extended from the center of irrigated pomegranate orchards into nearby semi-natural habitats, along Israel’s north-south rainfall gradient. Mean annual rainfall positively affected the abundance of all three trophic levels in the semi-natural habitats. The abundances of plants and herbivores increased with rainfall in the orchard margins, but not in the center of the orchards. Parasitoid abundance was unaffected by rainfall in all locations within the orchards. Focusing on the parasitoid communities, we found that climate-related variables better predicted species composition than land use. Parasitism on planthoppers and leafhoppers, endoparasitism, idiobiosis and egg parasitism were associated with mesic conditions. Parasitism on whiteflies, ectoparasitism, koinobiosis and development on larval hosts correlated positively with arid sites and seasons. We hypothesize that these life-history traits will become more common in parasitoid communities under future conditions of higher aridity. We further expect smaller effects of climate drying on tritrophic interactions in irrigated fields than in semi-natural habitats.