Diversity of insects associated with olive (Oleaceae) groves across a dryland climate gradient in Algeria

Abstract

AbstractThis study investigated insect diversity of olive (Olea europaea Linnaeus (Oleaceae)) groves grown in arid and semiarid climates in northeastern Algeria. Using several sampling techniques, a total of 1326 insect specimens were collected and identified into 151 species, 124 genera, 65 families, and 10 orders. Hymenoptera and Coleoptera were quantitatively the most abundant, whereas the dominant functional feeding groups were phytophages then predators. The entomofauna included several olive pests such as Bactrocera oleae (Rossi) (Diptera: Tephritidae), Parlatoria oleae (Colvée) (Hemiptera: Diaspididae), Euphyllura olivina (Costa) (Hemiptera: Liviidae), and Liothrips oleae Costa (Thysanoptera: Phlaeothripidae). Although insect diversity parameters recorded for both observed and expected species richness were higher in olive groves grown under semiarid compared with arid climate, the completeness rate of species richness obtained using the nonparametric incidence estimators was higher in arid olive groves. Generalised linear models showed that the number of individuals and species richness varied significantly between climates (P < 0.01), whereas the variation of the rest of diversity parameters was not significant. Diversity traits of insect assemblage of each climatic region were positively correlated. Besides, the Mantel permutation test revealed similar patterns (r = 0.91, P < 0.0001) between correlation matrices of the two climates. When increasing the number of samples, species richness extrapolation revealed that diversity is expected to increase by 130% in olive groves grown under arid climate and 93% in semiarid climate. These increases are related to continuous appearance of rare and scarce insects as demonstrated by species rarefaction curves. Even with high evenness values of insect communities, similarity was low between climate indicating the rarity and scarcity of populations.