Phenology, coexistence and potential role as pest predators of Forficula auricularia and Forficula pubescens (Dermaptera: Forficulidae) in Mediterranean organic citrus trees

Background/Question/Methods

As omnivorous insects, earwigs are considered key pest predators but they are also occasionally considered pests in agroecosystems. Due to the worldwide distribution of Forficula auricularia L., most published research about earwigs focus on this species. Along with other predators and parasitoids, F.auricularia has been proved to effectively regulate several pest populations in apple and pear trees and vineyards. However, very little is known of the European earwig neither in the Mediterranean region nor in citrus trees. Earwigs and aphids were collected monthly during five years (2006-2010) from citrus canopies using beating trays. Two species of earwigs were found: Forficula auricularia and Forficula pubescens Serville. While the former has been well studied in many aspects, the latter is hardly cited in the literature. The aims of this study were (a) to study the phenology of these two co-occurring species of earwigs in citrus canopies; (b) to examine if the presence of these two species in trees was independent or not; (c) to establish the temporal evolution of their abundance during a five year period, and (d) to evaluate their potential role as pest predators in citrus orchards.

Results/Conclusions

The European earwig in Mediterranean organic citrus trees has two reproduction periods per year; the first period occurs earlier and the second later than what is described in the literature. F. pubescens has only one reproduction period in spring. The presence of these species in citrus trees was independent. In 2006 both species had approximately the same abundance, but during the five years of the study F. pubescens exponentially increased its relative abundance and in 2010 its abundance in canopies relative to that of F. auricularia was 28 times higher. European earwig abundance was negatively related to aphid abundance, suggesting a top-down regulation of aphids by this earwig. By contrast, F. pubescens abundance did not show a significant relationship with aphid abundance. This difference in both species abundance in relation to that of aphids might be explained by the early arrival of F. auricularia in trees (in April) and the later arrival of F. pubescens (in May), when aphid attack was already high. Finally, the observed phenology of the two species of earwigs suggested that they are potential predators of several common citrus pests including aphids, leafminers, woolly whiteflies, and scale insects.