Are populations of European earwigs, Forficula auricularia, density dependent?

Abstract

Biocontrol using naturally occurring predators is often limited by population parameters of those predators. Earwigs, Forficula auricularia L. (Dermaptera: Forficulidae), are important predators in fruit orchards. They are capable of suppressing outbreaks of pest species, such as pear psyllid and various apple aphid species. Earwigs therefore play an important role in integrated pest management in fruit orchards and are essential in organic top fruit cultures. However, earwig populations are very unstable, showing large between‐year variation in densities, which limits their practical use. Extensive knowledge of regulating processes of populations is therefore crucial for efficient orchard management. A 2‐year phenological study in several apple and pear orchards in Belgium showed a significant displacement of third instars during the second brood in relation to the presence of adults. We also observed a yearly population crash at the time of moulting into adults. This population decrease was correlated with earwig numbers at peak density. The crash occurred at lower earwig densities in apple orchards than in pear orchards. Six possible regulating mechanisms for this density‐dependent decrease are discussed: (1) migration, (2) pesticides or orchard management, (3) starvation, (4) pathogens, (5) parasites and parasitoids, and (6) predation or cannibalism. If we can identify these regulating processes, specific management activities could be developed to prevent the population crash, hereby increasing population densities in the orchards.

Phenology and interspecific association of Forficula auricularia and Forficula pubescens in apple orchards

“…The following year, as consequence of the hail, the trees showed more vegetative growth but less crop load, thus also reducing the number of natural shelters. Moerkens et al (2009) reported an increase in the number of adults in the shelters immediately after the harvest of pears, thereby pointing to the relevance of natural shelters. Regarding the variations observed for F. pubescens, although significant differences were observed, the variation was less than one individual per trap.…”

“…Following Lordan et al (2014a), shelters were prepared by rolling a piece of corrugated cardboard into cylinders (12 cm height × 9 cm diameter), which were protected from rain and adverse conditions by a PVC tube (15 cm height × 9.5 cm diameter). Similar shelters have been used in studies of European earwigs elsewhere (Phillips, 1981;Helsen et al, 1998;Solomon et al, 1999;Burnip et al, 2002;Gobin et al, 2006;Logan et al, 2007;He et al, 2008;Moerkens et al, 2009). Every week throughout the year, the species, number, phenological stage, and sex of adult earwigs for each shelter were recorded, and earwigs were then released at the base of the assessed tree.…”

“…In general terms, the abundance of F. auricularia among years within orchards did not change, and only in one orchard was an increase detected, while the abundance of F. pubescens decreased. Moerkens et al (2009) reported large variations in population density among orchards and years for F. auricularia.…”

“…Few studies have been devoted to the phenology of F. pubescens (Herter, 1964;Romeu-Dalmau et al, 2011). Most studies on earwigs have been conducted on F. auricularia in centralnorthern Europe (Phillips, 1981;Helsen et al, 1998;Kocarek, 1998;Gobin et al, 2008;Moerkens et al, 2009), New Zealand (Burnip et al, 2002;Suckling et al, 2006), and North America (Fulton, 1924;Crumb et al, 1941;Lamb, 1975Lamb, , 1976Lamb & Wellington, 1975); however, little is known about these insects in Mediterranean apple orchards, where they may also act as key predators in pip fruit and citrus orchards but as pests in stone fruit orchards and vineyards.…”

Use of Predators for the Biological control of Eriosoma lanigerum (wooly apple aphids) on apple

“…Because of this, there will not be enough earwigs in the place, where they are previously attacking aphids. Thus, this low population of earwigs will not be able to control WAA population once threshold of aphid population is crossed (Moerkens et al, 2009;Quarrell et al, 2017).…”