Abundance, interannual variation and potential pest predator role of two co‐occurring earwig species in citrus canopies

Abstract

Earwigs are usually considered pest predators in orchards. Because of its worldwide distribution, most research on earwigs focuses on the European earwig Forficula auricularia Linnaeus (Insecta: Dermaptera: Forficulidae). However, very little is known of this species in Mediterranean citrus orchards. Earwigs and aphids were collected monthly during 5 years (2006–2010) from citrus canopies. Two species of earwigs were found: F. auricularia and Forficula pubescens Gené (=Guanchia pubescens), with the latter seldom cited in the literature. The goals of this study were (i) to document the abundance of these two earwig species in Mediterranean citrus canopies; (ii) to determine whether they are positively or negatively associated with each other, or randomly distributed; (iii) to measure the interannual variation of the abundance of both species during a 5‐year period and (iv) to evaluate the potential role of earwigs as pest predators in citrus canopies. As compared to colder regions, F. auricularia active period in citrus canopies in our study site lasted longer. Both species co‐occurred randomly in canopies. In 2006, both species showed approximately the same abundance, but in 2010, F. pubescens abundance in canopies was 28 times greater than that of F. auricularia. The potential role of earwigs as pest predators is higher in the Mediterranean than in other colder regions, because of the longer active period. F. auricularia is a sedentary generalist predator, already present in citrus canopies at the onset of most pest outbreaks, while F. pubescens arrived later to the canopies, but most likely was abundant enough to contribute in the control of citrus pests.

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

“…Most published studies have been based on tree sampling, reporting the presence of F. auricularia individuals from May to October, with a May-June peak for N3 and N4 instars, and the abundance of adults in July (Lamb & Wellington, 1975;Phillips, 1981;Helsen et al, 1998;Gobin et al, 2008;Moerkens et al, 2009Moerkens et al, , 2011. Romeu-Dalmau et al (2011) also observed a longer active period in Mediterranean citrus orchards-an observation that coincides with our results. The decrease in tree shelter captures during the summer months may be explained by the increased availability of natural shelters during this period.…”

“…We found nymph instars only from April to July, thus indicating a single reproductive period per year. Similar observations were made by Romeu-Dalmau et al (2011). For both earwig species, after the peak numbers of last nymph instars (N4 or N5), we observed a population decline during molting into adults.…”

“…We can assume that when these two earwig species are found in high numbers in the shelters, no competition occurs. This may be linked to high availability of food or to the different diet preferences of For both species, the presence of males and females was similar, with a sex ratio of 1:1, coinciding with observations made by Romeu-Dalmau et al (2011) in citrus orchards.…”

“…However, Romeu-Dalmau et al (2011) observed individuals only from May to December. This finding could be attributed mainly to the sampling method, as the earlier earwig instars on the ground could not be detected by the beating technique used by those authors.…”

“…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.…”