Earwigs, Forficula auricularia, are key generalist predators to a variety of orchard pests.

However, numbers of earwigs have declined in both organic and IPM orchards in recent

years. Both Integrated and Organic fruit growers have tried to re-establish earwig

populations, thus far with little success. To understand earwig population dynamics and to

find measures to increase natural orchard populations, we conducted a detailed

phenological survey of earwigs in orchards. Earwigs were sampled while sheltering during

daytime in artificial refuges. They move into the trees from the third nymph stage onwards.

In most orchards, a small second brood is produced in summer, and this has a positive

impact on population size in fall. We see only minor differences in phenology between

apple and pear orchards, mainly caused by differences in alternative hiding places.

Earwigs show an inexplicable reduction in numbers at the timing of moulting into adults.

When earwig phenology is correlated with pest phenology in apple and pear, its use for

pest control of major pests is clear

Gobin, B.

Leirs, H.

Moerkens, R.

Peusens, G.

English

Organic Eprints

208Understanding earwig phenology in top fruit orchards B. Gobin1, G. Peusens1, R. Moerkens2 and H. Leirs2AbstractEarwigs, Forficula auricularia, are key generalist predators to a variety of orchard pests. However, numbers of earwigs have declined in both organic and IPM orchards in recent years.  Both  Integrated  and  Organic  fruit  growers  have  tried  to  re-establish  earwig populations, thus far with little success. To understand earwig population dynamics and to find  measures  to  increase  natural  orchard  populations,  we  conducted  a  detailed phenological survey of earwigs in orchards. Earwigs were sampled while sheltering during daytime in artificial refuges. They move into the trees from the third nymph stage onwards. In most orchards, a small second brood is produced in summer, and this has a positive impact on population size in fall. We see only minor differences in phenology between apple  and  pear  orchards,  mainly  caused  by  differences  in  alternative  hiding  places. Earwigs show an inexplicable reduction in numbers at the timing of moulting into adults. When earwig phenology is correlated with pest phenology in apple and pear, its use for pest control of major pests is clear. Keywords: Forficula auricularia, biological control, population dynamics, apple, pearIntroductionThe common earwig, Forficula auricularia, is a generalist feeder that survives on plant material, mosses or fungi, but, given the chance, preferentially consumes small arthropods (Phillips 1981). A number of lab studies focussing on specific orchard pests demonstrated earwig pest consumption ability of scale insects (Karsemeijer, 1973; McLeod & Chant, 1952), aphids, (Buxton & Madge, 1976; Noppert et al., 1987; Phillips, 1981), spider mites (Phillips 1981), and Psyllids (Lenfant, et al. 1994; Phillips, 1981). Only for four of these orchard pests, some studies attempted to demonstrate efficacy in more practically relevant semi-field or field trials. The best documented predatory effect of earwigs is that toward the woolly apple aphid Eriosoma lanigerum, a major pest in apple orchards with integrated or organic pest management. Both a study in Holland (Mueller et al. 1988) and in Australia (Nicholas et al. 2005) demonstrated a direct effect of earwig exclusion on woolly apple aphid proliferation, and a negative correlation between degree of aphid infestation and the number of earwigs present on the trees. Also in the highly abundant pear pest Cacopsyllapyri, a semifield test showed consumption of large numbers of eggs by earwigs confined to sleeves on pear branches (Lenfant et al., 1994).  Field control of three more pest species was  not  clearly  demonstrated:  the  same  research  team  found  contradictory  results  in controlling the green apple aphid Aphis pomi (Carroll & Hoyt, 1984; Carroll et al., 1985), while a small scale field study on the apple-grass aphid Rhopalosiphum insertum and the spider mite Panonychus ulmi could not demonstrate any effect of earwig presence (Phillips 1981).Earwigs are univoltine. Males and females form pairs in fall and hibernate in underground nests. Once the female lays eggs in late winter or early spring, she expels the males and provides broodcare to eggs and the first nymph stage.                                                 1 Zoology Department, pcfruit (formerly Gorsem Research Station), Fruittuinweg 1, B-3800 Sint-Truiden, Belgium 2 Evolutionary Biology Group, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium Archived at http://orgprints.org/13678/209Females  abandon  the  nests  when  nymphs  become  second  instars,  these  nymphs  will disperse shortly thereafter and move to weeds, shrubs or trees. Especially around early summer (end of june, early july) abundance of late instar earwigs is present in orchard trees.  Although the general life cycle of earwigs is well understood, most quantitative studies on earwig presence in orchards are limited to summer occurrence only, as earwigs are most abundant in July. To understand what limits the presence of earwigs in orchards, we  conducted  a  detailed  survey  of  earwig  presence  covering  the  whole  season.  To manage a univoltine species such as F. auricularia a good knowledge of its life history is required. The species was recently identified with molecular techniques as a complex of at least  two  sibling  species,  named  species  A  and  B  (sensu  Wirth  et  al.,  1998).  These species have distinct life history strategies, having either a single or two broods, and likely a slightly different timing of onset of egg-laying in winter.  Material and Methods As  earwigs  are  nocturnal,  they  readily  hide  in  artificial  refuges  during  the  daytime. Providing two shelters in each of 10-20 trees per orchard allowed assessment of earwig numbers. Shelters consisted of corrugated cardboard rolls inserted in a Styrofoam coffee cup for rain protection and attached horizontally to a strong branch with iron wire. For earwig counts, cardboard rolls were opened and all earwigs collected in a tray. Nymphal stages were differentiated by size and antennal segments; male and female adults based on sexual dimorphism in cerci. Once counted, earwigs were released on the assessed tree and the shelter was returned to the same location within the tree. Earwigs were counted at least  once  a  week,  starting  upon  appearance  in  the  trees  (start  of  June)  until  adults migrate to the soil (end of October). Sampled orchards were a mix of IPM and organic orchards.0510152025303540456-612-619-626-64-710-717-725-731-77-814-822-829-84-913-920-93-1017-1030-10apple adultspear adultsapple L4pear L4apple L3pear L3Figure 1: Average numbers of 3rd and 4th instar nymphs and adults in apple and pear orchards in BelgiumArchived at http://orgprints.org/13678/210Results and discussion Earwig larvae appear in the fruit trees from the end of May onwards. We observed very few L2 nymphs in the cardboard shelters (an average maximum of 1.57 in apple and 0.5 in pear, early june). From the third nymphal stage upwards, earwigs gradually became more abundant  in  the  trees  (Figure  1).  The  discrepancy  between  the  peak  of  3rd  and  4th nymphal  stages  suggests  that  younger  nymphs  still  dwell  on  the  ground.  Addition  of shelters on the soil  indeed enhanced the capture of 3rd instar nymphs.Earwig numbers were greatest at the 4th nymphal stage. In both apple and pear orchards, a  sharp  decline  in  numbers  was  observed  at  the  timing  of  moulting  of  L4  into  adults, around mid July. We are currently testing several hypothesis as to what might cause this effect. In most orchards, earwigs produce a second brood, with a rather limited numerical contribution  to  the  earwig  population.  In  apple,  the  adult  population  observed  in  the shelters remains at a rather constant level, with a small increase when a second brood is present. In contrast, we observe a progressive decline of the adult population in pear in August, with a considerable increase in fall, after harvest. The pattern in pear is likely due to a sampling artefact, i.e. the reduced necessity for earwigs to use artificial shelters when pear clusters grow, offering numerous alternative hiding places. Once these hiding places are  removed  at  harvest,  the  population  again  moves  into  the  artificial  refuges.  The presence of a second brood has a positive effect on the population size in fall, a few orchards lacking a second brood show a gradual decline towards fall. The latter orchards clearly  have  a  single  species  (the  one  with  the  single  brood),  but  it  is  as  yet  unclear whether the other orchards have a mixture of both subspecies or solely the “two-brood” subspecies.  To  estimate  the  predation  potential  of  earwigs  on  the  main  orchard  pests,  we  roughly correlated  earwig  phenology  with  pest  phenology  as  was  observed  at  the  Gorsem research station for the past 50 years (Table 1). The phenology of earwigs is ideal to help control summer and fall generations of E. lanigerum in apple and C. pyri in pear. Exclusion experiments in apple orchards indeed showed that these pests increase when earwigs are absent (Mueller et al., 1988; Nicholas 2005). Earwigs are also likely to assist in controlling summer generations of leafrollers and various Lepidopteran pests. The potential earwig impact on codling moth (C. Pomonella) will be minor, as only eggs and recently hatched larvae  are  exposed.  Once  the  codling  moth  larvae  penetrated  the  fruit  skin,  it  is  well protected from earwig predation within the fruit, and be only at risk again in a late stage when the bore hole is large. Earwigs come to late in the trees to control most aphids, but might in some years assist in cleaning up colony remnants in June. This explains the variability in earwig control of green apple aphids described from successive field trials (Carroll & Hoyt, 1984; Carroll et al., 1985). Even when earwigs can consume red spider mite  eggs  (Phillips  1981),  we  believe  the  impact  of  earwigs  on  that  pest  to  be  minor compared to its control with predatory mites, the most proliferate beneficial in the majority of belgian apple orchards.In sum, though earwigs will play a role in control of a variety of pest insects, their main contribution to biological control in top fruit will be against woolly aphid in apple and Psyllain  pear.  As  Psyllid  adults  are  highly  mobile,  earwig  control  will  be  restricted  within  a season. In contrast, earwig control of the fall population of Eriosoma will likely contribute to a reduction in numbers at the onset of the next season.  Archived at http://orgprints.org/13678/211Table 1: The control potential of F. auricularia for major top fruit pests in Belgium, estimated by linking earwig and pest phenologies.  Main Top Fruit Pest speciesPresence of damaging stagePotential Forficula control Adoxophyes orana  1st generation: April  no  Earwigs still underground 2nd generation: August  yes  Presence of adult earwigs, low numbers of nymphsDysaphis plantaginea  March to May  no  Earwigs still underground Cydia pomonella  May to August  weak  Presence coincides but likely only eggs and recently hatched larvae can be reached by earwigs Eriosoma lanigerum  Resume activity: March  no  Earwigs still underground, unknown whether they feed on root colonies   Main migration: Mid May  no  Earwigs come too late to prevent migration   Summer population  yes  Earwigs assist Aphelinus in controlling Eriosomaby mid July and throughout August   Fall population  yes  Earwigs are main natural enemy at this point Various aphids  March to June  weak  Nymphs (L3) might assist cleaning up colony remnants in June Lepidosaphis ulmi  Year-round, migration May  likely  Migration is too early, but earwigs can likely feed on settled scales Cacopsylla Pyri   2nd generation: May-June  weak  Earwigs are too late to prevent massive egg-laying and hatching, but L4 can feed on later larval stages   3rd generation onwards  yes  Earwigs can feed on eggs and eclosed larva until October Acknowledgements This research was funded by IWT Agronomic Research grant N° 04-667. We acknowledge collaborating fruit growers, the fruit cooperatives and the Belgian organization for organic farming BELBIOR. References Buxton, J. H. & Madge, D. S. (1976): The evaluation of the European Earwig (Forficula auricularia)as a predator of the damson-hop aphid (Phorodon humuli). I. Feeding experiments. Ent. exp. & appl. 19, 109-114. Carroll, D. P. & Hoyt, S. C. (1984): Augmentation of European earwigs (Dermaptera : Forficulidae) for biological control of apple aphid (Homoptera : Aphididae) in an apple orchard.  J. Econ. Entomol. 77, 738-740. Carroll, D. P., Walker, J. T. S. & Hoyt, S. C. (1985): European earwigs (Dermaptera : Forficulidae) fail  to  control  apple  aphids  on  bearing  apple  trees  and  woolly  apple  aphids  (Homoptera  : Aphididae) in apple rootstock stool beds. Journal of Economic Entomology 78, 972-974. Karsemeijer,  M.  M.  D.  (1973):  Observations  on  the  enemies  of  the  oyster  shell  scale, Lepidosaphes ulmi, on apple in The Netherlands. Journal of Plant Pathology 79, 122-124. Archived at http://orgprints.org/13678/212Lenfant,  C.,  Lyoussoufi,  A.,  Chen,  X.,  D'Arcier,  F.  F.  &  Sauphanor,  B.  (1994):  Potentialités prédatrices  de  Forficula  auricularia  sur  le  psylle  du  poirier  Cacopsylla  pyri. Entomologia Experimentalis et Applicata 73, 51-60. McLeod, J. H. & Chant, D. A. (1952): Notes on the parasitism and food habits of the European earwig, Forficula auricularia L. (Dermaptera : Forficulidae). Canadian Entomologist 84, 343-345.Mueller, T. F., Blommers, L. H. M. & Mols, P. J. M. (1988): Earwig (Forficula auricularia) predation on the woolly apple aphid, Eriosoma lanigerum. Entomol. exp. appl. 47, 145-152. Nicholas, A. H., Spooner-Hart, R. N. & Vickers, R. A. (2005): Abundance and natural control of the woolly aphid Eriosoma lanigerum in an Australian apple orchard IPM program. BioControl 50,271-291.Noppert, F., Smits, J. D. & Mols, P. J. M. (1987): A laboratory, evaluation of the European earwig (Forficula auricularia L.) as a predator of the woolly apple aphid (Eriosoma lanigerum Hausm.). Mededeling Faculteit Landbouwwetenschappen Universiteit Gent 52, 413-422. Phillips, M. L. (1981): The ecology of the common earwig Forficula auricularia in apple orchards. PhD Thesis, University of Bristol, 1-241. .Wirth,  T.,  R.  Le  Guellec,  M.  Vancassel,  and  M.  Veuille.  (1998). Molecular  and  reproductive characterization of sibling species in the European earwig (Forficula auricularia). Evolution, 52:260-265.Archived at http://orgprints.org/13678/

Understanding earwig phenology in top fruit orchards

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