Forceps size and immune function in the earwig Forficula auricularia L.

Females of many species select their mates on the basis of the size or intensity of sexual ornaments, and it has been suggested that these provide reliable signals of a male's ability to resist parasites and pathogens. European earwigs, Forficula auricularia , are sexually dimorphic in forceps shape and length. Male forceps are used as weapons in male contests for access to females, but recent findings suggest that females also choose males on the basis of their forceps length. In the present study, we tested the hypotheses that in the European earwig, F. auricularia , the size of forceps is correlated with immune function and that immune function differs between the sexes. We found that encapsulation rate was not correlated with the length of forceps in either sex, but was negatively correlated with body size. By contrast, lytic activity of the haemolymph increased with overall body size in both sexes but, in females, lytic activity increased with relative forceps length whereas, in males, it decreased with relative forceps length. After accounting for effects of body size, there was no remaining significant correlation in females but the negative correlation in males remained. Furthermore, we found that males had higher encapsulation rate and higher lytic activity than females, suggesting that males have stronger immune defence. The results of the study indicate that the size of forceps in male earwigs does not reliably reflect male immune defence.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 509–516.     

Multiple paternity and mating group size in the European earwig,Forficula auricularia

1. The patterns of multiple paternity among the progeny of females are key properties of genetic mating systems. Female multiple mating should evolve due to direct or indirect benefits, but it may also partly be driven by the encounter rate with different potential mates. 2. In this study this hypothesis was experimentally tested in the European earwig (Forficula auricularia L.) by establishing experimental mating groups that differed in the number of males and females (i.e. density). The number of sires and mean sibling relatedness in each clutch were estimated using microsatellite‐based paternity analysis. 3. As predicted, the mean number of sires per clutch was significantly increased, and sibling relatedness decreased, in the higher density treatment where more potential male mates were available. This change was less than proportional to the number of males in the mating groups, indicating that mechanisms limiting multiple paternity in large mating groups were involved. There were no significant relationships between female reproductive success or male siring success with morphology (body size, weight, and forceps size). 4. The present results show that multiple paternity in F. auricularia clutches is partly determined by the availability of male mates and suggest that this effect is modulated by mechanisms in males and/or females that limit multiple paternity.     

Frass sampling and baiting indicate European earwig (Forficula auricularia) foraging in orchards

Abstract:  Earwigs are significant generalist predators of a range of orchard pests, but quantitative assessment of earwig density and beneficial impact is difficult. A sampling system was designed and tested, based on field placement of polycarbonate tubes in apple trees as scotophase arboreal refugia. Tubes containing artificial diet and provided with a black plastic sleeve had the highest earwig counts. Tubes with diet or the black sleeve alone were less preferred. Presence of distinctive frass was also evident in polycarbonate tubes containing artificial diet, and earwig frass was recorded at a higher frequency than earwig presence, indicating foraging and detection of the tubes at a higher rate than their use as shelters. At the tree level, there was a weak correlation between frass abundance and predation rates on leafroller egg batches placed as baits in the canopy, but not with earwig density measured by corrugated cardboard rolls or diet tubes. Diet tubes have the potential to offer new insights into earwig foraging behaviour in orchards.     

A statistical description of structural variation in the cerci of the common earwig (Forficula auricularia)

Polymorphism in the cerci of the earwig ( Forficula auricularia L.) has been re-examined making use of a graphical method for the analysis of frequency distributions. Three statistically distinct types of male cerci and two statistically distinct types of female cerci are described.     

European earwig (Forficula auricularia) as a novel host for the entomopathogenic nematode Steinernema carpocapsae

The natural history of many entomopathogenic nematode species remains unknown, despite their wide commercial availability as biological control agents. The ambushing entomopathogenic nematode, Steinernema carpocapsae, and the introduced European earwig, Forficula auricularia, forage on the soil surface. Since they likely encounter one another in nature, we hypothesized that earwigs are susceptible to nematode infection. In the laboratory, the LC₅₀ for F. auricularia was 226 S. carpocapsae/earwig and the reproductive potential was 123.5 infective juvenile nematodes/mg tissue. This susceptibility depended on host body size with significantly higher mortality rates seen in larger earwigs. In a study of host recognition behavior, S. carpocapsae infective juveniles responded to earwig cuticle as strongly as they did to Galleria mellonella cuticle. We also found that earwigs exposed to S. carpocapsae cleaned and scratched their front, middle and back legs significantly more than controls. Coupled with previous field data, these findings lead us to suggest that F. auricularia may be a potential host for S. carpocapsae.     

Ontogeny in the European earwig (Forficula auricularia) and grain crops interact to exacerbate feeding damage risk

The preference of herbivores for different host plants can be modulated by plant ontogeny. In agricultural pest management, this has implications for sowing dates and pest monitoring. In the last 20 years, the European earwig (Forficula auricularia), a cosmopolitan pest, has been increasingly implicated in damage to grain crops in Australia. Among these, rapeseed, Brassica napus, appears especially at risk, but little information on F. auricularia as a grain pest is available. We tested the susceptibility of seven grain crops commonly grown in Australia to infestation by F. auricularia using closed microcosm experiments, exposing plant seedlings at two early growth stages to four different life stages of F. auricularia. Lucerne and rapeseed were shown to be the most vulnerable crops, and younger seedlings experienced significantly more damage than older seedlings across all crop types. Fourth instar F. auricularia were found to cause greater feeding damage than younger or older earwigs, while adults collected in winter generally caused more damage than those collected in summer. Surprisingly, even second instar F. auricularia caused greater damage than summer adults. This variation could reflect the ontogenetically dynamic nutritional needs of earwigs. Recent studies of F. auricularia's life cycle in southern Australia indicate that these damaging life stages have some overlap with sowing dates of the crops tested here, exposing their vulnerable seedling stage to infestation. The phenology of F. auricularia in southern Australia therefore partly drives its ability to act as a pest. Future monitoring will likely need to track the distribution of F. auricularia life stages in order to effectively mitigate risks to vulnerable crops.     

Human chromosomal polymorphism

Summary Chromosomal Q polymorphism was studied in 157 adolescents of Yakut nationality (67 males and 90 females) living in Eastern Siberia, on the territory of the Yakut ASSR. Of the 157 subjects, 123 had chromosomal Q variants while 34 (21.7%) had no Q-heterochromatin bands with fluorescence levels 4 and 5. The mean number of Q variants per individual ranged from 0 to 5, with a mean of 1.64. No differences were observed in the frequency of Q variants between sexes. The observed homo- and heteromorph frequencies always agreed with those predicted by the law of Hardy-Weinberg. Of the 157 subjects, four (2.55%) had pericentric inversion of the Q-heterochromatin band in chromosome 3. The following topics are discussed: (1) possible selective value of chromosomal Q-heterochromatin material in the adaptation of human populations to extreme environmental factors, in particular to cold; (2) the taxonomic value of chromosomal Q polymorphism in ethnic anthropology.     

Human chromosomal polymorphism

Chromosomal Q-polymorphism was studied in 198 Kirghiz subjects (98 males and 100 females) from one high-altitude isolate located in the south-eastern part of Kirghizia. Small samples of mountaineers (N = 37) and volunteer subjects (N = 34) were also studied. The samples studied did not differ significantly from each other in the relative frequencies of chromosomal variants in 12 loci of seven Q-polymorphic autosomes. The mean number of Q variants per individual in the populations ranged from 1.3 to 2.0. No sex differences were found in the frequencies of Q variants. The observed homo- and heteromorphic frequencies agreed with those predicted by the law of Hardy-Weinberg. The possible selective value of chromosomal Q heterochromatin material in the adaptation of human populations to high-altitude climate is discussed.     

The invasion biology of the invasive earwig, <Emphasis Type="Italic">Forficula auricularia</Emphasis> in Australasian ecosystems

The European earwig, Forficula auricularia, is a cosmopolitan insect endemic to Europe, West Asia and North Africa, which has invaded many temperate regions of the world including Australia and New Zealand. F. auricularia has been shown to be a complex of morphologically identical, reproductively isolated lineages that possess two distinct clades of mitochondrial DNA. Entomological collection data, historical literature and further field collections were used to develop a greater understanding of Australian F. auricularia’s invasion biology and its current distribution. Genetic analysis of F. auricularia collected from Australia and New Zealand using two mitochondrial genes (COI and a fragment overlapping parts of the COI -COII genes) was also undertaken. To identify the possible source populations of the Australasian invasion these sequences were compared to those from 16 locations within Britain and continental Europe. All Australasian populations were shown to be of the clade B lineage. Tasmanian and New Zealand populations consist of a single subclade comprised of only 4 and 1 haplotypes respectively. The Australian mainland populations also contained a second subclade consisting of up to 11 haplotypes indicating that multiple introductions possibly occurred on the Australian mainland. Comparison of mitochondrial genomes from Australasian and European populations showed the Australian mainland subclade to be most closely related to Portuguese haplotypes, and the Tasmanian and New Zealand clade closely related to those in Brittany, France. No European haplotypes perfectly matched the Australasian sequences. Therefore, the original source populations are still to be identified with harbours on the Iberian Peninsula’s western coast and those on the English Channel likely candidate areas.     

Sex chromosome polymorphism in guppies

Sex chromosomes differ from autosomes by dissimilar gene content and, at a more advanced stage of their evolution, also in structure and size. This is driven by the divergence of the Y or W from their counterparts, X and Z, due to reduced recombination and the resulting degeneration as well as the accumulation of sex-specific and sexually antagonistic genes. A paradigmatic example for Y-chromosome evolution is found in guppies. In these fishes, conflicting data exist for a morphological and molecular differentiation of sex chromosomes. Using molecular probes and the previously established linkage map, we performed a cytogenetic analysis of sex chromosomes. We show that the Y chromosome has a very large pseudoautosomal region, which is followed by a heterochromatin block (HCY) separating the subtelomeric male-specific region from the rest of the chromosome. Interestingly, the size of the HCY is highly variable between individuals from different population. The largest HCY was found in one population of Poecilia wingei, making the Y almost double the size of the X and the largest chromosome of the complement. Comparative analysis revealed that the Y chromosomes of different guppy species are homologous and share the same structure and organization. The observed size differences are explained by an expansion of the HCY, which is due to increased amounts of repetitive DNA. In one population, we observed also a polymorphism of the X chromosome. We suggest that sex chromosome-linked color patterns and other sexually selected genes are important for maintaining the observed structural polymorphism of sex chromosomes.     

A bacterial genetic screen identifies functional coding sequences of the insect mariner transposable element Famar1 amplified from the genome of the earwig, Forficula auricularia

Transposons of the mariner family are widespread in animal genomes and have apparently infected them by horizontal transfer. Most species carry only old defective copies of particular mariner transposons that have diverged greatly from their active horizontally transferred ancestor, while a few contain young, very similar, and active copies. We report here the use of a whole-genome screen in bacteria to isolate somewhat diverged Famar1 copies from the European earwig, Forficula auricularia, that encode functional transposases. Functional and nonfunctional coding sequences of Famar1 and nonfunctional copies of Ammar1 from the European honey bee, Apis mellifera, were sequenced to examine their molecular evolution. No selection for sequence conservation was detected in any clade of a tree derived from these sequences, not even on branches leading to functional copies. This agrees with the current model for mariner transposon evolution that expects neutral evolution within particular hosts, with selection for function occurring only upon horizontal transfer to a new host. Our results further suggest that mariners are not finely tuned genetic entities and that a greater amount of sequence diversification than had previously been appreciated can occur in functional copies in a single host lineage. Finally, this method of isolating active copies can be used to isolate other novel active transposons without resorting to reconstruction of ancestral sequences.     

Dispersal of single‐ and double‐brood populations of the European earwig,Forficula auricularia: a mark‐recapture experiment

Quantitative information on dispersal of insects should be taken into consideration for making efficient pest management decisions. Such information was not available for the European earwig, Forficula auricularia L. (Dermaptera: Forficulidae), an important biocontrol agent in fruit orchards. A mark‐recapture experiment was carried out in Belgian orchards, where marked earwigs were released at a single point and recaptured after 1 month. Dispersal from this release point was analysed using an analytical formula of a simple diffusion model with disappearance (e.g., as a result of death) derived by Turchin & Thoeny (1993; Quantifying dispersal of southern pine beetles with mark‐recapture experiments and a diffusion model. Ecological Applications 3: 187) . The cumulative number of recaptured earwigs as a function of the distance of release was used to fit the model and estimate parameters. A derived expression, in terms of these parameters, was used to estimate the frequency distribution of the population, as the radius of a circle enclosing various proportions of the earwigs’ dispersal distances. In Belgium, populations of the European earwig can have two life‐history strategies, single‐ (SBP) and double‐brood populations (DBP). Therefore, mark‐recapture experiments were carried out on both population types. We fitted data from SBP (n = 10) and DBP (n = 16) successfully in both the diffusion model and in an exponential curve. Because of the biological relevance, estimates of the diffusion model were used for calculating the frequency distributions. Males and females dispersed the same distances. No differences were found between orchards with different spatial structures (apple and pear). According to literature data, mobility of earwigs is very low compared with other arthropods, which has consequences for the efficiency of biocontrol interventions, like mass releases of earwigs or the use of hedgerows for the establishment of healthy (source) populations. Quantitative results revealed that earwigs of SBP dispersed four times further than earwigs of double‐brood populations. For instance, 95% of the population remained within a radius of 28.6 m in SBP and 7.54 m in DBP.     

Biology and host range testing of Triarthria setipennis and Ocytata pallipes (Diptera: Tachinidae) for the control of the European earwig (Forficula auricularia)

The European earwig (Forficula auricularia) is an invasive species in the Falkland Islands, causing considerable problems for local horticulture, as well threatening indigenous ecosystems. To assess the potential of a classical biological control introduction two parasitoid fly species, Triarthria setipennis and Ocytata pallipes (Diptera: Tachinidae), were collected from sites in southern and northern England and then tested for their suitability as earwig biological controls at Egham, UK. Both species had previously been introduced into North America for earwig control however little is known of their long-term efficacy and host specificity. Host range tests including both target and non-target species were done. As there are no native Dermaptera on the Falkland Islands, tests were restricted to the field cricket Gryllus assimilis and the Dubia cockroach Blaptica dubia, as representatives of insect orders phylogenetically closely related to earwigs. A second cricket species (Gryllus bimaculatus) was included in an egg-depositing experiment for O. pallipes. Both tachinid species successfully parasitised and emerged from earwigs under laboratory conditions but no signs of parasitisation and development were observed in either the cricket or cockroach.     

Human chromosomal polymorphism. V. Chromosomal Q polymorphism in African populations

Summary The distribution pattern of Q-heterochromatin variants in seven autosomes (3, 4, 13–15, 21, and 22) was studied in three aboriginal Negroid populations of Africa (Mozambique, Angola, and Ethiopia). It was shown that among African Negroids there are no individuals completely lacking Q-heterochromatin bands with fluorescence levels 4 and 5. The mean number of Q variants per individual was 3.47, 4.80, and 4.85 in the Ethiopian, Mozambique, and Angola populations, respectively. The observed homo- and heteromorphic frequencies always agreed with those predicted by the law of Hardy-Weinberg. The populations of tropical lowland Negroids (Mozambique and Angola) proved to be significantly homogeneous both in the frequency of Q variants and the mean number of these variants per individual, so they were examined as a single group. However, comparative analysis of highland (Ethiopians) and lowland Negroids revealed statistically significant differences. The following questions are discussed: (1) the possible selective value of chromosomal Q heterochromatin material in the adaptation of human populations to high-altitude climate; (2) the possible existence of intraracial heterogeneity in Negroids living in different ecological zones of Africa; (3) the possible taxonomic value of an inverted Q-heterochromatin band in chromosome 3 in ethnic anthropology.     

Temperature sensitivity of chromosomal polymorphism inDrosophila pseudoobscura

Population cages ofDrosophila pseudoobscura with the gene arrangements Arrowhead and Chiricahua (CH) were studied at 15 1/2°, 17 1/2°, 19°, 22°C, and a fluctuating temperature (F°) ranging from 17° to 27° with mean of 22°. At the three lower temperatures there were only small but detectable changes in the frequency of CH, but at 22° and F° the earlier populations (V and K) showed the elimination of CH and the later ones (W and L) showed an equilibrium similar to that at 25°. Evidence is presented to show that an environmental change strongly affecting population size need have no effect on the inversion system. Several environmental factors that could have influenced the results are discussed.The temperature sensitivity of the inversion system is discussed in relation toWright's adaptive surface model of genotypes. It is proposed that at about 22° there are a number of narrowly separated steep-sided peaks, some of which represent polymorphic and others monomorphic genetic systems. At 25° the surface has a single peak favoring inversion polymorphism, while from 15° to 19° no well-defined peaks are discernible.Dedicated to Prof. L. C. Dunn in friendship and in recognition of his many contributions to the science of genetics.National Science Foundation (U.S.A.) Predoctoral Fellow, 1956–1959; Columbia University Fellow, 1959–1960; Boese Postdoctoral Fellow, Columbia University, 1961–1962.