Ecological Entomology

CRAWLEY, M. J.; PATTRASUDHI, R.

doi: 10.1111/j.1365-2311.1988.tb00352.xpmid: N/A

ABSTRACT. 1 Removal field experiments and observational studies have been undertaken to determine whether feeding by cinnabar moth Tyria jacobaeae L. on the flower heads of ragwort Senecio jacobaea L. affects the abundance of the fly Pegohylemyia seneciella (Meade) that feeds in the flower heads as a larva. 2 Correlations between the population density of cinnabar moth and the population density of the fly were suggestive of habitat separation, but provided little evidence of exploitation competition. 3 Removal of cinnabar moth by hand from replicated plots over two years shows that, in years when ragwort flower production is consumed by cinnabar moth caterpillars, the fly may show no recruitment at all. 4 Fly populations persist in refugia, exploiting ragwort plants that grow in areas where there are no cinnabar moth. 5 Recruitment of ragwort is not seed limited, so the reduction in seed production caused by P. seneciella (maximum about 30%) has no impact on ragwort abundance, or on the abundance of cinnabar moth. 6 We conclude that there is strong interspecific competition between these two species, and that the competition is highly asymmetric. The cinnabar moth had a substantial effect on the recruitment of the fly in 1986, but the fly has no measurable impact on the recruitment of the moth. In six years out of seven in our long‐term study, cinnabar moth reduced flower production to levels comparable to those measured in 1986, and we infer that strong competition with the fly was likely in six years out of seven. 7 One reason why there are so few published examples of asymmetric interspecific competition may be simply that the experiments are thought too obvious to be worth doing. We argue that this is not a good reason for eschewing manipulative field experiments, and that few processes in ecology are at all obvious when investigated in detail.

doi: 10.1111/j.1365-2311.1988.tb00353.xpmid: N/A

Book Reviewed in this Article:

DOUBE, B. M.; GILLER, P. S.; CSIRO, F. MOOLA

doi: 10.1111/j.1365-2311.1988.tb00354.xpmid: N/A

ABSTRACT. 1 The dung colonization and dung burial behaviour of twelve crepuscular/nocturnal tunnelling (paracoprid) species of beetles were examined in order to identify mechanisms which might facilitate resource (dung) partitioning. The species were selected from a diverse assemblage of dung beetles, the members of which coexist in the sandy‐soil regions of Natal, South Africa. 2 The pattern of dung colonization in relation to dung age was examined in the field using baited pitfall traps. Some species, e.g. Onitis deceptor Peringuey, Catharsius tricornutus De Geer and Copris elphenor Klug, showed a marked preference for fresh dung (1–2 days old) whereas other species, e.g. O. viridulus Boheman and Copris fallaciosus Gillet, preferred older dung (3–7 days old). 3 Two distinct patterns of dung burial were recognized. In the Coprini, dung burial was complete within 24–48h of pad colonization, and the level of dung burial was similar in the laboratory and in the field. In the Onitini, dung burial occurred progressively over a 12‐day period, although the timing of initiation of dung burial varied between species: in O. deceptor nearly all individuals had begun burial within 2 days of pad colonization, whereas only 20% of O. viridulus had commenced dung burial by that time. However, nearly all O. viridulus had buried substantial quantities of dung by day 12. 4 The mass of dung buried per pair by the larger coprine beetles (100–300 g) and onitine beetles (400–1000 g) suggests that there is potential for inter‐ and intraspecific competition, even in pads colonized by relatively few beetles. The colonization and use of dung of different ages are discussed as means of resource partitioning in relation to the relative abilities of species to compete for dung.

doi: 10.1111/j.1365-2311.1988.tb00355.xpmid: N/A

Book Reviewed in this Article:

EDGERLY, JANICE S.

doi: 10.1111/j.1365-2311.1988.tb00356.xpmid: N/A

ABSTRACT. 1 The life cycle of Antipaluria urichi (Saussure) (Embiidina: Clothodidae) was aseasonal and without overlap of generations within fifteen closely monitored colonies observed over a 9½ month field season. Adult females remained with their nymphs after hatch but disappeared prior to maturation of their offspring. 2 Time budgets of nymphs and their mothers differed significantly. Adult females spent significantly more time spinning silk than their offspring. After the nymphs hatched, the increase in area of the silk covering approximated an exponential curve, reflecting the increase in silk spinning behaviour exhibited by the adult female. These results indicate that silk may be a major contribution of the mother. 3 Observations suggest that silk protects embiids from some predators and from rainfall, which is often torrential in the rainforest. 4 In experimental field colonies, nymphs with their mothers developed significantly faster than those alone, indicating that maternal behaviours promote the development of their nymphs.

FAIRBAIRN, DAPHNE J.

doi: 10.1111/j.1365-2311.1988.tb00357.xpmid: N/A

ABSTRACT. 1 Gerris remigis Say (Hemiptera; Gerridae) is primarily apterous, but populations with up to 33% macropters have been reported. The macropters seldom fly, and field studies have revealed no detectable differences between wing morphs in movement or survival at any time of year. 2 In this paper, life history traits of macropterous and apterous G. remigis are compared in an attempt to determine the mechanisms responsible for the maintenance of macroptery in this species in spite of the very low flight capacity and infrequent flight of macropters. 3 Development time, proportion breeding without diapause, and overwinter survival do not differ between morphs. However, pre‐diapause macropterous females have a significantly shorter pre‐oviposition period than apterous females. In contrast, post‐diapause macropters begin reproducing later than apters, and have a lower cumulative fecundity. 4 These results suggest that macropters may be at a selective advantage in warm habitats which favour pre‐diapause reproduction, but that apters should be favoured in the preferred, cool, lotic habitats. 5 However, crossing and rearing experiments indicate that wing morphology is primarily environmentally controlled in this species, and that the heritability of wing morphology is low, at best. In light of this, the relative impacts of purely phenotypic (environmental) variation, random effects, and the observed fitness differences on the maintenance of macroptery in this species are discussed.

GODFRAY, H. C. J.

doi: 10.1111/j.1365-2311.1988.tb00358.xpmid: N/A

ABSTRACT. 1 The fig wasps inhabiting the figs of Ficus hispidioides S. Moore in New Guinea were investigated. The galls formed by the pollinating agaonid were also inhabited by two other non‐pollinating species of wasp; a third non‐pollinating wasp caused the production of a different type of gall, and was itself parasitized by a fourth species. In all species, males were wingless and all matings occurred within the fig. 2 It was estimated that 2% of the pollinating fig wasps left the fig unmated. The equivalent figures for three of the non‐pollinating wasps were 2%, 4% and 23%. The significance of oviposition by virgin females to the sex allocation strategy of mated females is discussed. 3 The absence of fighting and male wing dimorphism were studied in the context of the predictions of their occurrence by Hamilton (1979).

HALSALL, NIGEL B.; WRATTEN, STEPHEN D.

doi: 10.1111/j.1365-2311.1988.tb00359.xpmid: N/A

ABSTRACT. 1 The efficiency of pitfall trapping was investigated for seven carabid species, using time‐lapse video recording equipment, in the laboratory. 2 The effects of differing substrates, trap designs and seasons of collection on the capture rates of the carabids was also investigated. 3 Capture rate differed significantly between the species studied. The differences in capture rates between the species were unrelated to beetle size, speed of movement and diurnal behaviour. 4 Few differences arose in the capture rates when type of substrate or trap or season of capture were changed.

HAWKINS, BRADFORD A.

doi: 10.1111/j.1365-2311.1988.tb00360.xpmid: N/A

ABSTRACT. 1 The hypothesis that leaf‐chewing caterpillars and leaf miners indirectly compete via the influence of foliar damage on parasitoids was experimentally tested using the leaf miner Coleophora serratella (L.) and a complex of folivorous caterpillars on birch. 2 Separate experiments tested the effects of manipulating artificial or caterpillar‐induced leaf damage on parasitism of leaf miners at several spatial scales. 3 Parasitism of C. serratella by specialist and generalist parasitoids was independent of the extent of either collateral or leaf‐miner damage, whether experimentally or naturally induced. 4 Support in the literature for the hypothesis is restricted to a single case, and only on a limited spatial scale; thus, the idea that collateral damage directs parasitoid‐mediated competition among herbivores remains highly speculative.

JONES, T. H.; HASSELL, M. P.

doi: 10.1111/j.1365-2311.1988.tb00361.xpmid: N/A

ABSTRACT. 1 The spatial patterns of parasitism of the cabbage root fly caused by the cynipid parasitoid Trybliographa rapae (Westw.) have been studied in a laboratory system, within field cages and in a natural situation. 2 Continuous observations during the laboratory experiments showed the parasitoids to spend proportionately more time on the patches of high host density. This resulted in the per cent parasitism per patch being directly density dependent. 3 Similar patterns of parasitism were found from the field cage system, and also from experiments using the natural parasitoid population and either manipulated or natural host densities. 4 While mutual interference was marked in the laboratory experiments, there was little or no sign of it within the larger field cages.