Ecological Entomology

WETTERER, JAMES K.; ESPADALER, XAVIER; WETTERER, ANDREA L.; AGUIN‐POMBO, DORA; FRANQUINHO‐AGUIAR, ANTÓNIO M.

doi: 10.1111/j.1365-2311.2006.00790.xpmid: N/A

Abstract 1. The earliest exotic records for two notorious invasive ants, the big‐headed ant (Pheidole megacephala) and the Argentine ant (Linepithema humile), both come from the Atlantic islands of Madeira, where the two species underwent population explosions in the 1850s and 1890s respectively. Researchers have long assumed that these invaders spread across all of Madeira and exterminated most or all native ants, despite no research actually documenting such impact. 2. Re‐examination of first‐hand nineteenth century accounts suggest that P. megacephala and L. humile may never have spread beyond coastal lowland areas, representing < 10% of Madeira’s land area. In 2002, native ants dominated most of Madeira; P. megacephala and L. humile were restricted to ≈ 0.3% and ≈ 6% of Madeira’s land area respectively. 3. Of the 10 native ant species known from Madeira, only one (Temnothorax wollastoni) was not present in 1999–2002 surveys. Although exotic ants may have exterminated T. wollastoni, it seems likely that this species still survives. 4. Thus, even after 150 or more years of residence, P. megacephala and L. humile have come to occupy only a small part of Madeira, and appear to have had little impact. 5. Most of Madeira may be too cool for P. megacephala and perhaps too moist for L. humile to dominate. Also, Madeira’s vast natural areas may generally lack weedy vegetation that can support high densities of plant‐feeding Hemiptera critical for the ecological dominance of invasive ants. Finally, a dominant native ant, Lasius grandis, inhabiting ≈ 84% of Madeira, may actively exclude P. megacephala and L. humile.

PHILPOTT, STACY M.; ARMBRECHT, INGE

doi: 10.1111/j.1365-2311.2006.00793.xpmid: N/A

Abstract 1. Intensive agricultural practices drive biodiversity loss with potentially drastic consequences for ecosystem services. To advance conservation and production goals, agricultural practices should be compatible with biodiversity. Traditional or less intensive systems (i.e. with fewer agrochemicals, less mechanisation, more crop species) such as shaded coffee and cacao agroforests are highlighted for their ability to provide a refuge for biodiversity and may also enhance certain ecosystem functions (i.e. predation). 2. Ants are an important predator group in tropical agroforestry systems. Generally, ant biodiversity declines with coffee and cacao intensification yet the literature lacks a summary of the known mechanisms for ant declines and how this diversity loss may affect the role of ants as predators. 3. Here, how shaded coffee and cacao agroforestry systems protect biodiversity and may preserve related ecosystem functions is discussed in the context of ants as predators. Specifically, the relationships between biodiversity and predation, links between agriculture and conservation, patterns and mechanisms for ant diversity loss with agricultural intensification, importance of ants as control agents of pests and fungal diseases, and whether ant diversity may influence the functional role of ants as predators are addressed. Furthermore, because of the importance of homopteran‐tending by ants in the ecological and agricultural literature, as well as to the success of ants as predators, the costs and benefits of promoting ants in agroforests are discussed. 4. Especially where the diversity of ants and other predators is high, as in traditional agroforestry systems, both agroecosystem function and conservation goals will be advanced by biodiversity protection.

CHAPMAN, JASON W.; REYNOLDS, DON R.; BROOKS, STEPHEN J.; SMITH, ALAN D.; WOIWOD, IAN P.

doi: 10.1111/j.1365-2311.2006.00797.xpmid: N/A

Abstract 1. Insect migration strategies are generally poorly understood due to the propensity for high‐altitude flight of many insect species, and the technical difficulties associated with observing these movements. While some progress has been made in the study of the migration of important insect pests, the migration strategies of insect natural enemies are often unknown. 2. Suction trapping, radar monitoring, and high‐altitude aerial netting were used to characterise the seasonal migrations in the U.K. of an assemblage of aphid predators: three green lacewings in the Chrysoperla carnea species complex. 3. Chrysoperla carnea sens. str. was found to be very abundant at high altitudes during their summer migration, and some individuals were capable of migrating distances of ≈ 300 km during their pre‐ovipositional period. In contrast, high‐altitude flights were absent in the autumn migration period, probably due to a behavioural adaptation that increases the probability that migrants will encounter their over‐wintering sites. The other two species in the complex, C. lucasina and C. pallida, were much rarer, making up ≈ 3% of the total airborne populations throughout the study period. 4. The summer migration of C. carnea sens. str. was not directly temporally associated with the summer migration of its cereal aphid prey, but lagged behind by about 4 weeks. There was also no evidence of spatial association between aphid and lacewing populations. 5. The results show that to understand the population ecology of highly mobile insect species, it is necessary to characterise fully all aspects of their migration behaviour, including the role of high‐altitude flights.

WESTPHAL, CATRIN; STEFFAN‐DEWENTER, INGOLF; TSCHARNTKE, TEJA

doi: 10.1111/j.1365-2311.2006.00801.xpmid: N/A

Abstract 1. The study tested the hypotheses that bumblebees have shorter foraging trips in environments that provide abundant resources than in environments that provide sparse resources, and that shorter foraging trips translate into greater colony growth. 2. Six even‐aged Bombus terrestris colonies were established in contrasting resource environments. Three colonies had access to abundant resources (Phacelia tanacetifolia fields with high flower densities), and three colonies were placed in an environment with sparse resources (scattered semi‐natural habitats with food plants at lower densities). 3. A total of 870 foraging trips of 220 marked B. terrestris foragers were observed using automated camcorder recordings. 4. The duration of foraging trips was shorter in environments with abundant resources (66 ± 4.6 min) than in environments with sparse resources (82 ± 3.7 min). Within 34 days colonies that had access to abundant resources gained significantly more weight (129 ± 40 g) than colonies foraging on sparse resources (19 ± 7 g). 5. Thus, the spatial distribution and quality of resources at landscape level affected the duration of foraging trips and the colony growth. It was concluded that future conservation schemes need to improve the spatial and temporal availability of resources in agricultural landscapes to counteract the ongoing decline of bumblebees.

JOHNSON, SCOTT N.; BIRCH, A. NICHOLAS E.; GREGORY, PETER J.; MURRAY, PHILIP J.

doi: 10.1111/j.1365-2311.2006.00776.xpmid: N/A

Abstract 1. Few entomological studies include soil‐dwelling insects in mainstream ecological theory, for example the preference–performance debate. The preference–performance hypothesis predicts that when insect herbivores have offspring with limited capacity to relocate in relation to a host plant, there is a strong selection pressure for the adult to oviposit on plants that will maximise offspring performance. 2. This paper discusses the proposition that insect herbivores that live above ground, but have soil‐dwelling offspring, should be included in the preference–performance debate. Twelve relevant studies were reviewed to assess the potential for including soil insects in this framework, before presenting a preliminary case study using the clover root weevil (Sitona lepidus) and its host plant, white clover (Trifolium repens). 3. Maternal S. lepidus preferentially oviposited on T. repens plants that had rhizobial root nodules (which enhance offspring performance) rather than T. repens plants without nodules, despite plants having similar foliar nutritional quality. This suggests that adult behaviour above ground was influenced by below‐ground host‐plant quality. 4. A conceptual model is presented to describe how information about the suitability for offspring below ground could underpin oviposition behaviour of parental insects living above ground, via plant‐ and soil‐mediated semiochemicals. These interactions between genetically related, but spatially separated, insect herbivores raise important evolutionary questions such as how induced plant responses above ground affect offspring living below ground and vice versa.