Ian P. Woiwod

Climate change and trophic interactions

With confirmation of anthropogenically induced climate change, the spotlight is on biologists to predict and detect effects on populations. The complexity of interactions within and between the biotic and abiotic components involved makes this a tough challenge, and most studies have consequently considered effects of only single climate variables on single species. However, some have gone further, and recently published long-term datasets now offer opportunities that complement new experimental approaches that span trophic levels. With these datasets, predicting relative shifts in temporal and spatial associations could be among the most tractable problems.

Spatial synchrony in the dynamics of moth and aphid populations

1. We report patterns of intraspecific spatial synchrony (cross-correlation with lag zero) in the dynamics of British moths and aphids sampled at 57 and 21 localities throughout the UK. 2. Spatial synchrony was substantially higher in aphids than in moths. In both taxa, spatial synchrony declined with increasing distance between conspecific populations, but synchrony remained positive at all distances up to 800 km. 3. Species with large slopes (>2) of the spatial variance-mean regression had spatially asynchronous dynamics, as predicted by a theoretical model. 4. In noctuid moths and in aphids, but not in geometrid moths, there was a significant positive correlation between the degree of spatial synchrony and the level of temporal variability in local populations. 5. We discuss the two main hypotheses about the causes of spatial synchrony, migration and regional stochasticity (spatially correlated weather conditions). We conclude that our results on large-scale spatial synchrony in moths and aphids are better explained by regional stochasticity than by migration.

Climate change impacts on insect management and conservation in temperate regions: can they be predicted?

Global environmental change is amongst the greatest long-term threats to humans. We need suf®cient food, clean air and a comfortable environment in which to live and our current way of life threatens all of these. We have thrived as a result of the major changes that we have imposed on the planet, particularly with respect to clearing space for modern agriculture and the development and use of related technologies. However, we now understand suf®ciently the nature of interactions and feedbacks within and between abiotic and biotic components of the environment to realize the potential dangers from perturbation of any of these components. Insects are the most diverse class of organisms on Earth (May, 1990). As insects have many detrimental and bene®cial effects on humans and natural ecosystems, both directly and indirectly, it is not surprising that considerable thought has already been given to the impacts that global environmental change may have on them (e.g. Porter et al., 1991; Cammell & Knight, 1992; chapters in Kareiva et al., 1993; chapters in Harrington & Stork, 1995; Patz & Martens, 1996; Cannon, 1998; Epstein, 2000; Rogers & Randolph, 2000). The reason for trying to predict the impacts of climate change within the context of agriculture and forestry is to help to determine whether present systems will be sustainable. Relevant questions include: will we be able to manage insects and their habitats in the future the way we do today and, if not, what can we do about it; will we need to consider every insect in every situation independently or is there any hope of generalizing; can we expect to develop adequately predictive process-based models of change, and can statistical analyses of long-term data lead to useful predictions? This paper is concerned mainly with predicting the effects of climate change on insect pests and bene®cial insects of agriculture and forestry in the northern hemispheres temperate zones, although the general principles may be applied more widely. Whilst mindful of interactions with other factors, we concentrate mainly on temperature because, of the climate variables, it is the one for which there is most con®dence in predictions of future climate change scenarios (Houghton et al., 2001) and for which we have most evidence from which predictions of impacts might be derived. The potential rate of increase of many insects is strongly dependent on temperature, and their survival is impaired at low and high temperatures. Changes in both mean temperature and the extent and frequency of extremes can hence have major impacts on insect populations. First we outline what one might intuitively expect to happen to insects as a result of a general rise in temperature and then we look at various complicating factors that have the potential to confound these expectations. Next we give examples of changes that are already occurring and are consistent with expectation. Finally we consider some of the possible implications of these changes for insect pest management and insect conservation.

High‐altitude migration of the diamondback moth Plutella xylostella to the U.K.: a study using radar, aerial netting, and ground trapping

Abstract 1. The high‐altitude wind‐borne migration of the diamondback moth Plutella xylostella in the U.K. in 2000 was investigated (a) by direct monitoring of insect flight by vertical‐looking radar and by aerial netting, and (b) through evidence of temporal variation in P. xylostella abundance deduced from a network of light traps.

A novel approach to the use of genetically modified herbicide tolerant crops for environmental benefit

The proposed introduction of genetically modified herbicide tolerant (GMHT) crops, with claims of improved weed control, has prompted fears about possible environmental impacts of their widespread adoption, particularly on arable weeds, insects and associated farmland birds. In response to this, we have developed a novel weed–management system for GMHT sugar beet, based on band spraying, which exploits the flexibility offered by the broad–spectrum partner herbicides. Here, we show the results from two series of field experiments which, taken together, demonstrate that, by using this system, crops can be managed for enhanced weed and insect biomass without compromising yield, thus potentially offering food and shelter to farmland birds and other wildlife. These results could be applicable widely to other row crops, and indicate that creative use of GMHT technology could be a powerful tool for developing more sustainable farming systems in the future.

Diversity and abundance of the coleopteran fauna from organic and conventional management systems in southern England

1 Studies of the epigeal coleopteran fauna on five pairs of organic and conventional farms were carried out between May and July 1994 in southern England using pitfall trapping. A total of 27 749 individuals and 140 species were identified. Overall, abundance of Coleoptera was greatest on organically managed farms.

What drives community dynamics

The search for general mechanisms of community assembly is a major focus of community ecology. The common practice so far has been to examine alternative assembly theories using dichotomist approaches of the form neutrality versus niche, or compensatory dynamics versus environmental forcing. In reality, all these mechanisms will be operating, albeit with different strengths. While there have been different approaches to community structure and dynamics, including neutrality and niche differentiation, less work has gone into separating out the temporal variation in species abundances into relative contributions from different components. Here we use a refined statistical machinery to decompose temporal fluctuations in species abundances into contributions from environmental stochasticity and inter-/intraspecific interactions, to see which ones dominate. We apply the methodology to community data from a range of taxa. Our results show that communities are largely driven by environmental fluctuations, and that member populations are, to different extents, regulated through intraspecific interactions, the effects of interspecific interactions remaining broadly minor. By decomposing the temporal variation in this way, we have been able to show directly what has been previously inferred indirectly: compensatory dynamics are in fact largely outweighed by environmental forcing, and the latter tends to synchronize the population dynamics.

An aerial netting study of insects migrating at high altitude over England

Day and night sampling of windborne arthropods at a height of 200 m above ground was undertaken at Cardington, Bedfordshire, UK, during July 1999, 2000 and 2002, using a net supported by a tethered balloon. The results from this study are compared with those from the classic aerial sampling programmes carried out by Hardy, Freeman and colleagues over the UK and North Sea in the 1930s. In the present study, aerial netting was undertaken at night as well as daytime, and so the diel periodicity of migration could be investigated, and comparisons made with the results from Lewis and Taylors extensive survey of flight periodicity near ground level. In some taxa with day-time emigration, quite large populations could continue in high-altitude flight after dark, perhaps to a previously underrated extent, and this would greatly increase their potential migratory range. Any trend towards increases in night temperatures, associated with global warming, would facilitate movements of this type in the UK. Observations on the windborne migration of a variety of species, particularly those of economic significance or of radar-detectable size, are briefly discussed.

Effects on weed and invertebrate abundance and diversity of herbicide management in genetically modified herbicide-tolerant winter-sown oilseed rape

We evaluated the effects of the herbicide management associated with genetically modified herbicide-tolerant (GMHT) winter oilseed rape (WOSR) on weed and invertebrate abundance and diversity by testing the null hypothesis that there is no difference between the effects of herbicide management of GMHT WOSR and that of comparable conventional varieties. For total weeds there were few treatment differences between GMHT and conventional cropping, but large and opposite treatment effects were observed for dicots and monocots. In the GMHT treatment, there were fewer dicots and more monocots than in conventional crops. At harvest, dicot biomass and seed rain in the GMHT treatment were one-third of that in the conventional, while monocot biomass was threefold greater and monocot seed rain almost fivefold greater in the GMHT treatment than in the conventional. These differential effects persisted into the following two years of the rotation. Bees and butterflies that forage and select for dicot weeds were less abundant in GMHT WOSR management in July. Year totals for Collembola were greater under GMHT management. There were few other treatment effects on invertebrates, despite the marked effects of herbicide management on the weeds.

Development of vertical-looking radar technology for monitoring insect migration

Abstract The development of vertical-looking radar (VLR) has allowed long-term monitoring of the altitudinal and temporal dynamics of high-flying insect populations to be a practical proposition for the first time. The system also provides a unique insight into the behaviour of migrating insects. A new analysis routine for estimating body mass of over-flying insects is described. Procedures for calculating the maximum range of detection for insects of different sizes and the volume of air sensed by the VLR have also been developed. Sample data of diurnal patterns of activity, temporal variation of abundance and density–height profiles of aerial insect populations are presented.