Introduction: key threats to insects

Habitat change is the predominant threat to many insects and is often that most easily observed. It is potentially universal. Countering and repairing habitat changes that have occurred through loss or degradation is therefore the primary focus of conservation management for almost all species of concern. However, a variety of other concerns may arise, and in some cases one or more of these become central themes for management to address. Each has had major importance in some insect management plans, and they are noted here to exemplify some of the problems that may arise, and to ensure that they are not overlooked in planning. However, unlike habitat considerations, they may not be a factor in every programme. Conversely, they may be highly important. When they are present, as with changes to habitats, they may either cause direct mortality or affect the quality of the environment within which the species dwells. Some causes of direct mortality of insects are very difficult to anticipate and may not be obvious until closely investigated. USFWS (2001) summarised information for a dragonfly to suggest that mortality from direct impacts with vehicles or trains may contribute to reducing population size, for example. In Illinois, railways pass close to or through three of the sites supporting the largest populations of Hine's emerald dragonfly. At two of these sites, train speeds are reduced to only c. 6–10 km h-1 during the dragonfly flight season (Soluk et al. 1998), as a measure to reduce impact mortality.