Overige insecten

Western culture views insects and arachnids as pests and vermin that need to be controlled. They usually are not considered as something to be preserved. Accordingly, arthropods and other small organisms have not been taken seriously for conservation by policy makers and the conservation community at large. Arthropods, however, are major components of diverse ecosystems and are the major players in functioning of ecosystem processes. Arthropods are relentlessly vanishing before our eyes. They must be preserved because of their inherent values but also because we need them for human survival.

An article by Bird Studies Canada biologist Jon McCracken examines substantial population declines for ‘aerial insectivores ‘ – birds that specialize on feeding on flying insects. The alarming trend, which appears to be most pronounced in Canada, has been revealed by the analysis of results from several bird monitoring programs, including the newly released Atlas of the Breeding Birds of Ontario, 2001-2005 and the North American Breeding Bird Survey.

According to the latest update of "The Atlas of the Breeding Birds of Ontario" the list of songbird species in Ontario that are declining is staggering. "Population trends are generally positive for birds of prey, but biologists are expressing concern about the fate of grassland birds and those that feed on flying insects," says a statement from the organizers of the survey that led to the first update in 20 years.

Sacramento’s remnant population of the Purple Martin Progne subis, a swallow recognized as a state Species of Special Concern, declined again in 2008 according to a recent survey. The number of nesting martins declined to 84 nesting pairs, a 21% decline from last year. The population is at the lowest level recorded since surveys were initiated in the early 1990s. The continued population decline in Sacramento worries biologist Dan Airola, who has been studying and managing the purple martin population for years with a group of dedicated volunteers. “Over the last 4 years, the population has decreased by over 50%, which is pretty dramatic” Airola notes.

There is growing concern about increased population, regional, and global extinctions of species. A key question is whether extinction rates for one group of organisms are representative of other taxa. We present a comparison at the national scale of population and regional extinctions of birds, butterflies, and vascular plants from Britain in recent decades. Butterflies experienced the greatest net losses, disappearing on average from 13% of their previously occupied 10-kilometer squares. If insects elsewhere in the world are similarly sensitive, the known global extinction rates of vertebrate and plant species have an unrecorded parallel among the invertebrates, strengthening the hypothesis that the natural world is experiencing the sixth major extinction event in its history.

There is continuing debate about the impact of agricultural practices on farmland wildlife. In particular, it has been postulated that a general decline in insect abundance linked with intensification of agriculture may have contributed to farmland bird decline. While some autecological studies have supported this hypothesis, larger-scale and long-term studies are needed.

• Suction traps mounted on 12·2-m towers (Rothamsted-type) have been sampling aerial insects for nearly 40 years throughout the UK. Their catches are correlated over large spatial scales. We analysed insect catch data from a single suction trap run for 27 years in a rural location in Scotland, and showed that insect numbers have changed significantly over time, although non-linearly. The multivariate data set (numbers from the 12 common arthropod groups) was summarized using principal components analysis (PCA) to extract three components explaining 62% of the variation.

• We also used PCA to describe agricultural change, using published agricultural data for eight measures of farming in Scotland. Arthropod abundance and principal component (PC) scores were significantly related to the agricultural PC scores as well to summary climatic measures.

• Using Scottish data from the British Trust for Ornithology Common Birds Census, we extracted three PC to describe the time-dependent average densities of 15 common farmland birds in Scotland. Measures of bird density were significantly related to insect abundance and PC scores and, independently, to measures of agriculture and climate.

• These data from a broad suite of species provide support for linked temporal change between farmland birds, invertebrate numbers and agricultural practice in Scotland. Although entirely correlative, the results are consistent with the view that agricultural change has influenced birds through changes in food quality or quantity. The work also shows how large-scale invertebrate sampling, in this case using suction traps, is useful for monitoring farmland biodiversity.