Insecticides

The hemlock woolly adelgid (HWA), a native of Asia, a 1/32 inch long reddish purple insect that lives within its own protective coating, is a threat to eastern hemlock forests, and eastern and Carolina hemlock of all sizes are susceptible. The HWA came from Asia without any of the natural enemies that keep populations in check in its native range. HWA was first reported in the eastern US in Virginia in the mid 1950's. Since then, it has spread north to Connecticut and south through North Carolina. It reached eastern Tennessee in 2002, and was first reported in eastern Kentucky in spring 2006. Systemic insecticides containing the active ingredient imidacloprid can be used as soil drenches or injections to control the HWA.

There are multiple ways that plants in urban landscapes can contain imidacloprid-contaminated nectar, since it is commonly applied in the landscape for many pests and many greenhouse plants are treated with prior to sale and transplanting. Imidacloprid may persist in nectar for a long time, since soil applications were effective against foliar pests for 1 to 2 years in containers and landscape trees. Injections of concentrated volumes of imidacloprid applied to trees trunks and roots were effective for 12 months for ash and linden. A soil application of imidacloprid to Eucalyptus tree resulted in 500 ppb in nectar and pollen, which will kill any insect feeding on nectar and pollen. Tree injections of imidacloprid at flowering are cause for concern, since linden flowers are a good source of nectar and pollen for bees, butterflies, and other beneficial insects.

Nearly all shade trees and many shrubs are subject to borer attack, the tunneling of immature beetle or moth larvae through the cambium, sapwood or heartwood of the host plant. The emerald ash borer is now one of the most destructive non-native insects in the United States. The potential damage of this insect rivals that of Chestnut blight and Dutch Elm Disease. Since its accidental introduction into the United States and Canada in the 1990s, and its subsequent detection in 2002, it has spread to 14 states and adjacent parts of Canada. It has killed at least 50 to 100 million ash trees so far and threatens to kill most of the 7.5 billion ash trees throughout North America. Traditionally, borers have been treated with a trunk spray application of insecticide that kills the newly hatched insects before they tunnel into the plant. However, imidacloprid, a systemic insecticide that is applied as a soil drench around the base of target plants, is making borer control easier and targeting the small larva as they chew their way into the plant. It has a twelve-month residual effect. The chemical is absorbed by the plant's root system and moved throughout it's trunk, branches and foliage.

Soil injections of imidacloprid are effective at preventing attack by the walnut twig beetle, a very aggressive beetle that will attack both healthy and stressed trees. Imidacloprid can also be injected directly into the trunk or soil so there is no public contact. Soil injections of imidacloprid are also very effective against Elm leaf beetles, a cyclic pest, European elm scale, one of the most widespread and destructive scale insects, Hawthorn mealybug and Kermes scale, which affects pin oak and red oak trees.

Viele Ackerkulturen werden heute von der Aussaat bis zur Ernte mit Pestiziden behandelt. Pestizide beeinträchtigen ganz erheblich die biologische Vielfalt. Neben bestimmten – für den Anbau schädlichen – Pflanzen und Insekten eliminieren viele Pestizide auch alle übrigen Wildkräuter und Insekten – und fehlen höheren Tieren dann als Nahrung. Etliche Arten der Feldvögel haben daher in den letzten Jahren radikal abgenommen. So wird die Stoffgruppe der Neonikotinoide für das Bienen- und das Vogelsterben in der Agrarlandschaft verantwortlich gemacht.

Anthropogenic habitat loss is usually cited as the most important cause of recent species’ extinctions. We statistically compared areas in Canada where imperiled species currently occur, versus areas where they have been lost. Using multiple regressions, we relate the numbers of species that had suffered range reductions in an ecoregion to variables that represent present habitat loss, pesticide use and human population density. We find high losses of imperiled species in regions with high proportions of agricultural land cover. However, losses of imperiled species are significantly more strongly related to the proportion of the region treated with agricultural pesticides. The relationship between species losses and area treated with pesticides remains significant after controlling for area in agriculture. Our results are consistent with the hypothesis that agricultural pesticide use has contributed significantly to the decline of imperiled species in Canada. Habitat conversion per se may be a less important cause of species declines than how that converted habitat is used.