Insecticides

Between 1985 and 2005, at least 25 exotic species of wood borers were found to have become established in the United States. Due to the lack of both natural enemies and coevolved tree-resistance mechanisms to control these borers, these exotic species may become destructive and uncontrollable invasive tree pests. One example is the European woodwasp, Sirex noctilio (Hymenoptera: Siricidae), which has become a serious pest in each country to which it has been introduced. Another example is the emerald ash borer, Agrilus planipennis (Coleoptera: Buprestidae), discovered in North America in 2002. Methods to control or eradicate wood-boring insects are still being developed, but the newest methods usually involve application of systemic insecticides, such as imidacloprid through direct trunk injection, soil injection, or soil drench. This chemical moves within trees to reach cryptic larvae as well as affecting adults of some species that feed externally. The desired level of control, however, is seldom achieved by this approach due to unpredictable translocation of insecticides within trees and asynchronous larval development, both of which allow many insects to evade treatment. Moreover, chemical insecticides are usually broadly toxic, resulting in risks to non-target organisms and potential groundwater contamination. Many chemical insecticides and formulations require handling by licensed applicators resulting in prohibitive costs.

The Asian longhorned beetle’s (ALB) recent introduction to the United States is a serious threat to hardwood trees. This beetle has no known natural predator in the United States and the potential to cause more damage than Dutch elm disease, chestnut blight, and gypsy moths combined, destroying millions of acres of America’s treasured hardwoods, including national forests and backyard trees. Recently the insecticide Imidacloprid has presented good results in field applications and is increasingly being used in conjunction with other methods to protect trees and eradicate the pest. The citrus longhorned beetle (CLB), a very close relative of ALB, is a severe pest of citrus, but it also attacks most of the same tree species attacked by ALB. Unlike ALB, however, CLB typically attacks its host in the lower 0.5 metres of the trunk, around the root collar and on exposed roots. Therefore, CLB quickly girdles and kills its hosts. While CLB is also native to Asia (e.g. China, Japan), it has been intercepted twice in the USA (once on bonsai) and in a number of locations in Europe. More alarming are the new CLB infestations found in the Netherlands in 2007 and in Germany in 2008. Furthermore, the first CLB infestation found in Europe, specifically in northern Italy, has continued to expand in the past few years.

The large pine weevil, Hylobius abietis, is the most important pest of replanted coniferous sites in Ireland and throughout northern Europe. If left unchecked, it can kill every young tree on a site. the normal method to control weevils is to use chemicals, but another approach being developed uses more natural methods. Pine weevil is the only forest pest against which chemical insecticide is routinely applied in Ireland and there is a real need to develop an ecologically sustainable management strategy for it. The weevils develop in the stumps of recently cut conifers and emerge as adults which attack newly planted trees, both conifer and broadleaf. Weevils feeding on the bark can kill a young tree within days. The traditional approach is to treat each seedling with insecticide.

The invasive red palm weevil, Rhynchophorus ferrugineus (Olivier), has become the major pest of palms in the Mediterranean Basin. Chemical control against this species is difficult because of its cryptic habits and is mainly based on the repeated application of large quantities of synthetic insecticides. The aim of this work has been to evaluate in the field the efficacy of imidacloprid (Confidor® 240 OD) and Steinernema carpocapsae Weiser with chitosan (Biorend R® Palmeras) as soil and stipe treatments respectively, alone or in combination, against this pest. All treatments significantly reduced the mean number of immature stages of R. ferrugineus per palm. However, there were no significant differences among the different treatments considered. Efficacies ranged from 83.8 to 99.7% for the mean number of immature stages found in the palms and resulted in a significant increase in palm survival compared with the untreated control (75.0–90.0% versus 16.5% respectively). Both imidacloprid and S. carpocapsae in a chitosan formulation proved highly effective against R. ferrugineus in the field, and their efficacies did not significantly change when used in combination.

Loblolly pine (Pinus taeda L.) covers 16 million ha of forestland in the southeastern United States, more than half of which consists of plantations. Regeneration pests of loblolly pine (Pinus taeda L.) threaten growth and survival in intensively managed loblolly pine plantations throughout the southeastern United States. The Nantucket pine tip moth, Rhyacionia frustrana (Comstock), in particular, often reduces growth of loblolly pine but has been difficult to control with traditional insecticides due to multiple annual generations and multi-year infestations which are difficult to predict in timing and location. Relatively new systemic insecticide products offer a solution in that their efficacy persists through multiple generations and years after a single application. Efficacy of systemic imidacloprid and fipronil were evaluated side by side across multiple sites in Virginia. Significant reductions in Nantucket pine tip moth damage were noted in trees treated with either the imidacloprid or fipronil product compared with check trees. After 2 yr, growth improvement of treated trees relative to controls was modest and not signiÞcant at all sites, but per acre volume indices were significantly greater in treated blocks as a result of higher tree survival. Reduced seedling mortality was attributed primarily to prevention of damage by pales weevil, Hylobius pales Herbst (Coleoptera: Curculionidae), by both insecticide treatments. Control of pales weevil in addition to pine tip moth suggests that systemic insecticide products with a long window of efficacy might control additional nontargeted pests.

Imidacloprid, developed by Bayer CropScience in 1985, is an insecticide, a seed treatment insecticide and seed treatment insecticide/fungicide combination. Bayer still holds patents on the active for some formulations, specifically when combined with fertilizer. Its mode of action is nicotine acetylcholine receptor agonist/antagonist, and it is registered in more than 100 countries worldwide for use on more than 140 crops. It is used primarily on canola, cereals, corn, cotton, oil seed rape, pastures, potatoes, rice, sorghum, sugarbeet and sunflowers for approved control of aphids, fruit flies, leafhoppers, grubs, termites, thrips, white fly, wireworms, various beetles (including flea beetle and pygmy beetle), various weevils, nematodes and various fungal diseases. It also has widespread applications in noncrop, including nursery, landscape, forestry, pest control and veterinary applications. Bayer Animal Health has been using a 10% imidacloprid formulation for its popular Advantage/Advantix flea treatments for dogs and cats as early as 1986.

Many kinds of lace bugs, family Tingidae, feed on landscape plants throughout the United States. Hosts include alder, ash, avocado, azalea, coyote bush, birch, ceanothus, fruit trees, photinia, poplar, sycamore, toyon, walnut, and willow. Several dozen species of lace bugs occur in the western United States, mostly on trees and woody shrubs. California Christmas berry tingid (Corythucha incurvata), ceanothus tingid (Corythucha obliqua), Western sycamore lace bug (Corythucha confraterna), and the recently introduced avocado lace bug (Pseudacysta perseae) are some of the species that can be pests. Almost any insecticide will control lace bugs if it is sprayed directly onto the insects. Insecticides that are absorbed and move within plants can provide longer-lasting control than contact sprays. Imidacloprid is available to both homeowners and professional applicators. In situations where IPM-compatible insecticides are inadequate, imidacloprid is usually the preferred choice. It may provide season-long control if applied in spring before populations dramatically increase. Imidacloprid can be applied as a foliar spray or soil drench. It can be injected directly into trunks if their diameter is relatively large.