This is the third part of a series on winter tree insects. This article examines brown marmorated stink bug and Douglas-fir beetle.
Introduction
Through the winter months, plants conserve their energy, often enduring inclement weather in anticipation of spring. Due to the frigid temperatures, many insects enter a state of dormancy, overwintering on or within their hosts. While some insects are visible during winter, others conceal themselves in bark crevices or beneath the soil surface. The following examines some of the most common insects to infest trees during winter, and how they may be observed.
Brown Marmorated Stink Bug (Halyomorpha halys)
Brown marmorated stink bug, often abbreviated to BMSB, and sometimes referred to as a stink bug, is a true bug in the family Pentatomidae. Brown marmorated stink bug is an invasive polyphagous insect that infests various fruits, vegetables, ornamental plants, and farm crops. The insect is indigenous to Asia, where it is recognized as a significant agricultural pest.
Brown marmorated stink bug was introduced to North America from China or Japan. It has since become abundant throughout the United States. It is particularly common in the Mid-Atlantic and Northeast regions, where it frequently infests orchards and ornamental plants.
Hosts
Brown marmorated stink bug infests a bevy of plants. It frequently attacks apples, blackberries, citrus fruits, field corn, sweet corn, figs, green peppers, mulberries, peaches, persimmons, and tomatoes, as well as a multitude of beans. Infestations are also common on weeds, and many ornamental plants, particularly fruit trees.
Symptoms of Infestation
Brown marmorated stink bug causes widespread damage to fruits, vegetables, and plant foliage. The adults and nymphs use their proboscis to pierce the leaves of host plants, and consume their fluids. As they feed, the insects inject saliva into the plant. The saliva is toxic to many plants. On fruit, the persistent feeding of the insects can result in a type of distortion called cat facing, in which the fruit develops necrotic brown spots along its surface, rendering it unsuitable for consumption. This type of deformation is common on peaches. Infested apples often exhibit pitting and discoloration symptoms, as well as extensive scarring where necrotic spots have formed.
On ornamental plants, the feeding of the nymphs and adults promotes leaf stippling, which inhibits plant growth. It can also promote the degradation of plant seeds. Fruit trees will often experience a significant reduction in fruit yield. Plants that have been weakened by brown marmorated stink bug may be more easily invaded by disease pathogens, and other insects.
Management
- Inspect windows, doors, siding, utility pipes, chimneys, and other openings for splits or fractures. If any damage is present, seal or repair the openings to reduce the number of overwintering sites available to the adults. Damaged screens on doors and windows should be maintained or replaced.
- In external areas, insecticidal applications can provide some minor control for the adults. Applications should be performed in fall before the adults overwinter. Avoid using insecticides in buildings. While insecticidal treatments are effective at moderating BMSB populations, the husks of the insects may attract carpet beetles, which will readily devour dry goods and other natural products in households.
- Brown marmorated stink bug can be removed from interior areas with the assistance of a vacuum cleaner.
- Brown marmorated stink bug has several natural predators that help to limit its populations. Parasitic wasps and birds are two of the most common predators in the insect’s native range. Trissolcus halymorphae, an egg parasitoid, has been identified as a natural control agent of BMSB. When present, Trissolcus halymorphae can encourage a rapid collapse of BMSB populations.
Douglas-fir Beetle (Dendroctotonus pseudotsugae)
Douglas-fir beetle is a bark beetle that infests Douglas-fir. It is one of the most destructive pests of Douglas-fir. Outbreaks of Douglas-fir beetle can persist for several years. When populations are dense, Douglas-fir beetle can decimate forests and stands, rapidly killing hundreds to thousands of Douglas-firs.
Hosts
Douglas-fir beetle primarily infests Douglas-fir. Western lerch is occasionally infested, albeit with less frequency. The beetle is generally attracted to trees that have been weakened by environmental stressors, disease, or other infestations. Trees that have suffered fire scorch or have been felled are more prone to infestation.
Symptoms of Infestation
As the adults and larvae bore through the phloem, they produce a reddish-brown dust, which can be found in bark crevices and exit holes on the lower portion of the tree, or on the ground at the base of the tree. Clear resin may be exuded from the upper portion of infested trees. The resin is conspicuous, and may be visible from afar. Removing sections of the bark will reveal the egg galleries, eggs, and larvae. Infested trees will exhibit needle discoloration. The needles will transition from green to yellow, before deepening to orange, and then finally, a reddish-brown. Needle discoloration will not become apparent until several months to a year following the initial infestation. During years when conditions are dry, needle discoloration may be hastened. Woodpeckers will often create holes in infested trees while attempting to extract the larvae.
Management
- When planting, select trees that are immune to infestation from Douglas-fir beetle.
- Maintain trees through sound cultural practices. Ensure that trees are sufficiently watered, especially during extended periods of drought. Each year, apply a layer of organic mulch around the base of susceptible trees. This will help to improve the soil quality, moderate the soil temperature, and retain soil moisture.
- Cull severely weakened trees to provide some natural control to infested areas.
- Anti-aggregation pheremone packets containing Methylcyclohexanone can be hung on vulnerable trees. The packets will disrupt beetle aggregation, and limit population growth.
- Registered insecticides can be applied to trees to combat infestations. Applications should be performed in spring, as the larvae and adults emerge.
- Cold, dry winters can kill overwintering broods.
- Several parasites and predators feed on Douglas-fir beetle. A Braconid wasp parasitizes the larvae. Many Dolicopdid flies prey on the larvae, while Clerid beetles consume the larvae and adults. Woodpeckers feast on the larvae, and will often convene around infested trees.
