The click beetle, an insect known for its elongated, flattened body and the distinctive audible snap it makes, is a common sight in gardens and fields across the world. This unique clicking sound and sudden flip into the air is a defense mechanism used to startle predators or right itself when turned on its back. While the adult beetles are largely harmless, their presence often raises concern among gardeners and farmers regarding their potential for destruction or classification as a pest.
Native or Invasive
The question of whether click beetles are classified as an invasive species is often misunderstood, as many problematic garden insects are native to the area. Of the thousands of click beetle species worldwide, nearly a thousand are native to North America alone. These native species are not considered invasive, which is a term reserved for non-native organisms that cause significant economic or environmental harm in a new habitat. While certain species of their larvae can become agricultural pests, this makes them a native pest, not an invasive one. A native pest is an organism that is naturally occurring but whose population has grown to damaging levels, often due to changes in farming practices or habitat.
Identifying the Life Stages
The life cycle of the click beetle is characterized by four distinct stages: egg, larva, pupa, and adult, with the larval stage being the source of almost all plant damage. Adult click beetles are generally slender, brown to black, and range in size from one-quarter to over one inch long, depending on the species. The adults are mostly nocturnal and often feed on nectar, pollen, or sometimes smaller insects, rarely causing harm to established plants.
The problem stage is the larva, commonly known as the wireworm, which is a slender, cylindrical, and hard-bodied grub. Wireworms are typically yellowish-brown and can grow up to an inch or more in length, with three pairs of tiny legs located directly behind their dark head capsule. The larval stage is notably long, with most wireworm species living in the soil and feeding on plant material for a period that can last from two to six years before they finally pupate.
The Damage Caused by Wireworms
Wireworms are destructive soil-dwelling pests that feed on the underground parts of plants for several years. Their initial damage often targets seeds, boring into them before they have a chance to germinate, which results in poor crop stand establishment. Young seedlings are also susceptible, as wireworms feed on the roots and bore into the base of the stem, causing the plant to wilt and die.
The most reported damage occurs with root and tuber crops, such as potatoes, carrots, onions, and beets, where the larvae bore tunnels into the flesh. These small, clean-edged holes destroy the marketability of the harvest. Wireworms are particularly problematic in fields that were recently converted from sod or pasture, as the larvae thrive in the extensive root systems of grasses. They prefer moist soil conditions, with damage often more pronounced in low-lying or frequently irrigated areas.
Effective Management Strategies
Managing wireworm populations effectively requires a long-term approach that focuses on disrupting their extended life cycle in the soil. Cultural controls are often the first line of defense, including implementing crop rotation that avoids planting susceptible crops after grasses or small grains that favor wireworm development. Incorporating crops like mustard or buckwheat into the rotation can also help suppress wireworm numbers due to their biofumigant properties.
Physical methods can be employed to reduce localized populations, such as tilling the soil during warm, dry periods to expose the larvae to predators and desiccation. Trapping is also useful for monitoring and reduction, which involves burying small pieces of potato or carrot as bait to attract the wireworms. For severe infestations, biological treatments like certain species of beneficial nematodes, such as Heterorhabditis bacteriophora, can be watered into the soil to target the larvae.