BENEFICIAL BUG SPOTLIGHT
Carabid Beetles-generalist predators of many early-season pests
Overwintering carabid beetles have emerged and begun hunting in fields throughout the Delmarva region. These predatory ground beetles are active hunters capable of consuming their body weight in pests each day. At night, they can be seen quickly roaming fields in search of prey, particularly in wetter areas and those with greater amounts of residual crop debris. Carabid beetles are typically active from early spring through autumn and are known early-season predators of aphids, slugs, and immature stages of seedcorn maggots and other fly pests. Adult beetles hunt primarily by searching along the soil surface, but some species, commonly known as caterpillar hunters, will climb into the foliage in search of food. Larval stage carabid beetles are also predatory, feeding primarily on other insect larvae below the soil surface. Additionally, many carabid species will also feed on weed seeds along the soil surface, helping reduce total weed emergence and biomass. Some studies have estimated that a community of ground beetles may consume up to 1000 seeds/m2 per day, and that seed consumption by carabids could help reduce the total stock of a weed seed species on the soil surface by 65-90%.
Carabid beetles have four distinct life stages: egg, larva, pupa, and adult. Egg, larval, and pupal stages are spent primarily underground and are rarely seen. Adult carabids vary in appearance depending on species. They range in size from 1/8 to 1½ inches long with a plain dark coloration (Figure 1A). However, some can be iridescent green, bronze, or blue in color (Figure 1B, 1C). Carabid beetles usually produce only one generation per year, but adult beetles can live up to 3 years by overwintering under plant debris.
Carabids can be found in virtually all agronomic and vegetable cropping systems, as well as orchards, brambles, along field edges, and in vegetation along drainage ditches. In general, reduced tillage fields will have higher levels of ground predator activity than tilled fields. Though they will not fully control most pests when pressure is high, carabid beetles can help improve insect pest control while simultaneously reducing weed pressure, making them valuable contributors to sustainable agriculture.
This article is featured in the Vegetable and Fruit News, Vol. 16, Issue 1.