Photo: Joseph Berger, Bugwood.org
Biological control entails periodic releases of biological control agents or natural enemies including parasitoids and predators to regulate or maintain insect or mite pest populations below damaging levels. Two common insect pests encountered in greenhouse production systems are fungus gnats, Bradysia spp., and western flower thrips, Frankliniella occidentalis. There are biological control agents commercially available for both insect pests. For fungus gnats, there is the soil-inhabiting predatory mite, Stratiolaelaps scimitus (formerly ‘Hypoaspis miles’ ); and for western flower thrips, there are the predatory mites, Neoseiulus (formerly Amblyseius) cucumeris and Amblyseius swirskii. However, two generalist predators also commercially available for use in greenhouse production systems that prey upon fungus gnats and western flower thrips are the rove beetle, Dalotia (formerly Atheta) coriaria, and the insidious flower bug, Orius insidiosus.
Dalotia coriaria adults are approximately 3 to 4 mm in length, glossy, dark brown and covered with a thick pubescence (Fig. 1). Although adults are mobile and can fly, which allows them to disperse within a greenhouse away from the original release site, they tend to spend most of their time in growing media. Larvae are white in the early instars, whereas later instars are yellow-brown. Development time from egg to adult takes approximately 17 days; however, development time varies depending on temperature. For example, development time from egg to adult is 21 to 22 days at 77º F (25º C), and 11 to 12 days at 86º F (30º C). Adult longevity can influence effectiveness because adults prey and lay eggs over an extended period of time, which can enhance regulation of fungus gnat larval populations in greenhouses. Dalotia coriaria is easy to rear under laboratory conditions using live prey (fungus gnat larvae) or artificial diets including ground trout pellets, turkey starter crumbs and/or oats. Greenhouse producers in the United Kingdom are experimenting with “breeding boxes” or “rearing-release boxes” to establish rove beetle populations in poinsettia and cyclamen crops. However, cannibalism can occur among rove beetle adults and larvae when rearing conditions become crowded.
Rove beetle adults and larvae reside in growing medium feeding on fungus gnat larvae. Studies in our laboratory at Kansas State University have shown that consumption of fungus gnat larvae by rove beetle adults increases as the number of rove beetle adults increases with a maximum of four rove beetle adults per 4.0-inch container. Dalotia coriaria is a generalist predator and feeds on a number of different insect pests that have life stages located in the growing medium. In addition to feeding on fungus gnat larvae, D. coriaria will feed on the eggs and first instar of the European pepper moth, Duponchelia fovealis. The ability of rove beetle adults to effectively regulate fungus gnat larval populations can be influenced by cultural practices, such as growing medium type and watering practices. Throughout the United States, greenhouse producers are successfully using D. coriaria against fungus gnats. Recent research in our laboratory at Kansas State University has demonstrated that rove beetle adults will also feed on the pupal (prepupae and pupae) stages of the western flower thrips in the growing medium. Consequently, this provides a means of dealing with a life stage that is not affected by most insecticides.
Insidious flower bug
Orius insidiosus adults are 2 to 5 mm long, black, and flattened with black and white wings (Fig. 2). Eggs are laid inside plant tissues with light-brown nymphs emerging later on. Plant suitability may affect egg-laying by females; a factor mainly associated with plant nutritional quality. Female longevity is about 26 days under laboratory conditions. The insidious flower bug is a predatory bug widely used to regulate pest populations in greenhouse production systems affiliated with vegetables and ornamentals, and is relatively easy to mass produce. The insidious flower bug is a generalist predator with the nymphs and adults feeding on a wide range of insect and mite pests including: aphids, spider mites, thrips and whiteflies (Fig. 3). The insidious flower bug can regulate western flower thrips and twospotted spider mite, Tetranychus urticae, populations when both pests are present simultaneously. In addition, O. insidiosus will feed on plant sap and pollen in the absence of prey. The insidious flower bug feeds on the larvae and adult stages of western flower thrips located on plant leaves and flowers, and can consume >20 western flower thrips per day. A benefit of releasing the insidious flower bug instead of predatory mites (N. cucumeris or A. swirskii) is that nymphs and adults of O. insidiosus feed on the larvae and adults of western flower thrips, whereas the predatory mites only feed on the first instar larvae of western flower thrips.
In winter in the northern portions of the United States, the insidious flower bug undergoes reproductive diapause in response to short days (<12 hours per day); consequently, this can affect the capacity of the predatory bug to effectively regulate western flower thrip populations from September through March. However, extending the daylength (=12 hours of light per day) can inhibit the insidious flower bug from entering diapause. Banker plant systems consisting of non-crop plants that provide alternative food sources or prey for predators, as well as pollen and nectar, can help enhance establishment of insidious flower bug populations. ‘Black Pearl’ pepper, Capsicum annuum, plants provide sufficient pollen that increases development, fitness and abundance of insidious flower bug adults. However, the highest population growth of insidious flower bug occurs on ‘Purple Flash’ pepper plants, which may be a more suitable banker plant for use in greenhouse production systems by providing food for the insidious flower bug in the absence of western flower thrips. The use of banker plants may increase the effectiveness of O. insidiosus in regulating western flower thrips populations.
Two generalist predators also commercially available for use in greenhouse production systems that prey upon fungus gnats and western flower thrips are the rove beetle, Dalotia (formerly Atheta) coriaria, and the insidious flower bug, Orius insidiosus.
Plant type may impact the ability of the predatory bug to provide sufficient regulation of pest populations. For instance, O. insidiosus does not sufficiently establish on tomato, Solanum lycopersicum, plants, resulting in minimal regulation of western flower thrips populations.
Dalotia coriaria and O. insidiosus are commercially available generalist predators that, when released early in a cropping cycle, can be effective in regulating fungus gnat and western flower thrips populations. Therefore, greenhouse producers should consider using these natural enemies in greenhouse production systems.