Nursery, Greenhouse, and Landscape News
Ambysieus hibisci and A. degenerans:
Two "New" Predacious Mites With Potential for
Biological Control of Western Flower Thrips
Western flower thrips (Frankliniella occidentalis) is one of the most destructive insect
pests of greenhouse crops, primarily because of its ability to destroy flowers and transmit tomato
spotted wilt virus and impatiens necrotic spot virus. Resistance to many insecticides and the poor
performance of new systemic insecticides, such as imidacloprid, has growers seeking
alternatives. Anthocorid bugs and phytoseiid mites are the natural enemies most commonly used.
Effectiveness of predatory mites is limited by their tendency to enter diapause under short days
in winter, and by the susceptibility of mite eggs to desiccation during the dry conditions that
occur in winter and mid-summer. Five subtropical mites (Amblyseius hibisci, A. degenerans, A.
limonicus, A. scutalis, and A. tularensis) have recently been evaluated along with two other
species (A. cucumeris and A. barkeri) that are commonly sold to growers for thrips management
for their potential as biological control agents in greenhouses.
A series of laboratory studies examined predation and oviposition rates, diapause, and
egg susceptibility to low humidity. A. degenerans, and A. hibisci were the best possible
biological control agents for western flower thrips in greenhouses under short-day length and
low humidity. These species did not enter diapause and were the least sensitive to egg
desiccation under low humidity. Rates of predation and oviposition for these two species were
lower than for A. cucumeris, but greater than for the other species. A. limonicus demonstrated the
highest predation and oviposition rates of all species and did not enter into diapause. However,
its eggs were highly susceptible to low humidity conditions. These promising new mites have yet
to be tested in the greenhouse.
- Summarized by Ray Cloyd and Cliff Sadof
van Houten, Y. M., P. C. J. van Rijn, L. K. Tanigoshi, P. van Stratum, & J. Bruin. 1995. Preselection of
predatory mites to improve year-round biological control of western flower thrips in greenhouse crops.
Entomologia Experimentalis et Applicata 74: 225-234.
Convergent Lady Beetle Releases for Aphid Control on Potted Plants
Historically, releases of convergent lady beetle have not been recommended because
aggregation-collected beetles generally disperse soon after release and were believed ineffective.
For inoculative control (where the offspring of the released individuals are supposed to provide
control) this is probably true. However, recent studies have shown that convergent lady beetles
can provide inundative control despite their propensity for dispersal.
Most aggregation-collected beetles dispersed from aphid-infested potted chrysanthemum
plants within 1 to 3 days of release. Beetles that were allowed to drink and fly in a screen tent
for 7 to 10 days before release, and insectary-reared beetles, stuck around the potted plants a little
longer. Even though the beetles dispersed within days, they significantly reduced the aphid
populations before they left. Each beetle in these trials ate 25 to 170 melon aphids per day,
consuming more when released on plants with higher aphid densities.
Although preconditioning delayed dispersal, it didn't have much effect on aphid control,
since both the collected and "flown" beetles controlled the relatively high aphid populations
present. Control might differ at lower aphid densities more characteristic of a commercial
nursery, and the host plant, aphid species and environmental conditions may also affect aphid
control from beetle releases.
Dreistadt, S. H. and M. L. Flint. 1996. Melon aphid (Homoptera: Aphididae) control by inundative
convergent lady beetle (Coleoptera: Coccinellidae) release on chrysanthemum. Environ. Entomol. 25: 688-697.
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