Efforts to reduce reliance on chemical controls in cut flower production have focused on using predatory mites and bugs for western flower thrips control. However, biological control alone has not succeeded in reducing thrips populations to acceptable levels. Two commercial formulations of the fungus Beauveria bassiana were tested for their ability to control western flower thrips.
In laboratory trials and caged rose trials, B. bassiana sprays killed up to 82% of the thrips on rose foliage, depending on the concentration of the spore preparation, at 79°F and 75% relative humidity. Humidity is an important factor influencing the degree of thrips control, with greater mortality with increasing humidity. Even in greenhouses where relative humidities vary between 50 and 100% within a 24-hour period, the two formulations of B. bassiana tested should significantly reduce thrips numbers. Overall population reductions were variable, ranging from 50 to 97%.
Similar results were seen in commercial plantings of roses and carnations, with thrips populations reduced to very low levels, generally within growers' tolerable range.
There were differences in performance between the two formulations tested. The oil formulation reduced thrips numbers within the first week, while the wettable powder required up to 2 weeks. Both formulations could be used to help control western flower thrips in greenhouse flowers, although the emulsifiable oil formulation works more quickly.
Because the fungal pathogen kills the thrips more slowly than insecticides it must be applied earlier in the appearance of western flower thrips to maintain the population at low levels. Also, if lots of thrips immigrate into a greenhouse, fungal infection may not be able to keep up with the influx and the thrips may not be killed fast enough to prevent damage. Finally, because spores kill insects through direct contact, good coverage is essential to achieve adequate control.
Murphy, B. C., R. A. Morisawa, J. P. Newman, S. A. Tjosvold, and M. P. Parrella. Fungal pathogen controls thrips in greenhouse flowers. Calif. Agric. 52(3): 32-36.
Biological Control of Citrus Mealybug in an Indoor Shopping Mall
The wasp parasitoid Leptomastix dactylopii has successfully controlled citrus mealybug in agricultural and greenhouse environments, but little is known about its effectiveness in interior plantscapes. A study was conducted at a large indoor shopping mall in Fort Worth, Texas where mealybugs were a problem.
A single release of about 200 wasps was made into each of five moderately- to heavily-infested ficus trees. Five months after the release, the percentage of infested leaf tips had declined from 100% to 18% and foliage appearance had improve significantly. Adult parasitoids were observed eight months after the release, but mealybug infestation had increased once again. However, nearly all the mealybugs at this time were still too young to be attacked by the parasitoid. This suggests that control may be cyclical or that periodic releases may be needed to maintain low mealybug populations.
The wasps moved away from the initial release sites, with both adult parasitoids and parasitized mealybugs observed in other areas of the mall as much as 300 feet from the nearest release site.
This wasp seems to be compatible with office, retail and food service activities because of its small size and tendency to remain close to the foliage. At current prices of 14 cents per parasite, use of this wasp compares favorably with the cost of chemical controls, particularly if the wasps continue to reproduce and suppress infestation for months or years without additional releases.
Merchant, M. and J. Hoelscher-Cox. 1998. Biological control of citrus mealybug in an indoor shopping mall. In Knutson, A. and J. Smith, eds. Biological Control Program 1996-1997 Report, Texas A&M University, Department of Entomology, pp. 17-18.
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