The lady beetle Stethorus punctillum has an unusual ability to find small infestations of twospotted spider mite in the field. Could it do the same in greenhouse cultures of tomato, pepper and cucumber?
Researchers in Canada decided to develop a mass-rearing technique for the beetle and release it in greenhouses early in the season to reduce the probability of spider mite outbreaks.
Batches of 400 beetles were released in tomato, pepper and cucumber greenhouse in the Fraser Valley (B.C., Canada) during February and March 1997, and the houses were monitored for establishment and movement.
S. punctillum established on pepper and cucumber but not tomato, corroborating other observations that the larvae cannot survive on tomato. Stethorus is a highly mobile predator. Within minutes of release beetles were observed searching for mites on plants near the release area and many flew to neighboring plants. At a pepper house, Stethorus was observed over 400 feet from the release site after 12 days. Survival during shipping was about 94%; of the beetles designated for release, about 94% moved into the greenhouses by the following day-the remainder were dead. About 70% of females (half of all the beetles) with adequate food laid eggs during the 5-day period following receipt from the rearing facility. Each female laid 1.5 eggs per day on average and egg hatch was nearly 100%. This was lower than the expected 4 eggs per female per day; food availability may explain the difference.
Given the small Stethorus releases, mite control in the greenhouses was generally a function of the greenhouse biocontrol program which utilized the predatory mite Phytoseiulus persimilis and other predators. However, at a cucumber house, Stethorus cycled through the season, and in combination with P. persimilis regulated mite populations at acceptable levels.
This work suggests that early spring releases of S. punctillum have potential for mite control on greenhouse pepper, and especially cucumber. Commercialization of S. punctillum is being investigated.
Raworth, D. A., J. Whistlecraft and D. Gillespie. 1998. A lady beetle for mite control. Pest Management News 9(4): 11 (Winter 1997/1998).
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