Nursery, Greenhouse, and Landscape News

Searching for Natural Enemies of Bulb Mites

The tiny bulb mite feeds on the underground portion of bulbs and is very difficult to control. No parasitioids or pathogens of this mite are known and few predators are available to combat it.

The Netherlands, Taiwan and Japan are some of the countries where the bulb mite is an established pest that were explored for suitable candidates for biological control on lilies. Mesostigmatid mites were the predominant predator found in assocation with the bulb mite in these areas. The most abundant species were Hypoaspis aculeifer, Lasioseius bispinosus and Parasitus fimetorum. These predators appear to feed and reproduce on a diet of exclusively bulb mite.

These predatory mites were able to control the bulb mite in small-scale population experiments on lily. Under laboratory conditions simulating propagation (lily scales mixed with vermiculite and stored at 23C and > 90% RH) the laelapid mite, H. aculeifer, was the most effective predator. The ascid predator, L. bispinosus, was much less effective, but being relatively small and being successful in attacking the juvenile stages of the bulb mite it may be better able to search for bulb mites hidden inside the lily bulb. The parasitid predator, P. fimetorum, failed to control the bulb mite when vermiculite was used as a medium, but turned out to suppress this prey when peat was used instead.

Various strains of H. aculeifer were collected that varied in their ability to control bulb mites. Two Dutch strains and a Taiwanese strain were compared with a German strain that was not collected from lily bulbs, but from agricultural areas near Bremen. In addition, a Canadian strain of a related species (Hypoaspis miles), known to control sciarid fly larvae, was also tested. H. miles died out without noticeable impact on the bulb mite population, whereas all strains of H. aculeifer were able to suppress the bulb mites to very low numbers, although those collected in association with the pest were superior to the German strain.

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