Small mites of the family Eriophyidae and Tarsonemidae cause major problems in various crops. The tomato russet mite, Aculops lycospersici, can be very problematic in tomatoes. Other harmful mites of this family are the dry bulb mite, Aceria tulipae, which causes problems during the storage of tulips, and the redberry mite Acalitus essigi, which damages the fruits in blackberry. In amaryllis, it concerns the bulb scale mite, Stenotarsonemus laticeps, in bromeliads, the pineapple tarsonemid mite, Stenotarsonemus bananas, and in gerbera, it is often a mix of Tarsonemus violae and the broad mite Polyphagotarsonemus latus.
Although the crops where these mites cause problems are completely different, they all have in common that the mites are very difficult to control due to their extremely small dimensions. Predatory mites are, in principle, effective predators, but they cannot get to the places where these small mites are hiding.
Entomologists from Wageningen University & Research have investigated new natural enemies for the control of small mites in a top sector project. During this research, the tiny gall midge Trisopsis tyroglyphi was discovered, whose larvae proved to be good predators of both eriophyid and tarsonemid mites. The species was for the first time found in the Netherlands. The larvae can develop very well on the storage mite Tyrophagous putrescentiae. It was striking that juvenile development was particularly slow at 15 degrees (>80 days). At 25 degrees, the life cycle is relatively short, on average 23 days. The midge adults are very fragile and live only for four days.
The application of these predatory midges as biological control agents is very crop-dependent. In amaryllis, they were found deep in the bulb where they preyed on bulb scale mites, but in practice, they failed to establish. In bromeliads, under humid and warm conditions, the predatory midge was found to settle surprisingly well in flowers. However, the contribution to the control of the pineapple tarsonemid mite has not yet been demonstrated. A trial with gerbera showed that the predatory midges could contribute to the control of the broad mite, but complete control was not achieved.
The best results were achieved on garlic. There the dry bulb mite was reduced by more than 80% in treatments with the predatory midge, but this was only achieved when supplemented with the prey mite T. putrescentiae. We believe that this new predatory midge could be an interesting new control agent for tarsonemid and eriophyid mites in tulip, begonia, and possibly gerbera. The predatory midges are easy and relatively cheap to rear on storage mites, and a license has been granted for use in practice.
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Wageningen University & Research