Weekly pollen optimises control of the tomato russet mite by Pronematus ubiquitous

The tomato russet mite, Aculops lycopersici (Massee), is a challenging eriophyid pest which currently lacks a biological control solution. Recently, the predatory mite Pronematus ubiquitus (McGregor) has shown the potential to prevent outbreaks of A. lycopersici. However, to ensure a stable predation rate throughout the season, an alternative food supply needs to be optimised.
We assessed the effect of different pollen supply frequencies on the populations of P. ubiquitus and its predation on A. lycopersici. A semi-field replicated experiment was conducted in a greenhouse. Tomato plants were planted in insect-proof cages. The predator was released six weeks before the infestation of the pest mite. Pollen of Typha angustifolia L. was supplied each week, once every fortnight and once every three weeks. The number of predatory and pest mites was assessed by sampling leaflets from each plant weekly. The damage was measured by the height of the limit between symptoms of russeting and healthy tissue.
Providing pollen weekly gave the best results, i.e. a higher number of predators and the least symptoms, which remained low during the whole experiment. Results were similar whether fed every two or three weeks. In both treatments, the damage started to increase steadily after two months. However, in all treatments, populations of P. ubiquitus increased quickly at the beginning and a substantial decrease occurred after the demographic peak. Despite the proven efficiency of P. ubiquitus against A. lycopersici, there is still room for improvement. We suggest to aim for a slower population increase to delay the peak and therefore the demographic decline through adapted feeding. Moreover, we initially infested plants with an extremely high amount of pest mites. Despite this, P. ubiquitus was able to reduce the establishment of A. lycopersici. This predator appears to be one of the most suitable biological control agents for greenhouse-grown tomatoes.