Abstract
In 2015, we studied the efficiency of the predatory mite Neoseiulus californicus (McGregor) for suppression of the two-spotted spider mite Tetranychus urticae in a field experiment at a hop plantation. We randomly arranged four treatments in a three-block experiment. Fungicides were used in all treatments; insecticides were used in all treatments except the predatory mite treatment and acaricides were used in only two treatments. A single inundative release of the mite N. californicus was carried out on 4 July. On four different dates (10 June, 17 July, 29 July and 9 August), we counted the eggs and the mobile stages (larvae, nymphs and adults) of the two-spotted spider mite in all four treatments. In the treatment with the predatory mite, we established the fewest eggs and mobile stages of T. urticae 14 days after the release of the predator. The selected acaricides in our research acted in a primarily ovicidal manner, but we did not detect satisfactory effects on the mobile stages of the two-spotted spider mite. This result suggests the emergence of resistance of two-spotted spider mites to the acaricides hexythiazox and abamectin. Our research established comparable effects of the predatory mite N. californicus and acaricides, and further improvement of the efficiency would require release of the natural enemy into a hop plantation in mid-June, followed by a second release three weeks later. The costs of acaricide use in our experiment were from 12.7-fold (two sprayings of hexythiazox, and a single spraying with abamectin) to 17.8-fold (single treatments of hexythiazox and abamectin) lower than those of a single release of the biological control agent in question. The results of our study represent a starting point for future research, which could achieve satisfactory results in suppressing two-spotted spider mites on a hop plantation by repeated use of the predatory mite N. californicus.
Highlights
Hop (Humulus lupulus L.) production is widespread in the countries of Middle Europe
Decisions regarding which synthetic products would be used in our experiment were made according to the IOBC database [13], as we did not want to use products that would have an effect on the predatory mite in the biological control treatment
On 29 July, the highest number of Two-Spotted Spider Mite (TSSM) eggs was recorded for the control treatment (8.1 ± 1.82 eggs/leaf)
Summary
Hop (Humulus lupulus L.) production is widespread in the countries of Middle Europe. Among the notable harmful pests that endanger hop production in the Northern Hemisphere are the damsonhop aphid (Phorodon humuli/Schrank/) and the two-spotted spider mite (Tetranychus urticae Koch) [2]. Both species of harmful pests have begun developing resistance due to the excessive use of insecticides and acaricides [2]. The two-spotted spider mite is among the most important harmful pests in the group of phytophagous mites, as it can develop and feed on more than 1100 species of host plants [3]. If more than 90 adults are found on a hop leaf [3], this mite can cause dire economic damage at harvest time
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