Biological Control of Date Palm Mite Oligonychus afrasiaticus (McGregor) (Acari: Tetranychidae) Using the Predatory Mite Euseius scutalis (Athias-Henriot) (Acari: Phytoseiidae) Under Laboratory and Field Conditions

The date palm mite Oligonychus afrasiaticus is one of the most destructive phytophagous pests in date palm orchards and can cause severe economic losses when not effectively managed. Although chemical acaricides remain the primary control method, their adverse effects on natural enemies, environmental quality, and human health underscore the need to reduce reliance on chemical inputs and develop sustainable biological control strategies, including the use of acarine predators. Accordingly, this study aimed to evaluate the efficacy of the predatory mite Euseius scutalis as a biocontrol agent against O. afrasiaticus under both laboratory and field conditions. In addition, the biological characteristics of E. scutalis, a key predator of O. afrasiaticus, were examined under controlled laboratory conditions. All experiments were carried out on kidney bean discs in an incubator at 32 ± 1 °C, 50% RH, with 14:10 h L:D. Euseius scutalis completed development, survival, and oviposition on O. afrasiaticus as prey. The average developmental period for males was 5.17 days, and for females, it was 5.64 days; the average adult female longevity was 11.67 days. The average daily and total egg production were 2.81 and 48.90 eggs, respectively. The sex ratio was 0.70 females, and the death rate of immature stages was 0.66%. The intrinsic rate of increase (rm) was 0.281 females/female/day, the mean generation time (To) was 12.36 days, and the net reproduction rate (Ro) was 14.25 females/female. Experimental releases of the predatory mite E. scutalis were conducted in conventional date palm (Phoenix dactylifera L.) orchards in the Qassim region of Saudi Arabia. Three predator release rates (200, 400, and 600 individuals per date palm tree) were evaluated on two date palm cultivars, Barhi and Sokary, to assess their effectiveness against O. afrasiaticus. The release rate of 200 individuals/date palm tree did not provide effective control of O. afrasiaticus. When it was released at 400 and 600 individuals per tree, E. scutalis maintained the O. afrasiaticus population below the economic threshold of 4 moving stages per fruit. Hence, it can be recommended, considering these findings, to increase the number of E. scutalis when controlling O. afrasiaticus in heavily infested varieties to acquire date fruits devoid of acaricide residues and dust mites.