Field Population Sex Ratio of the Date Palm Mite, Oligonychus afrasiaticus (McGregor)

The effect of some abiotic and biotic factors on the population sex ratio of the date palm mite (DPM), Oligonychus afrasiaticus, were evaluated on four date palm cultivars in two regions (Riyadh and Qateef) of Saudi Arabia. The week of infestation, fruit stage, and their interactions, as well as the cultivar, significantly affected the DPM sex ratio. The DPM infestation, in the first week, started with a high female proportion (from 0.78 to 1) in both regions of the ‘kimri' fruit stage, and remained female-biased till the fifth week of infestation (from 1.5:1 to 4:1) with a growing DPM population density in both regions. The DPM sex ratio declined to equality (1:1) during the sixth week of infestation, the onset of the ‘khilal’ fruit stage, and further declined to a male-biased sex ratio (4:1) on the Selj, Hamra and Shaishie cultivars, with a declining DPM population density in the last week of infestation. The date fruit stage affected the sex ratio of DPMs negatively in Riyadh and positively in Qateef. The interaction between the week and fruit stage had a significant positive effect on the DPM sex ratio in Riyadh, and a negative effect in Qateef. This study of the DPM sex ratio could be a step in establishing a female-based sampling programme during the early weeks of infestation.