Overwintering and Alternative Hosts of Dust Mites Oligonychus afrasiaticus (McGregor) on Date Palm in Iraq

Abstract

The dust mite Oligonychus afrasiaticus (McGregor) on date palm trees is one of the main pests affecting palm trees in Iraq. Its severity has increased its damage to the crop in recent years. A study of some environmental aspects of the pest such as alternative hosts, spread and distribution of the pest after harvesting and overwintering are important factors to identify pest's vulnerable periods, which can be utilized in the control process. The results revealed that the pest had activity during the spring on alternative hosts Sorghum bicolor, S. halepense, and Cynodon dactynlon. Surveying vegetables that are inter-planted with palm groves, the pest was found present in the field on the Fragaria ananassa, Cucurbita pepo, Solanum melongena, and Citrullus lanatus. At the "rutab" and "tamar" stages, higher numbers of O. afrasiaticus began to leave the dates fruit bunches to pinnae of frond trees and offshoot to feed and reproduce until the onset of winter and remain there as fertile females to resume their activities during the following spring. The highest density of mobile instars and eggs reached 0.9 individual/pinna and 1.4 egg/pinna, respectively, in October, and then the numbers began to decline to reach 0.3 individual/pinna during the winter period, when no eggs were observed. Furthermore, some plant species provided food and shelter for the pest during the winter period such as C. dactylon, S. halepense, Imperata cylindrica and Phragmites australis. Results obtained also showed that date palm seedlings grown randomly in the orchard under study acted as a refuge for the dust mite, as it fed and multiplied continuously on them for several generations and throughout the year. Keywords: Oligonychus afrasiaticus, overwintering, alternative hosts