Determination of economic injury level of date palm lesser moth, Batrachedra amydraula (Lepidoptera: Batrachedridae) on six commercial date cultivars in Iran

The small date moth Batrachedra amydraula Meyrick (Lepidoptera: Batrachedridae) and other date palm moths are among the most important date fruit pests, causing the date fruits to dry and fall. This study aimed to investigate the relationship between the density of B. amydraula population and the extent of its injury level as well as between the rate of damage and reduction of date yield indices on six commercial date palm cultivars in five provinces of Iran including Khuzestan, Bushehr, Hormozgan, Kerman and Saystan & Baluchestan durying 2018 and 2019. Production management costs in both chemical and biological control approaches were considered. Also, crop prices in each region were calculated based on a six-month average prediction. Sampling were done at 15-days intervals from May to early September. To this end, four clusters were selected from four different geographical directions of each tree and in each cluster, 25 fruits were checked to determine the number of healthy and infested fruits. Finally, the Norton model was used to calculate EIL under biological and chemical control conditions. Based on the results, the cost of biological control was lower than that of chemical control. The highest cost in both methods was the cost of purchasing the controlling materials. The highest rate of injury (symptoms of nutrition) to the crop was observed in Mazafati cultivar and the lowest one was in Kabkab. Also, the highest crop damage (nutrition losses) caused by pest damage unit was observed in Rabi cultivar and the lowest one was in Kabkab cultivar. In all studied cultivars, the economic injury level in 2018 was lower than 2019 in both chemical and biological control methods. On the other hand, in biological control method in both years and on all cultivars, costs were lower than chemical control method. The highest value of economic injury level in 2019 was estimated for cultivar Sayer in biological control method (1546.1 larva-day) and the lowest one was estimated for cultivar Rabi in chemical control method (13.81 larva-day).