The population fluctuations of adult palm beetles, Oryctes agamemnon mathiesseni and O. elegans in Mahshar date palm orchards of Khuzestan

Date palm borers are among the most important pests of date trees in Iran. This study aimed to determine the population fluctuations of rhinoceros beetles Oryctes sp., infesting the date palm Phoenix doctylifera, using light traps in Mahshar date palm orchards. Samplings were weekly conducted from 2021 to 2022 in two randomly selected date palm orchard. Over two years of monitoring coleopteran adults, two species of the genus Oryctes namely O. agamemnon mathiesseni and O. elegans were observed. The beginning seasonal activity of both univoltine species was middle May, reaching the peaks during summer, and the populations declined gradually till October. In each of research years, one of two species was dominant, so that in the first year, the number of adult beetles of O. agamemnon mathiesseni was significantly more than O. elegans, while in the second year, the number of O. elegans was higher. In both sampling years, the activity of dominant species in that year started earlier, and ended later. A two-year study of the sex ratio in these horned beetles revealed that females outnumbered males substantially (2.5 to 4 times in two years) in the subspecies O. agamemnon mathiesseni. For O. elegans, this ratio ranged from 1.5 times (2021) to 2.5 times (2022). The successful IPM programs are effectively dependent on prediction of the emergence time and population fluctuations of pest insects, and it is hoped that the results of this study will be useful to control of the rhinoceros beetles.