Impact Temperatures on the Biological Characteristics of the Bio-parasitoid Trichogramma spp. Reared on the Eggs of the Lesser Date Moth Batrachedra amydraula (Meyrick).

Abstract

Lesser date moth Batrachedra amydraula presents an important threat to the sustainability of date palms in the Shatt Al-Arab district of Basra. This research established two potential egg parasitoids Trichogramma evanescens and T. brassicae through comparative analysis of their physiological and field performance. Additionally, we looked at the thermal optimum and biological response of each species across three set temperatures 25°C, 30°C and 35°C on three popular varieties of date palms Sayer, Halawi and Khadhrawi. Laboratory trials were completed within programmed incubators to determine four important measurements relevant to each species analyzed: total rates of parasitism; total adult emergence, total embryos lost, and sex ratio. All laboratory results were combined with monthly data from in situ fields February through June to better match laboratory and real world performance. The data suggests that when both T. brassicae and T. evanescens achieved maximum physiological performance, there was a thermal pivot point at a temperature of 30 °C with 80.11% total parasitism for T. brassicae and 79.93% for T. evanescens on Halawi date palms, the temperature at which both species had optimal parasitism rates. The temperature increase to 35°C caused a rapid decline in efficiency to less than 55% as a result of metabolic stress related to female vitality. For T. evanescens, the highest percentage of emergence 64.2% and the lowest percentage of mortality 35.8% occurred at the optimum temperature, in contrast, T. brassicae had a high rate of embryonic mortality of 49.43% at 35°C, suggesting that T. brassicae was very sensitive to heat. The highest frequency of field activity was found in April on Khadhrawi palms. Halawi expressed the highest biological compatibility 57 to 62.5% female biased sex ratio based on laboratory evaluations. The study identifies 30 as the gold standard for mass raised and in field use. Based on its overall biological fitness, T. evanescens is the strategic selection for use in IPM programs in southern Iraq. The results recommend a timeframe to release in the field during April, the biological window when field temperature is compatible with physiological optima to maximize insect pest suppression prior to reaching extremes in thermal conditions during June.