Investigating the impact of temperature and three subspecies of Bacillus thuringiensis on the nodulation of the immune system and some biological parameters of the Mediterranean flour moth Ephestia kuehniella Zeller (Lepidoptera: Pyralidae)

The entomopathogenic bacterium,Bacillus thuringiensis, is a gram-positive and spore-forming bacterium, and a large number of its subspecies have been identified and introduced. The insect immune responses activate after ingesting Bt or its toxin proteins. This research aimed to investigate the effect of temperature and three subspecies including B. thuringiensis subspecies thuringiensis (Btt), B. thuringiensis subspecies aizawai (Bta), and B. thuringiensis subspecies galleriae (Btg) on nodule formation and some biological parameters of the moth Ephestia kuehniella Zeller (Lepidoptera: Pyralidae). A concentration of 109 spore/ml was used to contaminate the larval diet. This experiment was performed at three different temperatures (20, 25, and 30 ºC), relative humidity of 55±5%, and a photoperiod of 16:8 (L: D). The highest number of nodules was significantly observed in Bta and Btg treatments at 30 ºC and the lowest number of nodules was observed in the control. There was no significant difference in the time until pupation at any temperature among the three subspecies. However, a significant difference was observed between different temperatures in each subspecies. Therefore, this duration in the control was significantly affected by temperature. The highest amount of pupa production was related to the temperatures of 20 and 25 ºC in subspecies Bta and the control that had no significant difference. The number of adults obtained in the Bta treatment was not affected by the temperature, similar to the control. Since the temperature did not affect the number of nodules in the control, it is concluded that increasing the temperature by affecting the Bt increased the number of the nodules formed in the surviving larvae and also, the subspecies kind of the bacterium had a significant effect on it.