Document Type : Complete paper
Authors
1 Department of Biodiversity, Institute of Science and High Technology and Environmental Sciences, Graduate University of Advanced Technology, Kerman, Iran
2 Department of Biotechnology, Institute of Science and High Technology and Environmental Sciences, Graduate University of Advanced Technology, Kerman, Iran
Abstract
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Main Subjects
Extended Abstract
Bacillus thuringiensis is a Gram-positive and spore-forming bacterium that has special toxicity for different orders of insects and can point out three subspecies B. thuringiensis subspecies thuringiensis (Btt), B. thuringiensis subspecies aizawai (Bta) and B. thuringiensis subspecies galleriae (Btg). Insects can activate their immune responses after consuming Bt or toxin proteins for defence. The purpose of this research is to investigate the effect of temperature and three subspecies of insect pathogenic bacteria including Btt, Bta and Btg were found to affect the production of nodules concerning the immune system of E. kuehniella larvae and some biological parameters of this moth such as the number of produced pupae, the period till pupation and the number of adults. This experiment was performed at three different temperatures (20, 25 and 30ºC), the relative humidity 55±5% and a photoperiod of 16:8 (L: D). The results showed that the interaction of bacterium and temperature on the number of nodules formed in larval hemolymph, the duration of 24-day-old larvae turning into pupae, and the number of pupae and adults produced were significant. In the case of all three subspecies of bacterium, the highest number of nodules was significantly formed at 30 ºC. However, the difference was not significant between the other two temperatures (20 and 25ºC). The lowest amount of nodules was significantly observed in the control and showed that temperature does not affect the number of nodules formed in larval hemolymph. There was no significant difference between the three subspecies in the time until the pupation of the larvae at any temperature. However, a significant difference was observed among different temperatures in each subspecies. Likewise, this duration in the control was significantly affected by temperature; therefore, this process took more time at 20 than 30ºC. The number of pupae produced in each of Btt and Btg treatments was the same at all three temperatures and no significant difference was observed between different temperatures. However, in Bta treatment at 30ºC, pupal production decreased significantly that was similar to the control. The highest amount of pupa production was related to the temperatures of 20 and 25 ºC in Bta and the control treatment did not have significant differences. At the temperature of 30ºC, there was no significant difference in the number of pupae produced between the three studied subspecies. The number of adults obtained in the Bta treatment was not affected by the temperature, similar to the control. While, in Btt and Btg subspecies, the lowest number was significantly obtained at 30 and 25ºC, respectively. In other words, a significant difference was revealed in the number of adults obtained among the three subspecies of the bacterium at two temperatures of 25 and 30ºC that were less than the control. In general, the average duration of transformation of bacteria-infected larvae to pupation was less than that of the control. The effects of environmental changes on insect immune responses are not strong. Since the temperature did not affect the number of nodules in the control, it is concluded that increasing the temperature by affecting the Bt bacterium increased the number of the nodule formation in the surviving larvae and also, the subspecies of the bacterium had a significant effect on it. It seems that for this reason, the treatment of 5th instar larvae with Bta and Btg subspecies at 30ºC caused the highest number of nodules in the hemolymph of larvae without significant difference between these two subspecies. Perhaps this has caused these two treatments to have no difference in the number of pupae and adults created compared to the control. Another result recorded in the present study showed that the increase in temperature caused the 24-day-old larvae to enter the pupal stage faster. This trend was observed in the bacterial treatment (in each of the subspecies) and the control. Of course, infected larvae entered the pupal stage even earlier than healthy larvae. This strategy is to escape from the adverse effects of bacterium and increase in temperature. Because it has been proven that the sensitivity of Lepidopteran larvae to Bt bacterial toxins is higher than that of adults (Lu et al. 2012). The results showed that no more pupae were formed in bacterial treatments from the 9th day after infection at high temperature and the 13th day after infection at low temperature. It seems that this issue happened due to the death of some larvae due to bacterial infection and it is more evident in the case of Btt subspecies in all three temperatures.