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Cold hardiness is one of the most common adaptations of insects at low temperatures. To understand the cold hardiness strategy of beet armyworm, Spodoptera exigua (Hübner), six temperature treatments were tested on the last instar larvae. Supercooling points of treatments were not significantly different. Two sugars, glucose and trehalose, as well as three polyols, myo-inositol, glycerol and sorbitol, were identified in these larvae. Trehalose was more affected in response to low temperatures in longer duration, and had a significant negative correlation with glycogen content. Despite the extensive sugar beet cultivation areas in Iran, beet armyworm population has been decreased in recent years. It seems that climate change regarding the global warming especially in autumn and winter could be a reason for decline in population outbreak of beet armyworm in the next generation. Based on findings of this study, it is suggested that overwintering larvae are freeze-intolerant insects but long term acclimation at sub-zero temperatures makes larvae tolerate presence of ice crystals in their body fluid.  

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The overwintering conditions and cold tolerance of the Lime butterfly, Papilio demoleus L., are relatively unclear. In the present study, overwintering pupae were collected over several months, and changes in supercooling point (SCP), cold-hardiness, and body color were investigated. Also, some eggs were collected and reared in the laboratory, and then pupae were kept for 1-4 weeks at 0, 5, and 15 °C, and the changes in SCPs were studied. Shelters were prepared and installed in the field to check the overwintering sites. Also, the digestive tract was investigated before and at the beginning of the overwintering phase. The results showed that the SCP gradually decreased from -9 to -13 °C during the autumn months, and in lab-reared pupae treated at 0-5 °C, the SCP was reduced to -13 °C. None of the pupae survived at temperatures below the SCP, so this species uses a freeze avoidance strategy. As the weather gets cold, the color of most of the pupae (76.19%) tends to brown, while in the summer months, more than 80% of the pupae are green. The overwintering pupae emptied their ingested foods, and the contents of their digestive system before emptying contain Pseudomonas and Enterobacter species, both of which can act as ice nucleators. Ultimately, the relationship between these factors in adapting the pest to low temperatures was discussed.

 

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Diatomaceous Earth (DE) is a dust composed of fossilized bodies of unicellular algae used as an insecticide. In this study, the insecticidal potential of four Iranian DE deposits was assessed in adults of Oryzaephilus surinamensis (L.). Three of DE deposits were collected from Maragheh, Mamaghan, and Khorasan Jonoobi mines and Sayan^® formulation was obtained from Kimia Sabz Avar Company. The insect adults were exposed on wheat, peeled barley, and rice treated with 300, 600, 1,000, 1,500, and 2,000 ppm of the DE deposits. Experiments were conducted at 27±1°Cand 55±5% RH in continuous darkness. Mortality of the exposed individuals was counted after 2, 5, 10, and 14 days of exposure on the treated substrate. Mortality increased with increasing exposure intervals and concentration level. Satisfactory level of protection was observed on wheat grain; as 100% mortality was recorded on wheat treated with 600 ppm of all tested DE deposits after a 10-day exposure. However, for rice, even after 10 days of exposure to 2000 ppm mortality didn’t reach 100%. The lowest LC₅₀ value (39 ppm) was obtained in wheat treated with Khorasan DE sample and the highest one (908 ppm) was achieved in rice treated with Sayan^®. The present study suggests that Iranian DEs may be used as potential grain protectants in stored-product pest management programs.

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The European corn borer Ostrinia nubilalis (Hübner), as a worldwide corn pest, causes serious damages. In the present study, some biological aspects of O. nubilalis were investigated on three different host plants including corn stalks, potato, and soybean stems, and a specific semi-artificial diet. Once appropriate host was selected, developmental rates of eggs, larval and pupal stages as well as moth emergence, longevity, and female fecundity were determined at four constant temperatures (20, 24, 28, and 32±1°C). The relationship between temperature and developmental rate was estimated with two linear models under laboratory condition (70-80% RH and a photoperiod of 16L:8D hour). Results showed significant differences between studied foods, such that corn stalk sections and semi-artificial diet were appropriate host for O. nubilalis compared to the other two hosts. It was also revealed that optimum temperature for growth of this pest was 28°C. Lower developmental threshold estimated by traditional and Ikemoto-Takai linear models for whole immature stages were about 9 and 10°C, and thermal constants were 473 and 431 degree day (DD), respectively. Compared to previous studies, these values were similar in the immature stages, except for the larval stage, which could indicate the importance of nutrition and role of the plant host in temperature requirements.