The rice stem borer, Chilo suppressalis Walker, which is a key rice pest in northern parts of Iran, overwinters in rice stubble and weeds as mature larvae. Diapause of this pest is initiated between October to November and terminates in March. Seasonal variations in the supercooling point, survival at low temperatures, and sugar contents were studied in field-collected larvae during different phases of diapause. Ambient temperature was lowest in January and February when larvae were at the highest diapause intensity and achieved a high degree of cold hardiness at -10, -15, and -20 degrees C. Glycerol, a major cryoprotectant, reached a peak in January. It appeared that cold hardiness in the larvae is closely associated with the diapause. For the first time, this study suggests that glucose and glycogen are converted to glycerol during cold seasons, but trehalose has no definite role in the interconversion. During the coldest months, supercooling points (SCPs) increased (around -11 degrees C), and larvae could survive below their SCP values, showing that overwintering larvae of C. suppressalis are freeze tolerant in Iran. Our findings suggest that cold hardiness and diapause are essential components for this species. The overwintering larvae have high capacity of cold hardiness and can overcome severe winters. Understanding of cold hardiness and overwintering behavior of this species may help in integrated pest management of the rice stem borer in paddy fields.

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Citrus leafminer (CLM), Phyllocnistis citrella Stainton (Lepidoptera: Gracillariidae), and European corn borer (ECB), Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae), are two key pests of young citrus and maize plants in Iran, respectively. In this study, the effects of sub‐sterilizing doses of gamma radiation (100–250 Gy for CLM, 90–180 Gy for ECB) on the biological and reproductive parameters of F1 progeny from irradiated males were determined. The results indicated that males irradiated at doses of ≥200 and ≥150 Gy produced highly sterile F1 descents for CLM and ECB, respectively. No adverse effects of radiation doses applied to males were observed on the F1 pupal emergence for both species, nor on the adult longevity of male and female ECB moths. However, the life span of CLM F1 male and female adults decreased with increasing doses. The sex ratio of emerged adults of F1 progeny from irradiated males was skewed towards males with increasing doses; the proportion of males to all emerged adults reached 0.52 and 0.54 at doses of 250 and 150 Gy for CLM and ECB, compared to 0.44 and 0.49 in the controls, respectively. The competitiveness index of irradiated and F1 males of both species fluctuated in acceptable ranges and in general F1 males were stronger competitors than their irradiated male parents. The results of the field cage experiments showed that the larval infestation in all cages including the released irradiated CLM and ECB moths decreased compared to the control treatment – the percentage of damaged leaves and stems in the cages with ratios of 20:1 and 7:1 irradiated‐to‐normal insects (highest ratios assayed) reached half and one‐third of the control for CLM and ECB, respectively.

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Phyllocnistis citrella Stainton (Lepidoptera: Gracillariidae), also known as the citrus leafminer, is a serious pest in Citrus Linnaeus (Rutaceae) nurseries in Iran. Few studies have been performed on the life history of this pest on different citrus hosts. In this work, the infestation rate and biological aspects of P. citrella were investigated using four citrus hosts: Valencia orange (Citrus sinensis (Linnaeus) Osbeck), trifoliate orange (Poncirus trifoliata (Linnaeus) Rafinesque), grapefruit (Citrus paradisi Macfadyen), and sweet lemon (Citrus aurantifolia Swingle). Moths preferred laying eggs on leaves with a width ranging from 1–2 cm, and the highest oviposition was observed on the Valencia orange (51.2 eggs/female). The numbers of pupae and infested leaves were significantly higher on C. sinensis and C. aurantifolia. The entire developmental period of the immature stages was 13.8 and 15.4 days in C. aurantifolia and C. sinensis, respectively, while it increased to 21.8 and 24.7 days in C. paradisi and P. trifoliata. The rate of mortality of the immature stage was the highest in these two latter hosts as well (29–31%). Moths showed the highest emergence and longevity on C. sinensis and C. aurantifolia. The results indicate that C. sinensis and C. aurantifolia are susceptible hosts that can be recommended for the mass-rearing of this species in non-chemical pest control programmes.

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