Upregulation of Helicoverpa armigera core RNA interference genes by bacterial infections and its effect on the insect-bacteria interaction.

RNA interference (RNAi) is an extremely conserved defence mechanism. The antiviral role of the RNAi pathway in insects is well documented; however, the relevance of this pathway in other aspects of insect immunity is largely unknown. In this study, we questioned whether RNAi has any function during insect-bacteria interactions. For this, we assessed induction of the RNAi pathway in response to bacterial infections by monitoring the expression of dicer1/argonaute1 and dicer2/argonaute2, which are important genes in the microRNA and short interfering RNA sub-pathways respectively. Bacterial cells of Bacillus thuringiensis and Serratia marcescens were injected into the haemocoel of fifth-instar larvae of Helicoverpa armigera, whereas double-distilled water was injected into control insects. Expression levels of the RNAi-related genes increased in the bacteria-injected larvae compared with controls. Transcript knockdown of dicer1 reduced the replication of B. thuringiensis; as a consequence, larval mortality decreased compared with the control. However, replication of S. marcescens increased following dicer1 silencing, which led to higher rates of larval mortality when compared with the control. RNAi of dicer2 promoted replication of both bacteria in the larvae and also enhanced larval mortality. Therefore, dicer1 and dicer2 affected larval survival and the replication rates of the pathogenic bacteria, suggesting their roles in the interactions.

Physiology of Hibernating Larvae of the Pistachio Twig Borer, Kermania pistaciella Amsel (Lepidoptera: Tineidae), Collected from Akbari Cultivar of Pistacia vera L.

The pistachio twig borer, Kermania pistaciella Amsel (Lepidoptera: Tineidae), a key pest of pistachio trees, is a monovoltine pest living inside the feeding tunnel of pistachio twigs for almost 10 months in a year and overwinters there as last instar larvae. In this study, we measured some physiological parameters of overwintering field collected larvae of the pest. There were no changes in trehalose, glucose, and myo-inositol contents, but there were differences in the levels of total simple sugar and glycogen during overwintering. Total sugar content at the beginning of overwintering (October) was at the lowest level (24.13 mg/g body weight) and reached to the highest level (55.22 mg/g fresh body weight) in November whereas glycogen content was at the highest level (44.05 mg/g fresh body weight) in October and decreased to 18.42 mg/g fresh body weight in November. Decrease in lipid content during the overwintering period was not significant. The highest and lowest levels of protein content were recorded in January and February, respectively. Supercooling points (SCP) of the overwintering larvae were stable and low (ranged between -17.80 and -25.10°C) throughout the cold season and no larva survived after SCP determination. The lowest cold hardiness (60 and 0.0% survival following exposure to -10 and -20°C/24 h, respectively) was observed for in November-collected larvae. Overwintering larvae of the pistachio twig borer rely mostly on maintaining the high supercooling capacity throughout the overwintering to avoid freezing of their body fluid.

Seasonal changes in the cold hardiness of the two-spotted spider mite females (Acari: Tetranychidae).

The twospotted spider mite Tetranychus urticae Koch (Acari: Tetranychidae) is an important agricultural pest. Population dynamics and pest outbreaks highly depend on the overwintering success of the mite specimens; therefore, it is necessary to assess winter survival dynamics of this pest. Seasonal changes in supercooling point (SCP) and acute cold tolerance (2-h exposure at -5, -10, -15, -20, -23, or -25°C) were assessed in field-collected females during the winter in 2010-2011 in Iran. The SCP values varied from a minimum of -30.5°C (January 2011) to a maximum of -12.6°C (April 2011). Significant differences were recorded in the SCP distribution patterns between autumn- and winter-sampled females, depicting the acquisition of cold hardiness over the winter. The mean ambient air temperature was the lowest in January (4°C), when the females showed the highest supercooling ability. Correlated patterns between monthly temperatures and acute cold tolerance also were found. At -20°C, the survival of the mites was very low (10%) when they were sampled in October 2010; whereas it was high (97.5%) in January 2011, before decreasing to 5% in April 2011. The present data show that T. urticae females are chill tolerant and capable of adjusting their cold tolerance over the winter season. Acute cold tolerance (-15 and -20°C) and SCP represent valuable metrics that can be used for predicting the seasonal changes of the cold hardiness of T. urticae females.

Temperature-dependent chemical components accumulation in Hippodamia variegata (Coleoptera: Coccinellidae) during overwintering.

Hippodamia variegata (Goeze) is a widespread predator of aphid and has been reported as the most important naturally occurring enemy of aphids, in many countries. In this study, fluctuating levels of cryoprotectants in nonoverwintering and overwintering coccinellids were assessed in field and natural overwintering sites in Hamadan, Iran, from September of 2010 to June of 2011. Moreover, accumulations of polyols were investigated in response to subzero temperatures. Results demonstrated that concentrations of cryoprotectants changed during the study period under natural conditions. Large amounts of metabolic reserves, in the form of glycogen, accumulated before overwintering. Glycogen began to breakdown but polyols accumulated when ambient temperature decreased from October to December. Overwintering coccinellids displayed a threefold increase in levels of trehalose and a fivefold increase in levels of glucose and total cryoprotectants, but there was even a 45-fold increase in myo-inositol content when subzero temperatures were experienced. It was suggested that myo-inositol and glucose are the major cryoprotectants components in this species. In tests for cold response, the optimal temperature for polyol synthesis seems to be below -3°C. From November to February, all the collected coccinellids that had been kept at 10°C in the laboratory were dead after 30 d, indicating that high temperatures were not favorable for overwintering of this population. Moreover, exposure to high temperatures resulted in rapid catabolism of sugar alcohols. This result demonstrated significant correlation between ambient temperature decrease and accumulation of polyols, suggesting that low temperatures are responsible for polyols synthesis in this species.

Seasonal patterns of cold hardiness and cryoprotectant profiles in Brevicoryne brassicae (Hemiptera: Aphididae).

The cabbage aphid Brevicoryne brassicae (L.) (Hemiptera: Aphididae), one of the most important pests of cruciferous crops, overwinters as nymph and adult on winter cabbages in Tehran, Iran, and forms large populations on these plants during winter. To determine the cold hardiness of this aphid, adults and first-instar nymphs were collected monthly from ornamental cabbages planted in the field from October of 2009 to May of 2010. Supercooling points and LT(50) values (the temperature at which 50% of population died after 24-h exposure to subzero temperatures) were investigated. To elucidate the relation between cold hardiness and cryoprotectants, sugars and polyols were determined by high performance liquid chromatography. Changes of mean supercooling point were small during sampling dates. LT(50) values of adults decreased gradually from -6.9°C in October to -12.2°C in January, showing the increase in cold hardiness during cold seasons. Moreover, nymphs showed similar trends in LT(50) values. Glucose, mannitol, myo-inositol, and trehalose were identified in overwintering aphids. Total amount of the cryoprotectants increased to the highest (72.8 ± 9.2 µmol/g fresh weight) in January. There was a significant correlation between LT(50) values and the cryoprotectant contents, suggesting their important role in aphid cold hardiness. Results have shown that B. brassicae is sufficiently cold tolerant to survive mild winter temperatures and is able to form large populations on winter cabbages, causing it to be considered a threat to early season crops, especially oilseed rape.

Cold tolerance and supercooling capacity in overwintering adults of elm leaf beetle Xanthogaleruca luteola (Coleoptera: Chrysomelidae).

Elm leaf beetle, Xanthogaleruca luteola (Muller) is one of the key pests of elm trees all over the world, and survives winter in reproductive diapause in sheltered locations. Seasonal variation of whole body supercooling points (SCPs), LT50 (temperature at which 50% of the test individuals die) and survival rate after exposure to subzero temperatures were determined in field collected adults during October 2008 to May 2009 and October 2009 to May 2010. The SCP of adults decreased significantly from October (median=-13.8°C) to January (median=-20.7°C) in first year, relatively similar results was observed in the second year. The lowest LT50 was observed in overwintering adults collected in January (-16.81°C) in the first year and December (-15.59°C) in the second year. Mortality at -15°C for 24 h was >70% in early autumn in both years whereas it decreased to lower than 45% in early winter, the highest mortality (100%) was observed in adults collected in May in both years. Cold acclimated adults (30 d, 5°C) in November 2008 exhibited significantly higher SCP (-12.21±0.64°C) than nonacclimated adults (-15.57±1.35°C). A 30-d exposure to 5°C caused >20% mortality in November, while <9% mortality was observed in adults collected in December and January 2008. Overwintering adults died upon freezing and the lower lethal temperatures were within the range of SCP, indicating that X. luteola is a freeze intolerant insect.

Nutritional indices of the cotton bollworm, Helicoverpa armigera, on 13 soybean varieties.

The effects of 13 soybean varieties (356, M4, M7, M9, Clark, Sahar, JK, BP, Williams, L17, Zane, Gorgan3, and DPX) on nutritional indices of the cotton bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae), were determined at 25 ± 1° C, 65 ± 5% RH and a photoperiod of 16:8 L:D. Fourth instar larvae reared on Zane showed the highest efficiency of conversion of digested food (ECD) and approximate digestibility (AD) values (0.299 and 0.867, respectively) compared with other varieties. The lowest value of ECD and food consumed (FC) was on 356 (0.133 and 53.82 mg, respectively). The highest and lowest efficiency of conversion of ingested food (ECI) of fifth instar larvae (0.235 and 0.156, respectively) were on Zane and M4, respectively. The ECI and ECD values of whole larval instars were the highest on M7 (0.524 and 0.820, respectively) and lowest on Sahar (0.279 and 0.353, respectively). However, the highest and lowest value of consumption index (CI) was on M7 (7.351) and BP (3.462). Among the different varieties of soybean, the highest AD value was on M9 (0.858), and the lowest was on Zane (0.597). The results indicated that M4, Sahar, and JK were partially resistant to H. armigera.

Influence of poplar clones on fertility life-table parameters of Chaitophorus leucomelas (Hemiptera: Aphididae).

The aphid Chaitophorus leucomelas Koch (Hemiptera: Aphididae) is one of the most important pests of poplar (Populus spp.) plantations in Iran. In this study, development, reproduction, and life history of the aphid were assessed on 11 poplar clones; belong to three species, Populus nigra L., Populus deltoides Bartram ex Marshall, and Populus. euramericana Guinier. The experiments were carried out under controlled conditions at 24 +/- 1 degrees C, 50-60% RH, and a photoperiod of 12:12 (L:D) h. The developmental time at immature stage ranged from 10 to 12 d. Nymphs reproduced per female were ranged from 49 to 98 nymphs on Populus deltoides var. missoriensis and P. deltoides 72/51, respectively. The intrinsic rate of natural increase (r(m)) varied from 0.176 to 0.264 d(-1) among poplar clones. The r(m) values of the aphids were adversely affected in P. euramericana 242 in comparison with P. nigra 56/72 and P. nigra 63/135. In addition, the jackknife estimates of net reproductive rate (R0) indicated the presence of resistance among poplar clones. R0 ranged from 16.48 on P. nigra var. betulifoli to 47.53 on P. nigra 63/135. Mean generation times (T) was last 17.56 d on P. euramericana 242 to 14.51 d on P. deltoides 69/55. However, doubling time (DT) was 3.87 d on P. euramericana var. grandis to 2.63 d on P. nigra 63/135. The finite rate of increase (lambda) was 1.192 on resistant clone (P. euramericana 242) and 1.302 on susceptible clone (P. nigra 63/135). These results indicate that variation in life-table parameters could be an important component of variation in resistance to C. leucomelas in poplar.

Changes of cold hardiness, supercooling capacity, and major cryoprotectants in overwintering larvae of Chilo suppressalis (Lepidoptera: Pyralidae).

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.

Repellent and fumigant toxicity of essential oil from Thymus persicus against Tribolium castaneum and Callosobruchus maculatus.

Repellent and insecticidal activity of the essential oil extracted from Thymus persicus (Roniger ex Reach. F.) Jalas was evaluated against two stored-product beetles Tribolium castaneum (Herbst) and Callosobruchus maculatus (F.). Dry flowering aerial parts of the plant were subjected to hydro distillation using a modified Clevenger-type apparatus. The repellent and fumigant toxicity were tested against 1-7 days old adult beetles at 27 +/- 1 degrees C and 65 +/- 5% RH in dark condition. The repellency on C. maculatus and T. castaneum at highest concentration (2 microL/mL acetone) was 82.40% and 70.40% respectively. Fumigation bioassays showed that C. maculatus adults were significantly more susceptible (LC50 = 2.39 microL/L air) to the essential oil than T. castaneum adults (LC50 = 234.42 microL/L air). It could be concluded that T. persicus may have potential for applications in management of stored-product pests because of its safety, strong repellency and fumigant toxicity.

Combined effect of gamma radiation and Perovskia atriplicifolia for the control of red flour beetle, Tribolium castaneum.

In order to explore an effective and safe pesticide that could be coupled up with irradiation method, the present study was conducted to determine the synergistic effects of gamma radiation with an essential oil from Perovskia atriplicifolia (Benth) on Tribolium castaneum (Herbst) as a main stored-product pest. Adult insects were exposed to sub lethal doses of gamma radiation and P. atriplicifolia oil, and the mortality was assessed in a short time period after treatment. There was a significant synergistic effect of exposure to gamma radiation and essential oil on 1-7 days old adults of T. castaneum. The potential toxicity of the essential oil on irradiated adults at 900 Gy was synergistically increased. When irradiated adults were exposed to LD5, LD25 and LD50 values of the oil the mortality was increased 8.5, 13.0 and 16.0 times respectively. This combination of irradiation would have a low environmental impact and high compatibility with P. atriplicifolia.