Induction of diapause by clock proteins period and timeless via changes in PTTH and ecdysteroid titer in the sugar beet moth, Scrobipalpa ocellatella (Lepidoptera: Gelechiidae)

The sugar beet moth, Scrobipalpa ocellatella (Boyd), one of the most severe sugar beet pests, causes quantitative and qualitative yield losses late in the autumn. Previously, it was shown that low temperature and short-day photoperiod together cause diapause induction in pupae. Here, the interaction of the critical elements of the diapause induction, including the period (PER), timeless (TIM), prothoracicotropic hormone (PTTH), and ecdysteroid titer, were investigated. Immunohistochemistry results showed that the number of period immunoreactivity (PER-ir) and TIM-ir cells in nondiapause pupae (NDP) was lower than in the brain of the diapause pupae (DP). Moreover, the number of PER-ir and TIM-ir cells in the protocerebrum and optic lobe (OL) of NDP was lower than DP. Moreover, lower PTTH content in the brain and hemolymph of DP was confirmed by competitive enzyme-linked immunosorbent assay. Enzyme immunoassay showed a lower 20-hydroxyecdysone (20E) titer in the hemolymph of the DP compared with the NDP. Within a short-day condition, PER and TIM titers increased in the brain leading to decreasing PTTH titers in the brain and hemolymph that caused decreasing 20E titer in the hemolymph, leading to the induction of diapause. This study suggests that PER and TIM could be one of the brain factors that play an essential role in regulating diapause in S. ocellatella.

Thermal tolerance variations and physiological adjustments in a winter active and a summer active aphid species

The Russian wheat aphid Diuraphis noxia (Kurdjumov) and melon aphid Aphis gossypii Glover are known as winter and summer active species, respectively. It is hypothesized that differences in the aphids' seasonal activities might be related to their response to temperature extremes and different physiological mechanisms. To study the aphids' thermal tolerance variations and mode of their physiological basis, they were cold acclimated at 20, 15, 10, 5, and 0 °C for 168 h (7 days) and heat acclimated at 20, 25, 30 °C for 168 h and 35 °C for 48 h. At the end of each thermal regime, survival at low and high temperatures was determined, and changes in sugars and polyols and heat shock protein 70 (Hsp70) were investigated. D. noxia was more cold-tolerant, while A. gossypii was a more heat-tolerant insect. The type and pattern of sugars and polyols were similar in both species under cold acclimation (ACC) and heat acclimation (HCC). In both species, glucose and mannitol were the major identified compounds involved in cold and heat tolerance. However, they showed different patterns of Hsp70 level, with D. noxia having a higher level of Hsp70 under ACC and A. gossypii having a higher level of Hsp70 under HCC. These results demonstrated that their differences in thermal tolerance might explain the seasonal activities of the aphids.

Erucin modulates digestive enzyme release via crustacean cardioactive peptide in the elm leaf beetle Xanthogaleruca luteola (Coleoptera: Chrysomelidae)

Plant secondary metabolites influence the feeding in insects through several modes of action. In this study, the physiological effects of erucin isothiocyanate were investigated on the elm leaf beetleXanthogaleruca luteola(Müller) (Coleoptera: Chrysomelidae) via impact on crustacean cardioactive peptide (CCAP) and midgut digestive enzymes. Third instar larvae of elm leaf beetle were fed on leaves impregnated with erucin for three days. The results showed that erucin decreasedα-amylase, lipase, and protease release. Western blot analysis and competitive ELISA showed that erucin decreased CCAP content of the midgut, brain, and hemolymph. Moreover, incubation of dissected midgut with CCAP and also its injection into the hemocoel increased digestive enzyme release. It could be concluded that erucin isothiocyanate decreases CCAP content that itself led to a decrease in digestive enzyme release. Also, it suggests that CCAP could be one of the factors, regulating feeding activities in the elm leaf beetle. This report shows that CCAP is both a midgut factor and a neuropeptide that regulates digestive enzyme release in the elm leaf beetle and could be used to study erucin effects in insects.

The trypsin inhibitor pro-peptide induces toxic effects in Indianmeal moth, Plodia interpunctella

The inhibitory potential of an inhibitor peptide based on the pro-region of trypsin zymogen was investigated in Indianmeal moth, P. interpunctella, which is a world-wide insect pest of stored food. Five peptides were designed based on molecular docking simulations. The designed peptide with the best score was selected and synthesized for further screening in vitro and in vivo. The peptide was characterized and its inhibitory effects towards the insect trypsin were evaluated and the kinetic analysis revealed a competitive type of inhibition against the target enzyme. The results showed that the peptide could successfully suppress the pest midgut trypsin, and more interestingly, it did not show considerable inhibitory effects on a mammalian trypsin. We also aimed to assess the effect of dietary insect meal treated with different concentrations of the peptide and observed a significant growth and development retardation in pupa and adult insects fed with the inhibitor peptide. The outcomes of the present study suggest an efficient inhibitor peptide that could specifically bind the P. interpunctella trypsin and inhibit its activity, which would be safe against human being health and environment. Notably, this is the first report on in vivo assessment of the direct effect of a pro-region as the specific inhibitor in development as well as survival of the pest insect. Furthermore, our findings could be a promising for future designed pesticides used in pest management.

Induction of DNA methyltransferase genes in Helicoverpa armigera following injection of pathogenic bacteria modulates expression of antimicrobial peptides and affects bacterial proliferation

Following pathogen attack in a host, widespread changes are induced in the host's gene expression, in particular those involved in the immune system, growth and survival. Epigenetic mechanisms have been suggested to be involved in the regulation of these changes through a number of mechanisms. DNA methylation is one of the important epigenetic processes that is carried out by DNA (cytosine-5) methyltransferase (DNMT) and alters expression of target genes. Here, we identified two putative sequences of DNMT (i.e. DNMT1 and DNMT2) from the transcriptome dataset of Helicoverpa armigera that showed high similarity to the homologous sequences in Bombyx mori. Domain architectures of DNMT1 and DNMT2 exhibit the unique pattern of DNMTs that highlights conserved function of these genes in different insects. To see if these genes play any role in bacterial infection, we challenged the fifth instar larvae of H. armigera by injecting Bacillus thuringiensis and Serratia marcescens cells into the hemolymph. Transcript levels of the DNMTs were analyzed by RT-qPCR. The results showed that the expression levels of DNMT1 and DNMT2 increased in the bacteria-injected larvae. Injection of the heat-killed bacteria also induced the expression of the DNMTs, but lower than that of the live bacteria. To determine whether these genes function during bacterial infection, we injected the inhibitor of DNMTs, 5-azacytidine (5-AZA), into the larvae and 24 h later, the bacterial cells were also injected into the larvae. Bacterial replication and larval mortality were analyzed in the treated and control insects. We found that 5-AZA reduced bacterial replication and also mortality of the bacterial-injected larvae regardless of the pathogenic bacterial species. Interestingly, the expression levels of antimicrobial peptides (AMPs) were also modulated following 5-AZA treatment. In conclusion, we showed that upregulation of the DNMTs in H. armigera following bacterial infections modulates AMPs and thereby affects the insect-bacteria interactions.

The microRNA pathway core genes are differentially expressed during the development of Helicoverpa armigera and contribute in the insect's development

MicroRNAs (miRNAs) are small non-coding RNAs (18-25 nt) that are produced by all animals and plants as well as some viruses. Their roles have been revealed in many physiological processes including development, cancer, immunity, apoptosis and, host-microbe interactions through post-transcriptional regulation of gene expression. In this study, we predicted, characterized and transcriptionally analyzed the core miRNA pathway genes in Helicoverpa armigera. Our results showed that the canonical miRNA biogenesis pathway genes including Pasha, Drosha, Loquacious, Exportin-5, Dicer-1 and Argonaute-1 are differentially expressed in different tissues and during the development of this insect. Considering the essential role of Dicer-1 in this pathway, we used RNA interference to silence the expression of this gene in H. armigera. Silencing of Dicer-1 decreased the levels of cellular miRNAs, let-7 and miR-184. Together, our results showed that the miRNA pathway functions during the development of H. armigera, and silencing of Dicer-1 resulted in the miRNA pathway blockage and depletion of the miRNA contents leading to mortalities in the immature stage and abnormalities in the mature stage. Blockage of this pathway can therefore be considered in future attempts for interrupting/suppressing populations of this important crop pest.

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.

The Effect of Temperature and Photoperiod on Diapause Induction in Pupae of Scrobipalpa ocellatella (Lepidoptera: Gelechiidae)

Scrobipalpa ocellatella (Boyd) (Lepidoptera: Gelechiidae) is one of the most important pests of sugar beet that causes quantitative and qualitative yield loss in the late summer. To locate the position for diapause induction, combinations of constant temperatures at 15, 18, 20, and 25°C and day lengths of 8, 10, 12, 14, 16, and 24 h were studied from egg to adult emergence. The incidence of diapause peaked at 15 and 18°C, with the day lengths of 12 and 11 h, whereas low temperatures did not improve the effects of short photoperiods (day lengths of 8 and 10 h) in diapause induction. The results showed that the critical day length for diapause induction was 12.8 h at overall 15 and 18°C. It was observed that the third instar larvae were the most sensitive stage to the inductive photoperiod (12:12 [L:D] h). The non-24-h light-dark experiment showed that the nigh length is more important than the day lengths measurement. In a set of 24-h light-dark cycles at 2:12 (L:D) h, a 1-h light pulse declined diapause induction markedly 1 h after scotophase. Field monitoring of the S. ocellatella for 2 yr (2015 and 2016) showed that the 50% of larvae enter winter pupal diapause in early September and this proportion increases in response to a decrease in the day lengths and temperature. From this study, it was concluded that low temperature acts in conjunction with short-day photoperiod in diapause induction of S. ocellatella.

Diapause Induced by Temperature and Photoperiod Affects Fatty Acid Compositions and Cold Tolerance of Phthorimaea Operculella (Lepidoptera: Gelechiidae)

To find out the potential condition for diapause induction in the potato tuber moth Phthorimaea operculella (Zeller), combination of constant temperatures (15, 20, and 30°C) and photoperiods (8, 9, 10, 11, 12, 14, and 16 h) were employed from egg to adult emergence. In addition, changes in the total phospholipid fatty acid content and cold tolerance of non-diapausing and diapausing pupae were examined. The critical daylength for diapause induction were 12.43 h at 20°C and lower temperatures that can induce in 50% of population. Moreover, the composition of total phospholipid fatty acids in the pupae revealed seven major fatty acids in both non-diapausing and diapausing pupae: oleic (26-32%), palmitic (21-29%), linoleic (18-21%), palmitoleic (4-10%), stearic (9%), linolenic (7-8%), and pentadecanoic acids (3-5%) with an increase in proportion of unsaturated fatty acids in diapause state. In contrast to increase of oleic acid (C18:1) from 26 to 32% in non-diapausing to diapausing pupae, a decrement trend from 29 to 21% in palmitic acid (C16:0) was observed at the same state. Additionally, supercooling point was observed to be significantly lower in diapausing (-22.6°C) than in non-diapausing pupae (-18.5°C) and the fresh weight of diapausing pupae was found to be significantly higher than non-diapausing ones. The significance of these findings would allow us a better understanding of interrelationship between diapause and cold tolerance.

Rapid Cold Hardening Capacity and Its Impact on Performance of Russian Wheat Aphid (Hemiptera: Aphididae)

The Russian wheat aphid, Diuraphis noxia (Kurdjumov), is one of the most important pests of wheat and barley in most wheat-producing countries. Rapid cold hardiness (RCH) is a capacity of insects to develop, within hours, protection against subfreezing temperatures that plays an important role in aphid survival in response to sudden decreases in air temperature. In this research, we investigated the duration and rate of cooling on the induction of RCH of D. noxia and the costs of RCH on aphid development and fecundity. By transferring aphids directly from 20 °C to a range of subzero temperatures for 2 h, the lower lethal temperature for 80% mortality (LT80) was determined to be - 11.9 °C. Preconditioning the aphids at 0 °C for 1-3 h prior to exposure at (LT80) (-11.9 °C) resulted in a sharp increase in survival, with little change with longer durations of preconditioning. The slowest cooling rate (0.05 °C/min) increased survival fourfold, whereas rates from 0.1 to 1 °C/min increased survival twofold compared with a direct transfer to 0 °C, regardless of aphid stage used. Deleterious effects of RCH were not observed on aphid development, longevity, or fecundity. The present study indicates that RCH is induced in D. noxia in just a few hours in response to sudden lowering of temperatures to freezing, with little or no cost in reproductive capacity.

Physiology of Cold Hardiness, Seasonal Fluctuations, and Cryoprotectant Contents in Overwintering Adults of Hypera postica (Coleoptera: Curculionidae)

The alfalfa weevil, Hypera postica (Gyllenhal), is widely distributed in various alfalfa-growing regions in the world. Adults enter the field gradually from hibernation places and overwinter in a nondiapausing state, exhibiting feeding, mating, and oviposition over autumn and winter whenever the weather permits. In this study, the variability of supercooling point (SCP) and cold hardiness in alfalfa weevil was investigated. Adults were collected monthly from alfalfa fields in Karaj, Iran, during autumn, winter, and spring in 2011-2012. Supercooling points and LT50 (exposure at subzero temperatures from -5 to - 13 °C for 24 h and 50% death of the sample) were studied. The average SCP varied from -14.4 ± 0.7 °C in October to - 8.7 ± 0.4 °C in May. Mean SCPs were significantly lower during autumn (-13.4 °C) than winter months (-8.6 °C). The frequency distribution of SCPs in individuals in autumn was bimodal and in winter was unimodal. Insects could survive after exposure to -5 °C in all months, but mortality increased with cold intensity. Percent mortality at -11 °C was ∼89% in November and December and then increased to 100% in January and February. The approximate LT50 values were -5.7 °C and -6 °C in January and February, respectively. Seasonal changes in sorbitol, glycerol, glucose, and trehalose were consistent with a role in freeze protection. However, microhabitat may also play an important role in protecting insects from cold weather and allowing them to tolerate low temperatures and increase their population.

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.

Sublethal Effects of Fenoxycarb on the Plutella xylostella (Lepidoptera: Plutellidae)

The effects of fenoxycarb, a Juvenile hormone analogue, at sublethal concentrations were tested on some biological parameters of Plutella xylostella (L.) in two consecutive generations. The calculated LC10, LC25, and LC50 values of the insecticide were 21.58, 43.25, and 93.62 mg/liter on third-instar larvae, respectively. Fenoxycarb significantly reduced pupal weight and oviposition period in parent generation. In addition, the fecundity of treated groups (LC10 = 71.06, LC25 = 40.60 eggs per female) in parents was significantly lower than control (169.40 eggs per female). Although fenoxycarb could not affect gross reproductive rate and death rate, it decreased net reproductive rate, intrinsic rate of increase, finite rate of increase, and birth rate in offspring generation. Also, mean generation time and doubling time of treated insects was significantly longer than control at LC10 level. Therefore, the data from this study suggested that fenoxycarb could adversely cause population decline in the subsequent generation.

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.

Deciphering the metabolic changes associated with diapause syndrome and cold acclimation in the two-spotted spider mite Tetranychus urticae

Diapause is a common feature in several arthropod species that are subject to unfavorable growing seasons. The range of environmental cues that trigger the onset and termination of diapause, in addition to associated hormonal, biochemical, and molecular changes, have been studied extensively in recent years; however, such information is only available for a few insect species. Diapause and cold hardening usually occur together in overwintering arthropods, and can be characterized by recording changes to the wealth of molecules present in the tissue, hemolymph, or whole body of organisms. Recent technological advances, such as high throughput screening and quantification of metabolites via chromatographic analyses, are able to identify such molecules. In the present work, we examined the survival ability of diapausing and non-diapausing females of the two-spotted spider mite, Tetranychus urticae, in the presence (0 or 5°C) or absence of cold acclimation. Furthermore, we examined the metabolic fingerprints of these specimens via gas chromatography-mass spectrophotometry (GC-MS). Partial Least Square Discriminant Analysis (PLS-DA) of metabolites revealed that major metabolic variations were related to diapause, indicating in a clear cut-off between diapausing and non-diapausing females, regardless of acclimation state. Signs of metabolic depression were evident in diapausing females, with most amino acids and TCA cycle intermediates being significantly reduced. Out of the 40 accurately quantified metabolites, seven metabolites remained elevated or were accumulated in diapausing mites, i.e. cadaverine, gluconolactone, glucose, inositol, maltose, mannitol and sorbitol. The capacity to accumulate winter polyols during cold-acclimation was restricted to diapausing females. We conclude that the induction of increased cold hardiness in this species is associated with the diapause syndrome, rather than being a direct effect of low temperature. Our results provide novel information about biochemical events related to the cold hardening process in the two-spotted spider mite.

Effect of milk thistle, Silybium marianum, extract on toxicity, development, nutrition, and enzyme activities of the small white butterfly, Pieris rapae

The methanolic extract of milk thistle, Silybium marianum L. (Asterales: Asteraceae), was investigated for its effects on the mortality, growth, feeding indices, enzymatic activity, and levels of non-enzymatic molecules of the small white butterfly, Pieris rapae L. (Lepidoptera: Pieridae), a pest of cruciferous plants. Feeding indices including approximate digestibility (AD), efficiency of conversion of digested food (ECD), efficiency of conversion of ingested food (ECI), relative growth rate (RGR), and relative consumption rate (RCR) were measured. These indices were variously affected: the RGR, RCR, and AD decreased, but the ECD and ECI increased. The LC50 and LC25 values were estimated as 2.94% and 1.20%, respectively. At the lowest concentration of S. marianum extract (0.625%), the feeding deterrence index was 40.48%. The duration of the pupal stage and the rate of larval growth decreased. These changes may be due to alterations in metabolic activity, such as the increase in alkaline phosphatase activity, which is likely involved in detoxification. Additionally, the activities of alanine aminotransferase and aspartate aminotransferase, which are key components of amino acid catabolism, decreased. The amount of glucose (an energy source) and uric acid (the excreted end product) increased, while total protein (another energy source) and cholesterol decreased. These results indicate that this plant possesses potential secondary metabolites that may be useful for the future study of the control of insect pests.

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.

Demographic parameters of Spodoptera exigua (Lepidoptera: Noctuidae) on different soybean cultivars

Life table, reproduction, and population growth parameters of the beet armyworm, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae), were determined on nine soybean (Glycine max L.) cultivars ('032', '033', 'Hill', 'M4', 'M7', 'M9', 'M11', 'TMS', and 'Zane') at 25°C. The age-specific survival rate of eggs and immature stages was higher on 033 in comparison with other cultivars. The gross fecundity rate ranged from 911 on M9 to 1,296 on Zane, but the differences were not statistically significant. The net fecundity rate was significantly higher on 033 (1,082 eggs per female) than on other cultivars. The gross fertility rate significantly differed on tested cultivars, and was the highest on Zane (1,257 eggs per female) and lowest on Hill (813 eggs per female). The net fertility rate varied from 532 on M11 to 1,082 eggs per female on 033. Both daily number of eggs and daily number of fertile eggs laid per female varied significantly among the different cultivars, and were the highest on TMS (90 for both parameter) and lowest on M7 (47 and 43), respectively. The values of net reproductive rate, intrinsic rate of increase, and finite rate of increase were significantly higher on 033. The shortest generation time (23 d), shortest doubling time (1.66 d), and highest percentage of female offspring (56%) also were obtained on 033. According to population growth parameters, 033 and Hill partially were susceptible and resistant, respectively, to S. exigua. The results of this study provide direction to design a more comprehensive integrated pest management program for this pest.

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.

Biological activity of some plant essential oils against Varroa destructor (Acari: Varroidae), an ectoparasitic mite of Apis mellifera (Hymenoptera: Apidae)

This experiment was conducted to evaluate acaricidal activity of the essential oils of Thymus kotschyanus, Ferula assa-foetida and Eucalyptus camaldulensis against Varroa destructor under laboratory conditions. Moreover, fumigant toxicity of these oils was tested on Apis mellifera. After preliminary dose-setting experiments, mites and honey bees were exposed to different concentrations of the oil, with 10 h exposure time. Essential oil of T. kotschyanus appeared the most potent fumigant for V. destructor (LC(50) = 1.07, 95% confidence limit (CL) = 0.87-1.26 μl/l air), followed by E. camaldulensis (LC(50) = 1.74, 95% CL = 0.96-2.50 μl/l air). The lowest acaricidal activity (LC(50) = 2.46, 95% CL = 2.10-2.86 μl/l air) was attributed to essential oil of F. assa-foetida. Surprisingly, among the three oils tested, essential oil of T. kotschyanus had the lowest insecticidal activity against A. mellifera (LC(50) = 5.08, 95% CL = 4.54-5.06 μl/l air). These findings proved that essential oil of T. kotschyanus has potential of practical value for use as alternative acaricide in the management of varroa in apiaries.

Digestive proteolytic and amylolytic activities of Helicoverpa armigera in response to feeding on different soybean cultivars

BACKGROUND

Digestive proteolytic and amylolytic activities of the larvae of Helicoverpa armigera (Hübner) fed either on artificial diet or on different soybean cultivars (356, M4, M7, M9, Clark, Sahar, JK, BP, Williams, L17, Zane, Gorgan3 and DPX) and response of the larvae to feeding on some soybean-based protease inhibitors were studied.

RESULTS

The highest general and specific proteolytic activities were in artificial-diet-fed larvae. Although the highest general proteolytic activity was in the larvae fed on L17, M4 and Sahar cultivars, the lowest tryptic activity was on L17 and Sahar, which may be due to the presence of some serine protease inhibitors in these two cultivars, resulting in hyperproduction of chymotrypsin- and elastase-like enzymes in response to the inhibition of these enzymes. The highest amylolytic activity was on M4, and the lowest was on Williams and DPX. General proteolytic activity of SKTI-fed larvae was the highest compared with SBBI- and STI-fed larvae.

CONCLUSION

The findings demonstrated that the cultivars L17 and Sahar were partially resistant to this pest, probably because of some secondary chemicals or proteinaceous protease inhibitors of these cultivars.

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.

Evaluation of potential resistance in seeds of different soybean cultivars to Helicoverpa armigera (Lepidoptera: Noctuidae) using demographic parameters and nutritional indices

The use of resistant cultivars is a key component of any integrated pest management (IPM) program. Here, we assess the resistance status of 10 different soybean cultivar seeds according to their effects on demographic and nutritional indices of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) when incorporated into artificial diets. All experiments were conducted at 25 +/- 1 degrees C, 60 +/- 5% RH, and a photoperiod of 16:8 (L:D) h. Life table, reproduction, development, adult longevity, and nutritional indices of H. armigera were significantly affected by the cultivars examined. Mean developmental time of across all immature stages varied from 57 d on 'L17' to 32 d on 'Clark'. Efficiency of conversion of digested food (ECD) for old larvae ranged from 36.4% on 'Sari' to 14.8% on 'Sahar'. The adults that emerged from these larvae had very different rates of reproduction; the highest and lowest values for net reproductive rate (Ro) were 270 and 17 on Clark and L17, respectively. The most important demographic parameter, intrinsic rate of increase (rm), ranged from 0.114 on Sari to 0.09 on L17. H. armigera did not perform well on Sahar, L17, 'Gorgan3', and 'M4'. These cultivars show antibiosis resistance compared with other tested cultivars and are key candidates for field tests to determine usefulness in an IPM system.

Modeling demographic response to constant temperature in Hypera postica (Coleoptera: Curculionidae)

Alfalfa weevil, Hypera postica (Gyllenhal) (Coleoptera: Curculionidae), is among the most destructive pests of alfalfa, Medicago sativa L., in the world. Survivorship and fecundity schedules of H. postica were investigated to characterize the population growth potential of the weevil at six constant temperatures: 11.5, 14.0, 19.0, 24.0, 29.0, and 31.5 degrees C. Preoviposition period, oviposition period and female longevity significantly decreased with rising temperature within the temperature range tested. At the respective temperatures adult female lived an average of 294.2, 230.2, 163.6, 141.0, 84.10, and 32.9 d, with average lifetime progeny production of 470, 814, 2209, 3619, 2656, and 338 eggs per female. The net reproductive rates (R0) were 86.9, 288.0, 869.7, 1,479.7, 989.8, and 107.8 females per female, respectively. Mean daily fecundity (Mx) was modeled as a function of time by using both Enkegaard and Analytis models. Survivorship data (l(x)) of adult females were summarized and compared using the shape and scale parameters of the Weibull frequency distribution model across the temperature range tested. Life table entropy values within the range 14.0-31.5 degrees C (H < 0.5) indicates Slobodkin's type I survivorship curve; however, the value of 0.806 at 11.5 degrees C (H > 0.5) corresponds to type III. As temperature increased, the r(m) exhibited an asymmetrical dome-shaped pattern, with a maximum value of 0.114 females per female per d at 29.0 degrees C. The r(m)-temperature relation of weevils was modeled and critical temperatures (T(Min), T(Opt), and T(Max)) for intrinsic rate of increase of the weevil were computed as 8.83, 30.61, and 32.14 degrees C and 5.72, 29.94, and 32.12 degrees C by using Analytis/Allahyari and Analytis/Briere-2 models, respectively.

Preimaginal development response to constant temperatures in Hypera postica (Coleoptera: Curculionidae): picking the best model

Immature survival and development of alfalfa weevil, Hypera postica (Gyllenhal) (Coleoptera: Curculionidae), were examined at 15 constant temperatures ranging from 9 to 37 degrees C. At 9 and 37 degrees C, eggs did not develop. Embryos developed to adulthood between 11.5 and 36 degrees C, although survival was low at both ends of the temperature range. Distribution of development times for all stages of alfalfa weevil were skewed toward longer times mainly at moderate temperatures. Constant proportion of time spent in egg, larva, and pupa indicated rate isomorphy within the range 14-31.5 degrees C. No significant difference was shown between development time of males and females at any of the temperatures tested. Two linear and 23 nonlinear models were fitted to describe development rate of immature stages of H. postica as a function of temperature, as well as estimating the thermal constant and critical temperatures (i.e., T(min), T(opt), and T(max)). There was no statistical difference between the estimated parameters, using Ikemoto and ordinary linear methods. Of the nonlinear models fitted, the Logan-6/Lactin-2, Analytis-3/Briere-2, and Analytis-3/Briere-2 models were found to be the best for modeling development rate of egg, larva, and entire immature stages of H. postica, respectively. Our findings will be incorporated in more efficient phenological models of this pest and its population dynamics.

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.

Cold hardiness and supercooling capacity in the overwintering larvae of the codling moth, Cydia pomonella

The codling moth, Cydia pomonella L. (Lepidoptera: Tortricidae), a worldwide apple pest, is classified as a freeze-intolerant organism and one of the most cold-tolerant pests. The objectives of this study were to examine the supercooling point of overwintering and non-diapausing larvae of C. pomonella as an index of its cold hardiness, and to assess larval mortality following 24 h exposure to extreme low temperatures ranging from -5 to -25 degrees C. The mean (+/-SE) supercooling point for feeding larvae (third through fifth instars) was -12.4 +/- 1.1 degrees C. The mean supercooling point for cocooned, non-diapausing larvae (i.e., non-feeding stages) decreased as the days that the arvae were cocooned increased and changed between -15.1 +/- 1.2 degrees C for one to two day cocooned arvae and -19.2 +/- 1.8 degrees C for less than five day cocooned larvae. The mean (+/-SE) supercooling point for other non-feeding stages containing pupae and overwintering larvae were -19.9 +/- 1.0 degrees C and -20.2 +/- 0.2 degrees C, respectively. Mean supercooling points of C. pomonella larvae were significantly lower during the winter months than the summer months, and sex had no effect on the supercooling point of C. pomonella larvae. The mortality of larvae increased significantly after individuals were exposed to temperatures below the mean supercooling point of the population. The supercooling point was a good predictor of cold hardiness.

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.

Seasonal change of cold hardiness in the codling moth, Cydia pomonella (Lepidoptera: Tortricidae)

To elucidate the relationship between diapause and cold hardiness, seasonal variations of supercooling point and low temperature survival of overwintering and non-diapausing larvae of codling moth were studied in two regions of Iran, Damavand and Karaj. In both regions supercooling point decreased gradually over the autumn. Supercooling point of field collected larvae in Damavand reduced from a mean value of -16.9 degrees C in early September to -19.9 degrees C in mid-October 2004. At the same time, supercooling point of overwintering larvae decreased from -19 to -21 degrees C in Karaj. Supercooling point decreased gradually until midwinter (January) in both regions and afterward increased gradually over the spring. Mean supercooling point for non-diapausing larvae was -13.4 degrees C, which was significantly higher than that of overwintering larvae. A high coincidence was observed between decrease of supercooling point and increase of low temperature survival rate in the overwintering larvae. Survival rate at -20 degrees C/24 h was lower than 20% in early autumn; that increased to upper than 50% during winter. Codling moth was shown to be a freeze susceptible and at the same time, a chill tolerant insect.

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.

Effect of cotton cultivar on performance of Aphis gossypii (Homoptera: Aphididae) in Iran

Cotton aphids, Aphis gossypii Glover (Homoptera: Aphididae), obtained from cotton, Gossypium hirsutum L., fields in the Gorgan region of northern Iran, were colonized on 'Varamin' cotton plants in a growth chamber. The development, survivorship, and life table parameters of the cotton aphid were evaluated at 27.5 +/- 1 degrees C, 65 +/- 10% RH, and aphotoperiod of 14:10 (L:D) h of artificial light on five commonly growing cotton cultivars: Varamin, 'Sealand' (relatively resistant cultivar), 'Bakhtegan', 'Sahel' (both relatively susceptible cultivars), and 'Siokra' [resistant to Bemisia tabaci (Gennadius)]. The developmental times of immature stages ranged from 4.6 d on Bakhtegan and Varamin to 6.3 d on Sealand, whereas the immature survival was 97.5 to 65% on Sahel and Siokra, respectively. On average, there were 28.7, 28.3, 23.5, 20.1, and 16.8 nymphs produced per female on Sahel, Bakhtegan, Varamin, Sealand, and Siokra, respectively. The intrinsic rate of natural increase (r(m)) for cotton aphids on Sahel was the highest, whereas the values for r(m) varied from 0.284 (nymphs per female per d) on Siokra to 0.368 on Sahel. Jackknife estimates of generation times (T), net reproductive rate (R(0)), doubling time (DT), and finite rate of increase (lambda) on these cultivars were as follows: 9.79-10.84 d for T, 9.23-23.81 nymphs per female for R(0), 2.17-3.19 d for DT, and 1.28-1.38 nymphs per female per d for lambda. Cotton aphid performance was at its highest on Sahel and lowest on Siokra.

Lethal and sublethal effects of fenitrothion and deltamethrin residues on the egg parasitoid Trissolcus grandis (Hymenoptera: Scelionidae)

Effects of fenitrothion and deltamethrin, the most commonly used insecticides in Iran for controlling Eurygaster integriceps Puton (Heteroptera: Scutelleridae), in wheat and barley were assessed on adults and preimaginal stages of egg parasitoid Trissolcus grandis Thompson (Hymenoptera: Scelionidae). Adult parasitoids exposed to field recommended concentrations of the insecticides suffered 100% mortality within 24 h. LC50 values of fenitrothion and deltamethrin for T. grandis were 8.1 and 3.9 microg (AI) /ml, respectively. Both insecticides and the preimaginal stage of exposure had a significant influence on the level of adult emergence from host eggs treated with field recommended rates. Fenitrothion and deltamethrin reduced the emergence rates by 18 and 34.4%, respectively, compared with the control. However, neither insecticide significantly affected the longevity or reproductive capacity of emerged females, or the sex ratio of their progeny. This study revealed that application of these insecticides should be avoided in early season to conserve natural or released populations of T. grandis. Both insecticides seemed to be detrimental to the parasitoid and need to be applied cautiously through season.