Identification and characterization of the pyrokinin/pheromone biosynthesis activating neuropeptide family of G protein-coupled receptors from Ostrinia nubilalis

Insects have two closely related G protein-coupled receptors belonging to the pyrokinin/pheromone biosynthesis activating neuropeptide (pyrokinin/PBAN) family, one with the ligand PBAN or pyrokinin-2 and another with diapause hormone or pyrokinin-1 as a ligand. A related receptor is activated by products of the capa gene, periviscerokinins. Here we characterized the PBAN receptor and the diapause hormone receptor from the European corn borer, Ostrinia nubilalis. We also identified a partial sequence for the periviscerokinin receptor. Quantitative PCR of mRNA for all three receptors indicated differential expression in various life stages and tissues. All three splice variants of the PBAN receptor were identified with all variants found in pheromone gland tissue. Immunohistochemistry of V5 tags of expressed receptors indicated that all three variants and the diapause hormone receptor were expressed at similar levels in Spodoptera frugiperda 9 (Sf9) cells. However, the A- and B-variants were not active in our functional assay, which confirms studies from other moths. Functional expression of the C-variant indicated that it is has a 44 nM half effective concentration for activation by PBAN. The diapause hormone receptor was activated by diapause hormone with a 150 nM half effective concentration.

Four serine protease cDNAs from the midgut of Plutella xylostella and their proteinase activity are influenced by the endoparasitoid, cotesia vestalis

Serine proteinases, which include trypsins and chymotrypsins, play numerous roles in lepidopteran larvae, such as digestion, zymogen activation, and immune defense. Studies of lepidopteran serine proteinases could increase understanding of their feeding preference (polyphagous and monophagous) and facilitate identification of protease inhibitors, which can be engineered for pest management. In this paper, four full-length cDNAs encoding one chymotrypsin and three trypsins were cloned from larval midguts of the diamondback moth, Plutella xylostella. Real-time quantitative polymerase chain reaction (PCR) analysis showed all four serine protease genes were downregulated after P. xylostella was parasitized by the parasitoid wasp Cotesia vestalis. Trypsin and chymotrypsin enzymatic activities within the midgut of nonparasitized and C. vestalis-parasitized P. xylostella larvae were examined using N-a-benzoyl-arg p-nitroanilide and N-succinyl-ala-ala-pro-phe p-nitroanilide as substrates. Trypsin and chymotrypsin activities were decreased in parasitized larvae as compared to untreated larvae, with the effect being more pronounced over time. Chymotrypsin activity in particular exhibited a significant decrease in activity. The correlation of decreased enzymatic activity and transcript abundance suggests parasitization induced downregulation of serine proteinase gene transcripts.

Western bean cutworm survival and the development of economic injury levels and economic thresholds in field corn

Western bean cutworm, Striacosta albicosta (Smith) (Lepidoptera: Noctuidae), is a native pest of dry beans (Phaseolus vulgaris L.) and corn (Zea mays L.). Historically, the western bean cutworm was distributed in the western United States, but since 1999 eastward expansion has been observed. In corn, economic impact is caused by larval ear feeding. Information on western bean cutworm biology, ecology, and economic impact is relatively limited, and the development of economic injury levels (EILs) and economic thresholds (ETs) is required for more effective management. Studies during 2008-2011, across three ecoregions of Nebraska, sought to characterize western bean cutworm survival and development of EILs and ETs. Calculations of EILs and ETs incorporated the dynamics of corn price, management cost, and pest survival. The results from the current study demonstrated low larval survival of this species (1.51-12.82%). The mean yield loss from one western bean cutworm larva per plant was 945.52 kg/ha (15.08 bu/acre), based on 74,100 plants per ha. Economic thresholds are expressed as a percentage of plants with at least one egg mass. This study is the first study that explicitly incorporates variable management costs and crop values into western bean cutworm EIL calculations, and larval survival into ET calculations.

Direct and indirect effects of the synthetic-auxin herbicide dicamba on two lepidopteran species

Herbicides are the most commonly applied pesticides in agroecosystems, and therefore pose potentially significant ecotoxicological risks to plants and insects. Glyphosate is the most common herbicide worldwide, and glyphosate-resistant weeds are quickly becoming serious challenges in some agroecosystems. Because of this resistance epidemic and the recent development of crops with resistance to dicamba or 2,4-D, herbicide-use patterns are likely to change. Presently, dicamba and 2,4-D cause most herbicide-drift damage to nontarget plants despite limited agricultural usage, but the effects of these synthetic auxin herbicides on insects have been poorly explored. To understand the influence of dicamba on insects, we applied several sublethal, drift-level rates of dicamba to soybean, Glycine max L., and Carduus thistle, and measured growth and survival of Helicoverpa zea (Boddie) and Vanessa cardui (L.) larvae, respectively. For thistle, we measured percent nitrogen content before and after dicamba application. We also performed direct toxicity bioassays on the two caterpillar species with several rates of dicamba. Dicamba was not directly toxic to larvae of either species, and H. zea showed no negative effects when feeding on soybeans dosed with dicamba. We did, however, detect significant negative, indirect effects of higher rates of dicamba on V. cardui larval and pupal mass, total nitrogen of thistles post application, and thistle biomass in the presence of V. cardui larvae. Notably, thistle biomass was not related to dicamba dose in absence of larvae. Our results indicate that dicamba can indirectly influence the performance of some caterpillar species, possibly by altering plant nutritional content.

High expression of PP2A-Aα is associated with diapause induction during the photoperiod-sensitive stage of the cotton bollworm, Helicoverpa armigera

Protein phosphatase 2A (PP2A) is a major serine-threonine protein phosphatase which regulates metabolism, transcription, RNA splicing, translation, differentiation, cell cycle, oncogenic transformation and signal transduction. PP2A-Aα, an isoform of PP2A-A, is a structural subunit of the PP2A complex. We identified the photoperiod-sensitive stage for pupal diapause induction to be from the fifth instar to the early sixth instar larvae in the cotton bollworm, Helicoverpa armigera. PP2A-Aα cDNA from brains of diapause-destined fifth instar larvae was obtained by suppressive subtractive hybridization using nondiapause-destined larval brains as a control. Developmental expression of PP2A-Aα mRNA during the photoperiod-sensitive stage was higher in brains of diapause-destined larvae, and the PP2A-Aα protein showed a similar expression pattern as the mRNA. When larvae were transferred from diapause-inducing short days to long days during the diapause-sensitive stage, both PP2A-Aα mRNA and protein decreased significantly, and diapause incidence was also reduced. Thus, high PP2A-Aα expression during the diapause-sensitive stage may play a crucial role in photoperiodic induction of diapause, suggesting that it may be a new player involved in the molecular mechanism for diapause induction.

[Effect of total ginsenoside on content of protein and activity of digestive enzyme of Mythimna separata larvae]

OBJECTIVE

This study aims to reveal the effect of total ginsenoside on the protein content and digestive enzyme activities of 4th-instar Mythimna separata larvae, including alpha-amylase and cellulose, and explore the ecological function of total ginsenoside.

METHOD

While simulating natural growing condition indoors, 4th-instar M. separata larvae were fed by poison leaf disk method. The protein content was tested by Lowry Protein Assay Kit method, the activity of alpha-amylase was measured by dinitrosalicylic acid test, and the activity of cellulase was determined by the filter paper method.

RESULT

The total ginsenoside could reduce the content of protein of 4th-instar M. separata larvae significantly, and the activity of digestive enzyme, including alpha-amylase and cellulase. The protein content, alpha-amylase and cellulase activity of treatments were obviously lower than that of the control. Inhibition ratio of alpha-amylase and cellulase activity was positively correlated with total ginsenoside concentration: i. e. 20 g x L(-1) > 10 g x L(-1) > 5 g x L(-1).

CONCLUSION

The results suggest that the inhibition effect of total ginsenoside on protein content and digestive enzymes may be one of the causes to antifeedant and dysplasia of M. separata larvae.

Baseline toxicity of metaflumizone and lack of cross resistance between indoxacarb and metaflumizone in diamondback moth (Lepidoptera: Plutellidae)

Diamondback moth, Plutella xylostella (L.) is a serious insect pest of vegetables worldwide, and has evolved resistance to various kinds of insecticides. Studies were conducted to determine the baseline toxicity of metaflumizone and the possibility of cross-resistance between metaflumizone and indoxacarb, two sodium channel blocking insecticides (SCBIs), in field populations of P. xylostella from China. The variation in susceptibility to metaflumizone among 29 field populations of P. xylostella collected from 14 geographical locations in China was less than five-fold, with 50% lethal concentrations (LC50(s)) varying from 1.34 to 6.55 mg/liter. Limited variations in LC50(s) (less than five-fold, ranging from 1.76 to 8.16 mg/liter) were also observed in the four laboratory-selected strains with high levels of resistance to abamectin, spinosad, fipronil, or Bt toxin Cry1Ac. The toxicity of metaflumizone and indoxacarb was compared among 23 out of the 29 field populations. When compared with the susceptible Roth strain, the JN-09B population showed the highest level of resistance to indoxacarb (110-fold), but two-fold tolerance to metaflumizone. The other 22 populations (with 5- to 58-fold of resistance to indoxacarb) had 1- to three-fold tolerance to metaflumizone. Metaflumizone could provide an effective alternative insecticide for diamondback moth management. Although the field populations of P. xylostella tested with various levels of resistance to indoxacarb did not have cross-resistance to metaflumizone, metaflumizone should be rotated with other chemicals of different modes of action instead of indoxacarb.

Relationship of almond kernel damage occurrence to navel orangeworm (Lepidoptera: Pyralidae) success

ALaboratory and field studies are reported that assess navel orangeworm (Amyelois transitella (Walker)) development and damage on 11 almond varieties that represent both expected and outlying hull split and shell seal A. transitella damage. Twenty neonate larvae were introduced to almonds of three treatments for each variety: scratched (1 mm scratch through the pellicle), shelled (shell removed but pellicle intact), and unshelled (shell intact and exhibiting the tightest shell seal for the variety). Success was evaluated as moth emergence and degree-days (DD) to emergence. In 2010-2011 and 2011-2012, 10 replicate rows containing randomized strands of 20 unshelled, uninfested almonds from each variety were placed in the field for both the fall and spring A. transitella flight. The almonds were returned to the lab before the initiation of the second spring A. transitella flight and categorized by presumed cause of damage (bird damage, A. transitella damage, or both types of damage). Damage, variety, and their interaction significantly impacted A. transitella survival and DDs to emergence in male moths. Female moth DDs to emergence were significantly impacted by damage alone. Damage from birds and A. transitella damage were positively correlated, and A. transitella damage associated with bird damage was more common than A. transitella damage alone. Nonconspecific damage may have a significant impact on A. transitella populations in the field, and bird damage may have repercussions beyond its direct impact on marketable yield.

Differential protease activity augments polyphagy in Helicoverpa armigera

Helicoverpa armigera (Lepidoptera: Noctuidae) and other polyphagous agricultural pests are extending their plant host range and emerging as serious agents in restraining crop productivity. Dynamic regulation, coupled with a diversity of digestive and detoxifying enzymes, play a crucial role in the adaptation of polyphagous insects. To investigate the functional intricacy of serine proteases in the development and polyphagy of H. armigera, we profiled the expression of eight trypsin-like and four chymotrypsin-like phylogenetically diverse mRNAs from different life stages of H. armigera reared on nutritionally distinct host plants. These analyses revealed diet- and stage-specific protease expression patterns. The trypsins expressed showed structural variations, which might result in differential substrate specificity and interaction with inhibitors. Protease profiles in the presence of inhibitors and their mass spectrometric analyses revealed insight into their differential activity. These findings emphasize the differential expression of serine proteases and their consequences for digestive physiology in promoting polyphagy in H. armigera.

Interactive direct and plant-mediated effects of elevated atmospheric [CO2 ] and temperature on a eucalypt-feeding insect herbivore

Understanding the direct and indirect effects of elevated [CO2 ] and temperature on insect herbivores and how these factors interact are essential to predict ecosystem-level responses to climate change scenarios. In three concurrent glasshouse experiments, we measured both the individual and interactive effects of elevated [CO2 ] and temperature on foliar quality. We also assessed the interactions between their direct and plant-mediated effects on the development of an insect herbivore of eucalypts. Eucalyptus tereticornis saplings were grown at ambient or elevated [CO2 ] (400 and 650 μmol mol(-1) respectively) and ambient or elevated ( + 4 °C) temperature for 10 months. Doratifera quadriguttata (Lepidoptera: Limacodidae) larvae were feeding directly on these trees, on their excised leaves in a separate glasshouse, or on excised field-grown leaves within the temperature and [CO2 ] controlled glasshouse. To allow insect gender to be determined and to ensure that any sex-specific developmental differences could be distinguished from treatment effects, insect development time and consumption were measured from egg hatch to pupation. No direct [CO2 ] effects on insects were observed. Elevated temperature accelerated larval development, but did not affect leaf consumption. Elevated [CO2 ] and temperature independently reduced foliar quality, slowing larval development and increasing consumption. Simultaneously increasing both [CO2 ] and temperature reduced these shifts in foliar quality, and negative effects on larval performance were subsequently ameliorated. Negative nutritional effects of elevated [CO2 ] and temperature were also independently outweighed by the direct positive effect of elevated temperature on larvae. Rising [CO2 ] and temperature are thus predicted to have interactive effects on foliar quality that affect eucalypt-feeding insects. However, the ecological consequences of these interactions will depend on the magnitude of concurrent temperature rise and its direct effects on insect physiology and feeding behaviour.

Silencing the HaHR3 gene by transgenic plant-mediated RNAi to disrupt Helicoverpa armigera development

RNA interference (RNAi) caused by exogenous double-stranded RNA (dsRNA) has developed into a powerful technique in functional genomics, and to date it is widely used to down-regulate crucial physiology-related genes to control pest insects. A molt-regulating transcription factor gene, HaHR3, of cotton bollworm (Helicoverpa armigera) was selected as the target gene. Four different fragments covering the coding sequence (CDS) of HaHR3 were cloned into vector L4440 to express dsRNAs in Escherichia coli. The most effective silencing fragment was then cloned into a plant over-expression vector to express a hairpin RNA (hpRNA) in transgenic tobacco (Nicotiana tabacum). When H. armigera larvae were fed the E. coli or transgenic plants, the HaHR3 mRNA and protein levels dramatically decreased, resulting developmental deformity and larval lethality. The results demonstrate that both recombinant bacteria and transgenic plants could induce HaHR3 silence to disrupt H. armigera development, transgenic plant-mediated RNAi is emerging as a powerful approach for controlling insect pests.

Prothoracicotropic hormone acts as a neuroendocrine switch between pupal diapause and adult development

Diapause is a programmed developmental arrest that has evolved in a wide variety of organisms and allows them survive unfavorable seasons. This developmental state is particularly common in insects. Based on circumstantial evidence, pupal diapause has been hypothesized to result from a cessation of prothoracicotropic hormone (PTTH) secretion from the brain. Here, we provide direct evidence for this classical hypothesis by determining both the PTTH titer in the hemolymph and the PTTH content in the brain of diapause pupae in the cabbage army moth Mamestra brassicae. For this purpose, we cloned the PTTH gene, produced PTTH-specific antibodies, and developed a highly sensitive immunoassay for PTTH. While the hemolymph PTTH titer in non-diapause pupae was maintained at high levels after pupation, the titer in diapause pupae dropped to an undetectable level. In contrast, the PTTH content of the post-pupation brain was higher in diapause animals than in non-diapause animals. These results clearly demonstrate that diapause pupae have sufficient PTTH in their brain, but they do not release it into the hemolymph. Injecting PTTH into diapause pupae immediately after pupation induced adult development, showing that a lack of PTTH is a necessary and sufficient condition for inducing pupal diapause. Most interestingly, in diapause-destined larvae, lower hemolymph titers of PTTH and reduced PTTH gene expression were observed for 4 and 2 days, respectively, prior to pupation. This discovery demonstrates that the diapause program is already manifested in the PTTH neurons as early as the mid final instar stage.

First report of Endoclita signifer (Lepidoptera: Hepialidae) as a new pest on Eucalyptus

Endoclita signifier Walker (Lepidoptera: Hepialidae) has become a new wood borer pest in Eucalyptus plantations in southern China. This article documents survey results of its geographic distribution and host plant range in Guangxi and its morphological measurements, life cycle and behavior. In total, 83 Eucalyptus growing counties were surveyed. E. signifier was found in 59 counties. Host plants included 31 species in 16 families and 24 genera. Four Eucalyptus hybrid species were recorded as its host plant with E. grandis x E. urophylla and E. urophylla x E. grandis infested the heaviest. The infestation of Eucalyptus trees 1-2 yr old was heavier than that of older trees. Most individuals of E. signifier took 1 yr to complete a generation, overwintering as larvae in tunnels in wooden stems, and pupating in February of the following year. Adults emerge, mate, and lay eggs in April, and the eggs hatch in late April or early May. Adult emergence peaks between 17:00-18:59 hours. Mating flights last under 30 min at dusk and the copulation duration was 24 h. Moths were large, weighting and average of 3.4 g. Eggs and newly hatched larvae were very small, weighing only 0.127 +/- 0.001 mg and 0.093 +/- 0.017 mg, respectively. The larvae have two distinct development stages. One stage spends 1-2 mo living in the forest litter, the second stage then moves to woody stems where it feeds for approximately 10 mo. Larvae start boring into hosts between June and November, mainly in July and August. This study indicated that E. signifier, a highly polyphagous native species, has shifted host to exotic Eucalyptus and can cause significant damage to plantations.

Steroid hormone 20-hydroxyecdysone regulation of the very-high-density lipoprotein (VHDL) receptor phosphorylation for VHDL uptake

During the metamorphic stage of holometabolous insects, the biosynthetic precursors needed for the synthesis of a large number of adult proteins are acquired from the selective absorption of storage proteins. The very-high-density lipoprotein (VHDL), a non-hexameric storage protein, is consumed by the fat body from the hemolymph through VHDL receptor (VHDL-R)-mediated endocytosis. However, the mechanism of the uptake of VHDL by a VHDL-R remains unclear. In this study, a VHDL-R from Helicoverpa armigera was found to be involved in 20E-regulated VHDL uptake through the regulation of steroid hormone 20-hydroxyecdysone (20E). The transcripts of VHDL-R were detected mainly in the fat body and integument during the wandering stage. The transcription of VHDL-R was upregulated by 20E through the ecdysteroid receptor (EcRB1) and Ultraspiracle (USP1). In addition, 20E stimulates the phosphorylation of VHDL-R through protein kinase C for ligand binding. VHDL-R knockdown in larvae results the inhibition of development to adulthood. These data imply that 20E regulates VHDL-R on both transcriptional and posttranslational levels for VHDL absorption.

The case for a generic phytosanitary irradiation dose of 400 Gy for Lepidoptera that infest shipped commodities as pupae

The pros and cons of a generic phytosanitary irradiation dose against all Lepidoptera pupae on all commodities are discussed. The measure of efficacy is to prevent the F1 generation from hatching (F1 egg hatch) when late pupae are irradiated. More data exist for this measure than for others studied, and it is also commercially tenable (i.e., prevention of adult emergence would require a high dose not tolerated by fresh commodities). The dose required to prevent F1 egg hatch provides a liberal margin of security for various reasons. A point at issue is that correctly irradiated adults could be capable of flight and thus be found in survey traps in importing countries resulting in costly and unnecessary regulatory action. However, this possibility would be rare and should not be a barrier to the adoption of this generic treatment. The literature was thoroughly examined and only studies that could reasonably satisfy criteria of acceptable irradiation and evaluation methodology, proper age of pupae, and adequate presentation of raw data were accepted. Based on studies with 34 species in nine families, we suggest an efficacious dose of 400 Gy. However, large-scale confirmatory testing (> or = 30,000 individuals) has only been reported for one species. A dose as low as 350 Gy might suffice if results of more large-scale studies were available or the measure of efficacy were extended beyond prevention of F1 egg hatch, but data to defend measures of efficacy beyond F1 egg hatch are scarce and more would need to be generated.

Identification of microRNAs from Plutella xylostella larvae associated with parasitization by Diadegma semiclausum

MicroRNAs (miRNAs) as small non-coding RNAs play important roles in many biological processes such as development, cell signaling and immune response. Small RNA deep sequencing technology provided an opportunity for a thorough survey of miRNAs in a global key pest Plutella xylostella as well as comparative analysis of miRNA expression profile of the insect in association with parasitization by Diadegma semiclausum. Combining the deep sequencing data and bioinformatics, 235 miRNAs were identified from P. xylostella. Differential expression of host cellular miRNAs in response to parasitism was examined by making small RNA libraries from parasitized and naive second instar larvae of P. xylostella. Bantam, miR-276*, miR-10, miR-31 and miR-184 were detected as five most abundant miRNAs in both libraries and 96 miRNAs were identified that were differentially expressed after parasitization. Bantam*, miR-184 and miR-281* were significantly down-regulated and two miRNAs miR-279b and miR-2944b* were highly induced in parasitized larvae. Interestingly, high copy numbers and differential expression of several miRNA passenger strands (miRNA*) suggest their potential roles in host-parasitoid interaction. In conclusion, expression profiling of miRNAs provided insights into their possible involvement in insect immune response to parasitism and offer an important resource for further studies.

Segregation and efficacy of the cry1Ia1 gene for control of potato tuberworm in four populations of cultivated potato

The potato (Solanum tuberosum L.) cultivar 'SpuntaG2' contains a single copy of the Bacillus thuringiensis (Bt) cry1Ia1 gene and controls potato tuberworm (Phthorimaea operculella Zeller, Lepidoptera: Gelechiidae). Two potato cultivars and two breeding lines were crossed with SpuntaG2 creating four populations used to study cry1Ia1 segregation and efficacy. The cry1Ia1 gene segregated in each of the four populations with a 1:1 ratio. All progeny that were polymerase chain reaction positive for the cry1Ia1 gene had no surviving larvae and no leaf mining in detached leaf assays after 72 h. These results support previous evidence that SpuntaG2 carries a single copy of the cry1Ia1 gene and that transmission of the transgene from parent to progeny is not restricted and follows expected Mendelian segregation ratios. Based on detached leaf assays, the efficacy of the cry1Ia1 gene is retained through sexual transmission. If the SpuntaG2 cry1Ia1 insertion event is deregulated for commercial use, SpuntaG2 could be used for conventional breeding and the progeny carrying the SpuntaG2 event would also be available for commercial use.

Demography and randomized life table statistics for peach twig borer Anarsia lineatella (Lepidoptera: Gelechiidae)

This work studies for first time the effect of constant temperatures (15, 20, 25, 30 and 3 degrees C) on the demography of Anarsia lineatella Zeller (Lepidoptera: Gelechiidae) based on jackknife and bootstrap randomization methods. Male and female longevity was substantially reduced at the higher temperatures in contrast to intermediate and lower temperatures. According to a second order polynomial regression function, high correlations were observed between temperatures and the age of first reproduction as well as temperature and oviposition times. Net reproductive rate was highest at 25 degrees C and 74.172, while the intrinsic rate of increase displayed its highest values at 30 degrees C and was estimated to be 0.238. Birth rate and finite capacity of increase were higher at 30 degrees C and estimated to be 0.235 and 1.268, respectively. Mean generation time and doubling time varied significantly with temperature and the shortest mean generation and doubling time was obtained at 30 degrees C (25.566 and 2.909 d respectively). Life expectancy had its lowest value 10.3 d at 25 degrees C, whereas cohorts that were maintained at 20 and 15 degrees C increased their life expectation approximately three to sixfold.

An insect trypsin-like serine protease as a target of microRNA: utilization of microRNA mimics and inhibitors by oral feeding

MicroRNAs (miRNAs) are non-coding small RNAs (18-25 nt) that play crucial roles in various biological processes, including development, as gene regulators. In this study, we identified a miRNA, har-miR-2002b, that is specifically expressed during larval stages of Helicoverpa armigera (cotton bollworm). For the first time, we explored the possibility of utilizing synthetic inhibitor and mimic of a miRNA by oral feeding and confirmed that the inhibitor and mimic can successfully inhibit/oversupply har-miR-2002b in H. armigera larvae. Bioassays by oral feeding indicated 70% reduction in fecundity and 40% larval mortality in the presence of har-miR-2002b mimic. In addition, a large proportion of those larvae that made it to the pupal stage were deformed and only few moths emerged from them. This implied an important role of har-miR-2002b in larval development and adult fecundity. A trypsin-like serine protease (Ha-TLP) was identified as a target of har-miR-2002b. In vivo and in vitro studies revealed that in the presence of the miRNA mimic Ha-TLP transcript/protein levels and enzyme activity were significantly reduced. In contrast, inhibition of har-miR-2002b led to significant up-regulation of Ha-TLP transcript levels. This is the first study which shows the potential of utilization of miRNA mimics and inhibitors in pest control by targeting specific insect genes.

Nutritional indices and midgut enzymatic activity of Phthorimaea operculella (Lepidoptera: Gelechiidae) larvae fed different potato germplasms

The effect of 10 potato cultivars and clones on the feeding and digestion of Phthorimaea operculella (Zeller) larvae was evaluated using larval nutritional indices and enzymatic activities. Studies were based on nutritional indices from larvae reared at 25 +/- 1 degrees C, 65 +/- 5% relative humidity, and in complete darkness. The results of nutritional indices showed that conversion efficiency of ingested and digested food in the larvae at the fourth instar was the highest in Savalan cultivar at rates of 22.30 +/- 0.39 and 32.87 +/- 0.69%, respectively, and the lowest were recorded on Morene at rates of 15.83 +/- 0.35 and 21.99 +/- 0.58%, respectively. Among the different potato germplasms tested in the study, the highest proteolytic and amylolytic activities of the larvae, at optimal pH were in Morene with records of 8.204 +/- 0.296 U/mg and 0.071 +/- 0.0004 mU/mg, respectively; and the lowest were recorded in larvae fed on Savalan at 2.740 +/- 0.131 U/mg and 0.028 +/- 0.0001 mU/mg, respectively. It is concluded that Morene was the most unsuitable host for P. operculella.

Purification of a Kunitz-type inhibitor from Acacia polyphyllaDC seeds: characterization and insecticidal properties against Anagasta kuehniella Zeller (Lepidoptera: Pyralidae)

Anagasta kuehniella is a polyphagous pest that causes economic losses worldwide. This species produces serine proteases as its major enzymes for protein digestion. In this study, a new serine-protease inhibitor was isolated from Acacia polyphylla seeds (AcKI).Further analysis revealed that AcKI is formed by two polypeptide chains with a relative molecular mass of ∼20 kDa. The effects of AcKI on the development, survival, and enzymatic activity of Anagasta kuehniella larvae were evaluated, by incorporating AcKI in an artificial diet. Bioassays revealed a reduction in larval weight of ∼50% with the lower concentration of AcKI used in the study (0.5%). Although additionalassays showed an increase in endogenous trypsin and chymotrypsin activities, with a degree of AcKI-insensivity, AcKI produces an anti nutritional effect on A. kuehniella, indicating AcKI as a promising bioinsecticide protein for engineering plants that are resistant to insect pests.

Two Minus-C odorant binding proteins from Helicoverpa armigera display higher ligand binding affinity at acidic pH than neutral pH

Odorant-binding proteins (OBPs), widely and abundantly expressed in insect olfactory organs, are important for insect olfaction. In this study, two novel Minus-C OBP genes (HarmOBP17 and HarmOBP18) were characterized from the cotton bollworm, Helicoverpa armigera, one of the most important pests in cotton and other crops. Quantitative RT-PCR results indicate that the expression levels of the two genes differed greatly in regard to developmental stages, tissues, and genders. Binding properties of the two OBPs with plant volatiles were investigated at different pH levels using a competitive binding assay. Both OBPs displayed the highest binding affinities (Ki<13 μM) with Beta-ionone among the 85 tested compounds. Surprisingly, the two OBPs (HarmOBP17 in particular) displayed higher binding at pH 5.0 than at pH 7.4 and 10.0. This is the first reported Lepidopteran OBPs showing a contrary pH-dependent ligand binding behavior to other OBPs, implying a different mechanism of ligand binding and release. In addition, binding assays of the mutant OBPs (with the C-terminus eliminated) showed that the C-terminus was important for the ligand binding, but this importance varied with different ligands and OBPs, suggesting that their binding properties depend on the specific interactions between OBP and ligand.

Effects of lindane on lindane-degrading Azotobacter chroococcum; evaluation of toxicity of possible degradation product(s) on plant and insect

The effects of lindane on growth and plant growth-promoting traits of two lindane-degrading Azotobacter chroococcum strains (JL 15 and JL 104) were determined. The potential of both A. chroococcum strains to degrade lindane was also determined. Lower concentrations of lindane had a stimulatory effect, and higher concentrations generally had an inhibitory effect on growth and plant growth-promoting activities. A high percentage (>90%) of lindane was degraded by both strains at a lindane concentration of 10 ppm. Lindane at 1,000 ppm decreased seed germination and reduced seedling fresh weight. However, the possible degradation products for a starting lindane concentration of 10 ppm was found to be non-phytotoxic. Toxicity studies with larvae of Spilarctia obliqua resulted in an LC50 estimate of 3.41 ppm for lindane solutions into which leaf discs were dipped. No toxicity was observed for possible degradation products.

Different pattern of Galleria mellonella jhbp gene expression in high five and Sf9 cells

Juvenile hormone binding protein (JHBP) is the key element of the system that transmits hormone signals to target tissues. Recently, we found that the core promoter of the jhbp gene is strongly under the control of the TATA box and the transcription start site. In this report, we have shown that the jhbp promoter contains distal regulatory elements whose functionality clearly depends on the particular cell environment and that the scope of research from one cell line is insufficient to generalize the conclusions of the analysis. Cf1/Usp (where Usp is ultraspiracle protein previously known as Cf1, chorion factor 1) elements suppressed transcription of the reporter gene in the High Five cell line but not in the Sf9 cell line. However, upstream from all three Cf1/Usp elements there is a DNA sequence, containing the Zeste element, which activates jhbp in both systems. We found that juvenile hormone strongly inhibited the activity of the jhbp promoter in the Sf9 cell line, whereas it did not have an effect in the High Five cell line. A second key hormone that controls insect development--20-hydroxyecdysone, was also found to suppress the transcription of jhbp. This is the first report describing how these two hormones affect jhbp gene expression in different cell lines.

A regulatory pathway, ecdysone-transcription factor relish-cathepsin L, is involved in insect fat body dissociation

Insect fat body is the organ for intermediary metabolism, comparable to vertebrate liver and adipose tissue. Larval fat body is disintegrated to individual fat body cells and then adult fat body is remodeled at the pupal stage. However, little is known about the dissociation mechanism. We find that the moth Helicoverpa armigera cathepsin L (Har-CL) is expressed heavily in the fat body and is released from fat body cells into the extracellular matrix. The inhibitor and RNAi experiments demonstrate that Har-CL functions in the fat body dissociation in H. armigera. Further, a nuclear protein is identified to be transcription factor Har-Relish, which was found in insect immune response and specifically binds to the promoter of Har-CL gene to regulate its activity. Har-Relish also responds to the steroid hormone ecdysone. Thus, the dissociation of the larval fat body is involved in the hormone (ecdysone)-transcription factor (Relish)-target gene (cathepsin L) regulatory pathway.

Insect fat body is the intermediary metabolism organ and the main source of hemolymph components, and it is crucial for insect development and metamorphosis. However, molecular mechanism for the fat body remodeling is almost unknown other than in Drosophila melanogaster. A pupal diapause species the cotton bollworm, Helicoverpa armigera (Har), is a useful model to study individual or tissue remodeling, because larval fat body will remain integral in diapause-type pupae for months, whereas the dissociation of larval fat body will start on day 0 after pupation in nondiapause-type ones. Here, we find that H. armigera cathepsin L (Har-CL) is released from fat body cells into the extracellular matrix for tissue dissociation. A nuclear protein is identified to be transcription factor Har-Relish, which regulates the promoter activity of Har-CL gene. Har-Relish also responds to the steroid hormone ecdysone. Thus, a new regulatory mechanism, ecdysone-Relish-cathepsin L signaling pathway, is involved in the larval fat body dissociation.