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Interactions between the cotton bollworm,Helicoverpa armigera(Hübner) (Lepidoptera: Noctuidae), its larval parasitoidMicroplitis mediator(Haliday) (Hymenoptera: Braconidae), and the Cry1Ac toxin ofBacillus thuringiensisBerliner were evaluated under laboratory conditions. The growth ofH. armigeralarvae was delayed and its pupal rate and pupal weight decreased when they were fed on a diet containing Cry1Ac toxin. Due to the lowered growth rate of the host larvae, the time available for parasitization ofH. armigerabyM. mediatorincreased when the host larvae were reared on a diet containing Cry1Ac toxin at concentrations of 0.5, 1, 2, and 4 µg g−1. The longevity of female and male parasitoids was not significantly affected when newly emerging wasps fed on honey solutions containing three different concentrations of Cry1Ac toxin (125, 250, and 500 µg ml−1). When female parasitoids were fed on honey solutions containing Cry1Ac, their offsprings’ egg and larval development period, pupal weight, length of pupation, adult weight, and adult longevity did not change significantly in most of the treatments compared with controls. When the female parasitoids parasitized host larvae that had been fed on a diet containing 0.5, 1, 2, 4, and 8 µg g−1 Cry1Ac toxin, their offsprings’ eggs and larvae were significantly delayed. Their pupal weight, adult weight, and adult longevity were also significantly less than controls. [ABSTRACT FROM AUTHOR]

Abstract: Baculoviruses manipulate host climbing behaviour to ensure that the hosts die at elevated positions on host plants to facilitate virus proliferation and transmission, which is a process referred to as tree‐top disease. However, the detailed molecular mechanism underlying tree‐top disease has not been elucidated. Using transcriptome analysis, we showed that two hormone signals, juvenile hormone (JH) and 20‐hydroxyecdysone (20E), are key components involved in HaSNPV‐induced tree‐top disease in Helicoverpa armigera larvae. RNAi‐mediated knockdown and exogenous hormone treatment assays demonstrated that 20E inhibits virus‐induced tree‐top disease, while JH mediates tree‐top disease behaviour. Knockdown of BrZ2, a downstream signal of JH and 20E, promoted HaSNPV‐induced tree‐top disease. We also found that two miRNAs target BrZ2 and are involved in the cross‐talk regulation between 20E and JH manipulating HaSNPV replication, time to death and HaSNPV‐induced tree‐top disease. [ABSTRACT FROM AUTHOR]

Microplitis mediator (Hymenoptera: Braconidae) and Helicoverpa armigera nucleopolyhedrovirus (HearNPV) have been broadly used in field for management of cotton bollworm H. armigera (Lepidoptera: Noctuidae) and they both might share resource in the host larvae when simultaneously applied in the fields. This study explored the interactions between M. mediator and HearNPV in H. armigera through bioassay analysis. The mortality of H. armigera caused by HearNPV inoculation on 2 nd instars showed linear relationship with the concentration of the inoculated HearNPV, but the mortality due to HearNPV infection was reduced when HearNPV was inoculated on the third and fourth day post-parasitism by M. mediator . The mortality due to parasitism separately decreased with the increasing of the parasitism host instar. The performance of M. mediator , including survival rate, development duration and the cocoon weight declined with the reduction of interval between the parasitism and HearNPV inoculation. The analysis of co-toxicity factor demonstrated the antagonistic effect between M. mediator and HearNPV on H. armigera larvae when HearNPV was orally inoculated at 4 d post parasitism, however, additive effects were revealed when the intervals between virus infection and parasitism were 1, 2 or 3 days. These results indicated that the application of the HearNPV was unfriendly to the releasing of parasitoid M. mediator and the existence of M. mediator might weaken the virulence of baculovirus. The both HearNPV and M. mediator for management of H. armigera should not be used coincidently. [ABSTRACT FROM AUTHOR]

Apolygus lucorum (Meyer-Dür) (Hemiptera: Heteroptera: Miridae) is an important insect pest of cotton and other crops, but the species also feeds on some insect pests. In this study, the effect of 5 food condition treatments, including corn kernel, cotton leaves, eggs of Helicoverpa armigera Hübner (Lepidoptera: Noctuidae), a combination of corn + H. armigera eggs, and of cotton leaves + H. armigera eggs, on the biological parameters of A. lucorum was evaluated in the laboratory. Mixed foods (e.g., corn + H. armigera eggs) significantly increased nymphal survival, prolonged adult longevity, and improved female fecundity. The survival rate of nymphs with only H. armigera egg was the lowest, and development times with cotton leaves were the longest. Under mixed food conditions, nymphs preyed on more eggs in the combination with cotton leaves than with corn. These results indicate that A. lucorum does have a certain ability to prey on H. armigera eggs, but that during the growth and development of A. lucorum, plant food is still necessary for development. [ABSTRACT FROM AUTHOR]

Helicoverpa armigera single nucleocapsid nucleopolyhedrovirus (HearNPV) is an obligatory and lethal parasite of the cotton bollworm and has been extensively used in China for the control of this notorious pest. Digital gene expression (DGE) analysis was adopted for an overall comparison of transcriptome profiling between HearNPV-infected and control healthy Helicoverpa armigera larvae during an early stage post-inoculation. A total of 908 differentially expressed genes (DEGs) were identified, of which 136 were up-regulated and 597 were down-regulated. GO category and KEGG pathway analysis demonstrated that the identified DEGs involved in ribosome biogenesis, aminoacyl-tRNA biosynthesis, protein processing in endoplasmic reticulum, biosynthesis of valine, leucine, isoleucine and the spliceosome were significantly down-regulated, whereas genes involved in pancreatic secretion, protein digestion and absorption and salivary secretion showed obviously up-regulated transcription. The DEGs were verified by quantitative real-time PCR, and genes that participated in defensive response, nutritional digestion and developmental regulation exhibited specific expression patterns in a continuous time-course assessment. These results provide basic data for future research on the molecular mechanism of HearNPV infection and the interactions between lepidopteran hosts and their specific NPV parasites. [ABSTRACT FROM AUTHOR]

Thioredoxin peroxidases (Tpxs) play a crucial role in protection against oxidative damage in several insect species. However, studies on the characteristics and functions of Tpxs in Helicoverpa armigera are lacking. In this study, a novel 2-Cys Tpx gene from H. armigera ( HaTpx ) was identified. Sequence analysis revealed that HaTpx is highly conserved and shares two catalysis regions (VCP) with other insect species. HaTpx mRNA was found to be expressed in an age-dependent manner and was ubiquitous in all tissues examined. Hormone treatment showed that the expression of HaTpx is clearly induced by 20-hydroxyecdysone but repressed by Juvenile hormone. Additionally, extreme temperature, ultraviolet light, mechanical injury, Escherichia coli , Metarhizium anisopliae , nucleopolyhedrovirus (NPV) infection, and H 2 O 2 treatment markedly induced HaTpx gene expression. Reactive oxygen species (ROS) levels in hemocytes and MDA concentrations in the hemolymph after NPV infection were evaluated, and the results indicated that NPV infection causes excessive ROS generation. After knockdown of HaTpx by RNA interference, the expression of three antioxidant genes ( Cu / ZnSOD , Trx , and TrxR ) was increased, whereas two antioxidant genes (CAT and GPX) showed decreased expression. Moreover, the susceptibility of H. armigera to NPV infection increased after HaTpx knockdown. These results indicated that HaTpx contributes to the susceptibility of H. armigera to NPV, and the results also provide a theoretical basis for a novel strategy for developing new chemicals and microbial pesticides that target HaTpx gene for controlling H. armigera . [ABSTRACT FROM AUTHOR]

Visual genes may become inactive in species that inhabit poor light environments, and the function and regulation of opsin components in nocturnal moths are interesting topics. In this study, we cloned the ultraviolet (UV), blue (BL) and long-wavelength-sensitive (LW) opsin genes from the compound eye of the cotton bollworm and then measured their mRNA levels using quantitative real-time PCR. The mRNA levels fluctuated over a daily cycle, which might be an adaptation of a nocturnal lifestyle, and were dependent on a circadian clock. Cycling of opsin mRNA levels was disturbed by constant light or constant darkness, and the UV opsin gene was up-regulated after light exposure. Furthermore, the opsin genes tended to be down-regulated upon starvation. Thus, this study illustrates that opsin gene expression is determined by multiple endogenous and exogenous factors and is adapted to the need for nocturnal vision, suggesting that color vision may play an important role in the sensory ecology of nocturnal moths. [ABSTRACT FROM AUTHOR]

Abstract: In this study, interactions on the mortality and debilitating effects between Cry1Ac, a toxic protein produced by Bacillus thuringiensis (Berliner) and HaCPV (Chinese strain) on first and third instars larvae of Helicoverpa armigera were evaluated in laboratory. When first instar was exposed to combination of Bt cotton leaf discs containing HaCPV (6×106, 1×107, and 3×107 PIBml−1) the effect on mortality was additive, when such instar larvae exposed to combination of Cry1Ac (0.9, 2.7, or 8.1μgg−1) and the same concentrations of HaCPV the effect on mortality was additive except for the combination of Cry1Ac (0.3μgg−1) and HaCPV concentrations that showed synergism. When third instars of H. armigera were infected using a suspension containing both HaCPV and Cry1Ac, most combinations of them showed additive effect except for the combination of Cry1Ac (0.3μgg−1) and HaCPV (3×107 PIBml−1) that showed synergism. However, when they exposed to Bt cotton leaf discs and HaCPV the effect on mortality was synergism except combination of Bt cotton leaf discs and HaCPV (6×106 PIBml−1) that showed additive. Most of the combinations are showed additive effect in the toxicity and in combinations of Cry1Ac at lowest and HaCPV at highest concentrations synergism is observed. Not only were larval growth and development delayed, but pupation and pupal weight also decreased when larvae were fed on artificial diet containing Cry1Ac and HaCPV or transgenic Bt cotton leaf discs specially in first instar. [Copyright &y& Elsevier]

Abstract: Microplitis mediator (Haliday) is a solitary endoparasitoid of larvae of the cotton bollworm, Helicoverpa armigera (Hübner) and the oriental armyworm, Mythimna = Leucania separata (Walker). The preference and suitability of different instars of M. separata for M. mediator were determined under laboratory conditions at a constant temperature of 26±1°C, 65±5% RH and L14:D10 photoperiod. The selection coefficient revealed that M. mediator parasitized 1st to 4th instars, but preferred 2nd and 3rd instars. Seventy-one percent of parasitism was achieved within 24h when the 2nd instars were used as hosts at a density of one parasitoid per 20 Larvae. Parasitoid egression and pupation were dependent on the host instar parasitized and occurred from the 1st through the 4th instar. The mean developmental time from egg to prepupae of M. mediator within 1st to 4th instars of the host was 8.27, 8.30, 8.30 and 9.20 days, respectively. Cocoon weights were lower when 1st and 2nd instars served as hosts rather than 3rd and 4th instars. The percentage of host larva that died before parasitoid egression declined as the age of the host increased, ranging from 26% to 2% for 1st–5th instars, respectively. The results of this study suggest that 2nd and 3rd instars of M. separata would be the best host stages for mass production of M. mediator in the laboratory and the best host instars to target for effective control in field releases. [Copyright &y& Elsevier]

The thioredoxin system, including NADPH, thioredoxin (Trx), and thioredoxin reductase (TrxR), plays significant roles in maintaining intracellular redox homeostasis and protecting organisms against oxidative damage. In this study, the characteristics and functions of H. armigera HaTrx2 and HaTrxR1 were identified. Sequence analysis showed that HaTrx2 and HaTrxR1 were both highly conserved and shared high sequence identity with other insect counterparts. The mRNA of HaTrx2 was expressed the highest in 5th instar 96 h and was mainly detected in heads and epidermis. The expression of HaTrxR1 was highly concentrated in 5th instar 72 h and 96 h, and higher in malpighian tube, midgut and hemocyte than other examined tissues. HaTrx2 and HaTrxR1 were markedly induced by various types of stress. HaTrx2- or HaTrxR1-knockdown increased ROS production in hemocytes and also increased the lipid damage in NPV infected H. armigera larvae. Furthermore, interference with expression of HaTrx2 or HaTrxR1 transcripts in H. armigera larvae resulted in increased sensitivity to NPV infection and shortened LT50 values. Our findings indicated that HaTrx2 and HaTrxR1 contribute to the susceptibility of H. armigera to NPV and also provided the theoretical basis for the in-depth study of insect thioredoxin system. [ABSTRACT FROM AUTHOR]