An iridescent virus of the bollworm Heliothis zea (Lepidoptera:Noctuidae)

Larvae of Heliothis zea exhibiting iridescent lavender-blue, blue, blue-green color were obtained in spring field collections in host plants on a road right-of-way in Bolivar County, Mississippi. An iridescent virus was isolated and purified from these larvae. Size range of the virus was 131 to 160 nm, with a mean ± SD of 145 ± 6.5. The nucleic acid content was: DNA, 13.97 ± 1.58% (0.139 μg of DNA/mg of viral protein); RNA, none. Experimental infection was not achieved per os, but the virus was highly virulent by intrahemocoelic injection. The virus from larvae killed in this way was of the same size and morphology as that obtained in the initial isolation.     

A newly isolated densonucleosis virus from Pseudoplusia includens (Lepidoptera: Noctuidae)

An icosahedral DNA virus isolated from the soybean looper, Pseudoplusia includens, was characterized. Purified virus had a diameter of 20 ± 1 nm and negatively stained preparations showed a trend to form linear to three-dimensional crystals. The virus had a sedimentation coefficient of 120 ± 3 S and a buoyant density of 1.40 ± 0.01 g/cm³. The DNA content of the virus was 37.8 ± 0.1% and the absorption spectrum showed it to be a typical nucleoprotein. Viral DNA in situ was shown to be single-stranded by staining the virus with acridine orange as well as by reaction to formaldehyde. Evidence of inverted terminal repetition of the DNA was observed by electron microscopy. The terminal repetition comprises ca. 6–7% of the genome. The molecular weight of the ssDNA was 2.0 ± 0.1 × 10⁶ as determined by agarose gel electrophoresis or 2.1 ± 0.1 × 10⁶ as determined by electron microscopy. Four virion proteins with molecular weights of 46.5 ± 0.1, 54.0 ± 0.1, 64.0 ± 0.2, and 87.0 ± 0.1 × 10³ were detected by 9% SDS-polyacrylamide gel electrophoresis. Double-diffusion tests showed the virus to be serologically related but not identical to DNV-1. Ultrathin sections showed that the nucleus of the hemocyte, muscle, hypodermal, and fat body cells contained virus-like particles. The chromatin of an infected nucleus always underwent a margination and the nucleoplasm was often replaced largely by virions.Data indicate that the virus belongs to the Densovirus of the family Parvoviridae.     

Heliothis zea larval mortality time from topical and per os dosages of Nomuraea rileyi conidia

Heliothis zea larval mortality time was established for topical applications and per os (feeding) with fungal conidia of Nomuraea rileyi. The 6-to 7-day-old larvae received per os dosages ranging from 6 × 10⁶ to 9 × 10⁹ and a topical dosage of ca. 1 × 10⁹. These spore loads initiated fungal infections in larvae resulting in 1.5–100% accumulated mortality during the 30-day testing periods. The data indicated that regardless of the larval treatment method (topical or per os), or conidial dosage rates, the larval mortality time was never shorter than 5 days post-treatment, nor longer than 22 days. The highest percentage of larval deaths occurred from 7 to 9 days with a maximum mortality at 8 days.     

Trans-ovum transmission of a cytoplasmic polyhedrosis virus of Heliothis virescens (Lepidoptera: Noctuidae)

Adults of Heliothis virescens infected with a cytoplasmic polyhedrosis virus (CPV) produced healthy offspring when their eggs were surface sterilized with either 15% formaldehyde or 0.2% sodium hypochlorite solution. Larvae from infected parents (1) cultured on a vitamin-deficient medium, (2) exposed to cold treatment (5°C, 24 hr), or (3) as progeny of adults from diapaused infected pupae, produced the same number of infected individuals as larvae reared in the customary way. Field studies indicated that the percent of CPV infection in larvae originating from virus-infected parents was density dependent.     

Dissolution of Autographa californica nuclear polyhedrosis virus polyhedra by the digestive fluid of Trichoplusia ni (Lepidoptera:Noctuidae) larvae

The dissolution of polyhedra of Autographa californica nuclear polyhedrosis virus by digestive fluid collected from 5th stage Trichoplusia ni larvae was studied in vitro. Observations were made at timed intervals using phase contrast microscopy, and scanning and transmission electron microscopy. Dissolution occurred rapidly and in a detectable sequence. Under phase contrast, most polyhedra lost their refringence by 0.5 min. The polyhedra became rounded in appearance with small protuberances on the surface and Brownian movement was observed within. After 1 min, the envelope of most polyhedra had ruptured, releasing the enclosed virions. The protuberances were also observed under the scanning electron microscope after digestion for 0.5 min. Many shell fragments devoid of internal contents were seen after more lengthy digestion. Internal structural changes were revealed by electron microscopy. After 1 min of exposure, polyhedra were observed in all stages of dissolution. By 3 min, only virions, scattered about in heterogeneous material, could be distinguished.     

Lipophilic polypeptides of Chilo iridescent virus (CIV, type 6) membrane

Abstract In order to characterize associations between lipids and polypeptides of the Chilo Iridescent Virus (CIV) unit membrane, lipophilic polypeptides were selectively extracted from purified particles and analyzed. Polypeptides of MW 11 000, 12 500, 16 000, 18 000 and 50 000 were identified by electrophoresis: P11 000 seems to be linked with a fatty acid (palmitic acid), P12 500 is a DNA-binding protein and remains as a contaminant in lipophilic compounds, P16 000, P18 000 and P50 000 are strongly associated with phospholipids as phophatidylinositol (PI) in majority and phosphatidylcholine (PC). This result is of particular interest to explain the high proportion of PI in lipid analysis of the viral membrane.     

Thoracic mechanoreceptors in the wing bases of Heliothis zea (Lepidoptera: Noctuidae) and their central projections

The thoracic mechanoreceptors of the wings and their central projections in the noctuid moth Heliothis zea (Lepidoptera: Noctuidae) were investigated using cobalt chloride infiltration methods. The different mechanoreceptors, tegula, campaniform sensilla, and chordotonal organ were identified as being present in the wing bases. The forewing and hindwing bases were innervated by two large nerve trunks (IIN1 and IIIN1, respectively). Terminal projections for both wing bases included massive regions within the fused meso-metathoracic and prothoracic ganglia, as well as direct projections to the suboesophageal ganglia. The terminal fields of IIIN1 were exclusively ipsilateral, whereas those of IIN1 also were contralateral. The relationship of these sensory mechanoreceptors to the neural basis of evasive flight behaviours is discussed.     

Infectivity of an iridescent virus for larvae of Anticarsia gemmatalis (Lepidoptera: Noctuidae)

Laboratory tests were conducted with an iridescent virus (IV) of Anticarsia gemmatalis from Argentina to determine its infectivity for all six larval instars. For first, second, and third instars, the LC₅₀ values were 5.93, 6.14, and 11.30 mg/ml, respectively. The LD₅₀ values for fourth, fifth, and sixth instars were 1.21, 3.12, and 1.31μg/mg, respectively. The time until death was greater for early instars than for late instars; first instars averaged 23.1 days, second instars 19.6 days, third instars 19.5 days, fourth instars 14.3 days, fifth instars 8.2 days and sixth instars 6.5 days until death. High levels of iridescent virus inoculum appeared to activate a latent nuclear polyhedrosis virus in an average of less than 10% of larvae succumbing to a viral infection. Variable mortality rates were caused with low levels of IV inoculum; high dosages produced a high percentage of mortality, but it was virtually impossible to raise levels of inoculum to concentrations sufficient to produce 100% mortality.     

Susceptibilities of Helicoverpa zea and Heliothis virescens (Lepidoptera: Noctuidae) populations to Cry1Ac insecticidal protein

Susceptibilities of bollworm, Helicoverpa zea (Boddie) and tobacco budworm, Heliothis virescens (F.) to Cry1Ac were measured via a diet-incorporated assay with MPV II at the University of Arkansas during 2002-2004. Lethal concentration-mortality (LC50) estimates of five laboratory, seven laboratory-cross, and 10 field populations of H. virescens varied 12-fold. Pooled susceptibilities of H. virescens across all laboratory and field populations varied five-fold. The LC50 estimates for H. virescens were higher than those reported by previous research before the introduction of transgenic crops. However, the ratio of susceptibility of laboratory and field populations was similar, suggesting no change in overall species susceptibility. Individual LC50 estimates of five laboratory, nine laboratory-cross, and 57 field populations of H. zea varied over 130-fold. Pooled susceptibilities across laboratory and field populations varied widely. Among the field populations, colonies from non-Bacillus thuringiensis (Bt) crops were generally more susceptible than those from Bt crops. Across the Bt crops expressing Cry protein, colonies from Bollgard (Monsanto Company) cotton had lower susceptibility to CrylAc than those from Bt corn and those from non-Bt crops.     

Cold hardiness of Helicoverpa zea (Lepidoptera: Noctuidae) pupae

An insect's cold hardiness affects its potential to overwinter and outbreak in different geographic regions. In this study, we characterized the response of Helicoverpa zea (Boddie) pupae to low temperatures by using controlled laboratory measurements of supercooling point (SCP), lower lethal temperature (LT(50)), and lower lethal time (LLTime). The impact of diapause, acclimation, and sex on the cold hardiness of the pupae also were evaluated. Sex did not significantly affect the SCP, LT(50), or LLTime. However, the mean SCP of diapausing pupae (-19.3°C) was significantly lower than nondiapausing pupae (-16.4°C). Acclimation of nondiapausing pupae to constant temperatures from 10 to 20°C before supercooling also produced a significantly lower SCP than nondiapausing pupae held at 25°C. The LT(50)s of nondiapausing and diapausing were not significantly different, but confirmed that H. zea pupae are chill-intolerant because these lethal temperatures are warmer than the corresponding mean SCPs. Diapausing pupae survived longer than nondiapausing pupae at the same, constant, cold temperatures, a finding consistent with the SCP results. Both of these results suggest enhanced cold hardiness in diapausing pupae. When laboratory results were compared with field temperatures and observed distributions of H. zea in the contiguous United States, the laboratory results corroborated what is currently perceived to be the northern overwintering limit of H. zea; approximately the 40(th) parallel. Moreover, our research showed that areas north of this limit are lethal to overwintering pupae not because of low temperature extremes, but rather the length of time spent at near-zero temperatures.     

The biology of Chilo iridescent virus

Chilo iridescent virus (CIV) is the type species for genus Iridovirus, and belongs to the family Iridoviridae. Since the discovery of CIV in 1966, many attempts were made to elucidate the viral genome structure. The virions contain a single linear ds DNA molecule that is circularly permuted and terminally redundant. The genome of CIV has been entirely sequenced. The CIV virion consists of an unusual three-layer structure containing an outer proteinaceous capsid, an intermediate lipid membrane, and a core DNA-protein complex containing the genome. CIV has a broad host spectrum and has, in general, a limited mortality effect on its hosts. Up to now there have been several studies about CIV describing its structure, ecology, and molecular biology. In this review study we present all these studies together to describe the CIV.     

Long-term seasonal abundance patterns of Helicoverpa zea and Heliothis virescens (Lepidoptera: Noctuidae) in the Texas High Plains

Bollworm, Helicoverpa zea (Boddie), and tobacco budworm, Heliothis virescens (F.), male adult (moth) activities were monitored between 1982 and 1995 by using sex pheromone traps in the Texas High Plains. Moths were monitored weekly from early March to mid-November near Lubbock and Halfway, two prominent cotton production areas in the Texas High Plains region. Based on trap captures, the bollworm-budworm complex consisted of approximately 98% bollworms and approximately 2% tobacco budworms. Seasonal activity patterns varied between location for bollworm but not for tobacco budworm. The 14-yr average (+/- SE) bollworm moth abundance (moths per trap per week) at Lubbock was significantly higher (226.5 +/- 10.4) compared with that at Halfway (153.7 +/- 8.1). Correlation analyses showed a significant positive relationship between moth abundance and average weekly temperatures, whereas a significant negative relationship was observed between moth abundance and average weekly wind velocity for both species. Analyses also showed a positive correlation between moth abundance and cumulative degree-days (> 0.0 degrees C) from 1 January. A strong positive relationship was observed between moth abundance and weekly average precipitation for both species. Average weekly abundances were positively correlated between adjacent months during most of the active cotton fruiting season (June-September). However, the relationship between populations that contributed to the overwintering generation and the following spring populations varied between species and study sites. Nevertheless, data from this study indicated that late-season moth catches could be indicative of the dynamics of the early-season moth catches the following year in the High Plains. The mean population abundance curve based on 14-yr averages showed two bollworm population peaks at Lubbock, but only one peak at Halfway. Separate degree-day-based models were developed to describe long-term seasonal abundance patterns of bollworm moths for the Lubbock and Halfway sites.     

Overwintering of Heliothis virescens (F.) and Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) in cotton fields of northeast Mississippi

Following the 1995-2001 crop seasons, population densities of pupae of tobacco budworm, Heliothis virescens (F.), and corn earworm, Helicoverpa zea (Boddie), overwintering in cotton fields, Gossypium hirsutum L., in Monroe County, MS, were estimated by digging a total of 43,542 m-row. Densities of pupae varied greatly among years with the highest densities occurring in years with low rainfall in the late summer and early fall. The sex ratio of pupae was variable and significantly male-biased in some years. The total area-wide, tobacco budworm population emerging from all overwintering sites was estimated from catches in pheromone traps whose absolute efficiency is known. After the introduction of Bacillus thuringiensis Berliner (Bt)-transgenic cotton in 1996 but before a several-fold increase in use of herbicide resistant (HR)-transgenic cotton cultivars in 2001, local cotton fields accounted for <2% of the total overwintered tobacco budworm population. In the pretransgenic cotton production era, it is estimated cotton fields typically accounted for <10% of the overwintered tobacco budworm population. Driving surveys of the tillage status of cotton fields and pheromone trapping to determine the timing of adult emergence in the spring indicate that--until the 2000 crop season--postseason tillage destroyed most tobacco budworm and corn earworm pupae overwintering in cotton fields. Adoption of HR-transgenic cultivars has quintupled cotton field area planted no-till, but the contribution of cotton fields to overwintered tobacco budworm populations has remained low. Preemptive tillage of cotton fields to kill overwintering tobacco budworm pupae would not appreciably suppress in-season population densities of this pest. However, the absence of such tillage might increase the rate at which the tobacco budworm develops resistance to insecticides and counteradaptation to antibiotic host plant resistance traits including the Bt-transgenic trait.     

自同安钮夜蛾幼虫分离的一种核型多角体病毒

对在林间导致同安钮夜蛾Anua indiscriminate Moore幼虫死亡的一种病原物进行了分离和鉴定,并对该病原物进行了室内毒力测定。结果表明：该病原物为核型多角体病毒, 定名为同安钮夜蛾核型多角体病毒(AiNPV)。其对同安钮夜蛾幼虫的致死浓度LC₅₀和LC₉₀分别为3.4×10⁴和3.8×10⁷ PIB/mL。     

Transmission of a nuclear polyhedrosis virus inHeliothis zea [Lep.: Noctuidae] larval populations on soybean

Transmission of a nuclear polyhedrosis virus (NPV) inHeliothis zea (Boddie) on soybean was examinated. Artificial infestations ofH. zea were established at densities of 6.5, 19.5 and 58.5 larvae/row-m. Additional larvae infected to die from NPV in the 2nd stage were released into subplots to simulate 5 and 25% mortality levels. Virus transmission from infected to noninfected larvae was correlated with the initial incidence of infection in the population but not the density of larvae/row-m. Deposition of virus on plants from cadavers of larvae that died of virus infection was correlated with the initial incidence of infection in the populations and the density of larvae/row-m. After pupation of larvae in the 1st population, noninfected larvae only were again released to examine transmission of viral inoculum remaining on plants and soil. The percent mortality of larvae collected from the 2nd release was low and did not differ significantly between treatments. The concentration of virus on foliage and in soil after the 2nd release was directly correlated with density of larvae/row-m but not the incidence of infection within the population in the 1st release. This material is based upon work supported in part by the U.S. Department of Agriculture under Agreement N^o 82 CRSR-2-1000.