Zea Populations Research Articles

Evaluation of Early-Season Baculovirus Treatment for Suppression of Heliothis virescens and Helicoverpa Zea (Lepidoptera: Noctuidae) Over a Wide Area

Pheromone trap counts of F1 male cotton bollworm, Helicoverpa zea (Boddie), and tobacco budworm, Heliothis virescens (F.), were used to assess the effect of areawide suppression achieved by early-season application of a Helicoverpa/Heliothis specific nuclear polyhedrosis virus. Eggs (F2) were collected from cotton and other hosts to characterize the surviving reproductive populations. Trap and egg collection sites were established at 1.6-km intervals (n = 5) in four cardinal directions from the center of control and treated plots (259 km2, ≍ 10 by 10 mil. Traps also were placed at five additional intervals in four cardinal directions beyond the treated plot to assess the effect of dispersal. The effect of treatment was demonstrated by deviations in trap capture patterns within a year between treated and control plots and between years in the treated plot. Rates of increase between generations were calculated from the number of moths captured in one generation divided by the number from the previous generation. The rate of increase for the first field generation of H. virescens in the treated plot (1990) was 13% compared with 38% in the control plot (1990) and 38% in the treated plot in the year before treahllent (1989). The rate of increase for the first field generation of H. zea was 36% in the treated plot (1990) compared with 55% in the control plot (1990) and 95% in the treated plot the year before treatment (1989). Rates of increase for both species in the subsequent generation remained low in the treated plot (1990) compared with the control plot (1990) and with the previous year (1989). Our results indicate that a single virus application can reduce the adult H. virescens and H. zea populations emerging from alternative hosts present early in the season. Other methods for improving the efficacy of treatments are discussed.

Soybean Yield Interaction between Helicoverpa zea Infestation and Simulated Frost Injury

AbstractSoybean, Glycine max (L.) Merr., yields may be reduced by corn earworm, Helicoverpa zea (Boddie), feeding and by early frosts. One consequence of H. zea feeding can be a delay in pod development. A consequence of frost injury can be shortening of the seed fill duration. The objective of 12 experiments conducted at multiple locations from 1984 to 1987 was to evaluate the potential for an interaction between H. zea feeding damage and early frost. Insecticides were used to establish varying levels of H. zea populations in soybean and paraquat (1,1′.dimethyl‐4,4′‐bipyridinium dichloride) was used to simulate frost injury. Significant yield differences between levels of H. zea populations were detected in eight experiments, and paraquat treatments significantly reduced yields in 11 experiments. A significant interaction between H. zea population level and paraquat treatment time occurred in three experiments. In these experiments, yield reduction due to paraquat was greater where H. zea populations were larger. Although soybean can compensate for a delay in pod set caused by H. zea feeding in most years, when seed fill period is shortened, as would occur with early frost, a delay in pod set can contribute to yield loss. Identifying one of the many factors that lead to variation in yield loss from a particular level of H. zea infestation, is a step towards more effective management of this pest.

Helicoverpa zea (Lepidoptera: Noctuidae) Pupa Production in Fruiting Com in Northeast Mexico and South Texas

Populations of corn earworm, Helicoverpa zea (Boddie), pupae produced in ≍200,000 ha of corn growing in the Lower Rio Grande Valley of northeast Tamaulipas Mexico and south Texas were estimated. Pupae were excavated from two soil samples (1m2) in 90–120 cornfields each year between 1985 and 1988 following larval development on ear-stage corn. Mean plant populations in the fields ranged from 5.6 per meter of row in 1987 to 6.8 per meter of row in 1986, while ear infestation by H. zea larvae ranged from 76.9% in 1987 to 93.6% in 1986. The total number of corn earworm prepupae, pupae, and exuviae excavated ranged from an average 1.1 insects per square meter in 1987 to 3.8 insects per square meter in 1985. Correlation analysis indicated that only 58% of the variation in the number of corn earworm excavated from the 1-m2 soil samples was correlated with the variation in the number of infested plants per meter of row. Estimates of the number of live pupae produced from 200,000 ha of ear-stage corn in the Lower Rio Grande Valley ranged from 1.48 × 109 in 1987 to 7.16 × 109 in 1985. The potential for adult H. zea populations emerging from ear-stage corn to affect other crops subsequently is discussed.

Preventing insect adaptation to insect-resistant crops: are seed mixtures or refugia the best strategy?

Transgenic crops expressing insecticidal toxins could soon provide safe, clean and effective means of pest control, but their usefulness will be short-lived if insects adapt to the toxins. Two planting strategies are among those that have been recommended to delay crop failure: susceptible insects could be conserved by planting either ‘refugia’, i.e. separate fields of toxic and toxin-free crop, or ‘seed mixtures’ of toxic and toxin-free plants in the same fields. However, we show that if insects can move from plant to plant, seed mixtures may actually hasten insect resistance compared with pure stands of toxic plants. Insect movement causes an increase in effective genetic dominance which can counteract reduced selection due to the mixture. This failure of seed mixtures is likely under just those conditions, low genetic dominance of resistance, which predict a good chance for resistance to the toxin to evolve slowly. Seed mixtures, unlike refugia, are therefore failure prone. This result also suggests potential problems with a third strategy, tissue-specific expression of toxins, which essentially provides a mixture of toxin-free and toxin-containing tissues on the same plant. However, better information and modelling are urgently required to evaluate alternative means of slowing insect adaptation to resistant crop plants. Legislation for toxinfree refugia may provide one of the best available means for conserving insect susceptibility.

Effects of Inherited Sterility and Insect Resistant Dent-Corn Silks on Helicoverpa zea (Lepidoptera: Noctuidae) Development

Male and female corn earworm, Helicoverpa zea (Boddie), adults were exposed to a substerilizing dose (10 krads) of gamma radiation after which their progeny were reared on a meridic diet containing selected concentrations of dry silk collected from resistant dent corn genotypes. Significant interactions were observed between the developmental time of progeny from irradiated females and progeny from normal parents and meridic diets with increasing degrees of resistance. A significant interaction also was observed between the mean larval weights of normal and substerile larvae and diets with increasing degrees of resistance. The 9-d weight of normal larvae was significantly higher than the weight of substerile larvae at the lowest degree of resistance, but differences between the weight of normal and substerile larvae at the highest degree of resistance were not significant. Larvae from irradiated male by normal female crosses were equally competitive with normal larvae for all measured parameters. Data from this study suggest that plant resistance and inherited sterility would be compatible control strategies for the management of H. zea populations.

Reductions in Soybean Yield and Quality from Corn Earworm Flower Feeding

AbstractSoybean, Glycine max (L.) Merr., defoliation and pod feeding by corn earworm, Helicoverpa zea (Boddie), are often considered types of injury that lead to yield and quality reductions. When infestations coincide with the flowering period, however, density of H. zea larvae is higher on flowers than on other plant parts. Experiments were conducted to assess yield reductions relative to H. zea feeding on flowers, foliage, and pods. Populations of H. zea were manipulated with insecticides at two locations in 1983 and 1984 to achieve varying densities in soybean. Flower numbers, leaf area, and pod numbers were reduced in treatments with larger populations of corn earworm larvae. In addition, fewer flowers were shed from plants with large H. zea populations, and in one trial, pod shed was also decreased. Flower removal by H. zea larvae resulted in a delay in pod set. At harvest, the number of seeds per pod was reduced in three trials that had the largest H. zea populations. Seed weight was increased or decreased by H. zea injury. Injury by H. zea sometimes increased percent soybean seed protein and sometimes reduced harvestable yield. Flower feeding contributed to yield losses by delaying pod set.

Response of Helicoverpa zea (Lepidoptera: Noctuidae) Populations to Canopy Development in Soybean as Influenced by Heterodera glycines (Nematoda: Heteroderidae) and Annual Weed Population Densities

Field experiments to investigate the interactive effects among corn earworm, Helicoverpa zea (Boddie);soybean cyst nematode, Heterodera glycines Ichinohe; and annual weed species in soybean ( Glycine max (L.) Merrill) were conducted during 1986-1988 in eastern North Carolina, This study examined the effects of canopy development in soybean on H. zea oviposition and larval establishment as influenced by H. glycines and weed densities. Soybean canopy development was inversely related to increasing initial population density (PI) of H. glycines . In general, soybeans with moderate and high H. glycines P, levels had more open canopies and consequently had greater H. zea larval populations during mid- to late August than did the 0 and low H. glycines P, treatments where soybean canopies were closed, In some field sites, very high H. glycines P, levels caused severe stunting and chlorosis, reducing the suitability of these soybeans as a food source for H. zea larvae, Weed-free and moderately weedy soybeans had greater H. zea larval populations than soybeans with high weed densities. Across locations and years, numbers of early developmental stages (egg and early instars) of H. zea were not influenced by l H. glycines P1 or weed density. Numbers of H. zea late instars were positively correlated with distance between canopies of adjacent rows.

Parasitization of Lepidopterans as Affected by Nematicide-Insecticide Use in Soybean

Larvae of green cloverworm, Plathypena scabra (F.), soybean looper, Pseudoplusta Tncludens (Walker), and corn earworm, Heltothis zea (Boddie), were sampled in soybean plots (maturity groups V and VII) treated with high rates of aldicarb, carbofuran, and fenamiphos for nematode control and with acephate for thrips control. Larval collections from both maturity groups indicated that the most abundant parasitoid of lepidopterous larvae in soybean treated with nematicide and insecticide was Cotesia margintventris (Cresson), which was responsible for > 90% of the parasitism in 1984 and 1985. Thirty-three percent of small Plathypena scabra were parasitized in 1984; 23% were parasitized in 1985. None of the treatments appeared to affect the occurrence of parasitism in Plathypena scabra larvae adversely. Soybean treated with aldicarb hosted significantly more Plathypena scabra and parasitoids than untreated plots. Soybean (maturity group V) hosted significantly higher H. zea populations in soybean treated with carbofuran (1984) or aldicarb (1985) than in untreated control plots. Heliothis nuclear polyhedrosis virus and the parasitoids Microplttis croceipes (Cresson) and Cotesia marginiventris were important in regulating H. zea populations.

Interaction of nuclear polyhedrosis virus with catechols: Potential incompatibility for host-plant resistance against noctuid larvae

Two major orthodihydroxy phenolics ofLycopersicon esculentum, rutin and chlorogenic acid, have previously been identified as potential sources of host-plant resistance against the tomato fruitwormHeliothis zea. We report here the possible incompatibility of these chemically based resistance factors with viral control ofH, zea. We have found that both rutin and chlorogenic acid significantly inhibited the infectivity of nuclear polyhedrosis viruses. Chlorogenic acid, when added to tissue culture medium containing TN-368 ovarian cells, inhibited the infectivity of a multiply embedded virus (AcMNPV) by over 86%. Rutin or chlorogenic acid, when fed toH. zea, inhibited the infectivity of a singly embedded nuclear polyhedrosis virus (HzSNPV), with the greatest degree of inhibition occurring at low doses of viral inoculum. Additionally, the ingestion of these phytochemicals significantly prolonged the survival time of virally infectedH. zea larvae. These results suggest that the effectiveness of nuclear polyhedrosis viruses in controllingH. zea populations may be adversely affected by varieties ofL. esculentum with significant levels (eg. 3.5 μmol/g wet weight) of rutin or chlorogenic acid.

Ecological, Agricultural, Genetic, and Commercial Considerations in the Deployment of Insect-resistant Germplasm

We make an attempt to identify the agricultural and ecological factors of greatest importance in assessing the applicability of different modalities (antibiosis, antixenosis, tolerance) and levels of insect resistance to the pest management requirements of different crops and cropping systems. Emphasis is placed on the importance of matching the type and level of resistance to the pest's biology (e.g., feeding habits, development on the crop, alternate hosts, patterns of invasion of the crop, number of generations passed in the crop) and the production requirements of the crop. We illustrate how, depending on context, the use of a particular modality and level of resistance may simplify pest management, reduce crop losses without simplifying pest management, or by changing a pest whose occurrence in damaging populations is highly predictable to one whose occurrence is irregular and unpredictable, complicate pest management. The HELSIM Heliothis zea population dynamics model is used to illustrate how simulation models can be used to explore the consequences of deploying particular modalities and levels of insect resistance. In exploring genetic considerations in the use of insect-resistant germplasm, we focus on the problem of maximizing the durability of insect resistance by minimizing selection for virulent biotypes. We examine whether some modalities of resistance are inherently more stable than others regarding selection of virulent biotypes, and argue that in judging the inherent durability of a particular resistance, exclusive focus on the genetic nature of the plant resistance is inadequate. Knowledge of the genetic variability of the target pest vis a vis the plant resistance and an understanding of the direct biological effects of the resistance on the insect are also essential. The selection pressure for virulent insect biotypes exerted by resistant crop cultivars is shown to be dependent upon the modality of resistance as well as the agricultural and ecological context in which it is deployed. Simulation models are used to illustrate how different deployment strategies can affect the durability of resistance.

Baseline data for evaluating resistance development: Doseage/mortality studies using two test methods with chlorpyrifos, methomyl and permethrin inHeliothis virescens(F.) andHeliothis zea(Boddie) (Lepidoptera: Noctuidae)

Abstract Baseline data on the relative susceptibility of 17 Heliothis virescens (F.) and 20 Heliothis zea (Boddie) populations to commonly used Insecticides were determined. These data provide a benchmark for field populations, so that any future occurrence of resistance can be documented and quantified. Permethrin, methomyl and chlorpyrifos were tested over a 3 year period as representatives of pyrethroids, carbamates and organophosphates respectively. The various cultures showed high differences in susceptibility, and the level of variation generally agreed with earlier reports for these species. Using the topical application method there was a negative correlation between methomyl and chlorpyrifos sensitivity among the various strains. There was no correlation in rank between methomyl with permethrin or chlorpyrifos with permethrin. A second assay method, deposit‐on‐glass, was also used. In general, this test gave different results than topical application, and there was no correlation between the two ...

Corn Earworm Control on Soybean with CME 134, an Insect Growth Regulator, with Thuringiensin, a Beta-Exotoxin of Bacillus thuringiensis, and With Dipel 1985

Abstract Soybeans were planted in 40-inch rows at the Auburn University Plant Breeding Unit in east-central AL. Treatment plots (6 rows by 50 ft) were arranged in a randomized complete block design with 4 replicates. Treatments were applied on 6 Aug, when the number of H. zea larvae in the test field was ca. 1 per row ft. Applications were made with a CO2 pressurized backpack sprayer calibrated to deliver 13.68 gal/acre at 40 psi, through 3-TX4 hollow cone tip nozzles per row. All insect counts were made using the standard shake cloth technique. Two 6-ft samples were taken per plot, per sample date. A pretreatment sample was taken on 6 Aug. Posttreatment samples were taken on 9, 14, and 19 Aug, after which time the H. zea population declined in the test field.

Age‐specific survivorship analysis of Heliothis spp. Populations on cotton

SummaryPopulation dynamics of Heliothis virescens (F.) and Heliothis zea (Boddie) (Lepidoptera: Noctuidae) eggs and larvae were studied for two years in a small plot of cotton, Gossypium hirsutum (L.). Due to morphological and ecological similarities, the pooled Heliothis population was considered for most of the analyses. Two generations of Heliothis eggs and larvae were completed during each year. Stage recruitment was estimated for the eggs and larval instars 2–6, and recruitment variances were estimated by a Monte Carlo method. A modified form of the Weibull distribution was developed and used as a model to characterize survivorship curves for each of the four Heliothis generations. A Type I survivorship curve (mortality rate increasing with age) was inferred for both Generation 1 (early season) data sets, whereas a Type II survivorship curve (mortality rate constant and thus independent of age) was inferred for both Generation 2 (late season) data sets. The shapes of the survivorship curves for the individual H. virescens and H. zea populations were inferred to be the same as those for the pooled populations. Analysis of the contributions of various factors to Heliothis stage‐specific mortality indicated that natural enemies (predators and parasites) and the availability of food for larvae were responsible for between‐generation differences in survivorship patterns.

Heliothis spp. 1 Seasonal Incidence on Cotton in the Mississippi Delta 2

Data on adults reared in the laboratory from eggs and larvae collected from cotton fields indicated that changes in seasonal species composition in Heliothis occurred during the period from 1963 to 1979 in the delta of Mississippi. In the mid-60s, the population was predominantly H. zea (Boddie). In 1969, it changed to a predominantly H. virescens (F.) population and continued essentially as an H. virescens population through the 70s. In 1979, the population changed again to become a predominantly H. zea population. Adults reared from both eggs and larvae followed this pattern. The data also indicated that in most years a higher percentage of the adults reared from eggs than from larvae were H. virescens .

Effects of Vairimorpha necatrix in Sprays and Corn Meal on Heliothis Species in Tobacco, Soybeans, and Sorghum123

Vairimorpha necatrix (Kramer), a promising microbial control agent due to its virulence and prolificness in several lepidopterous pests, was evaluated as a microbial insecticide for the tobacco budworm, Heliothis virescens (F.), and corn earworm, H. zea (Boddie). Application in aqueous sprays at 2.5×1013 spores/ha did not adequately reduce density of budworm populations or damage in tobacco in spite of infection of up to 65% of the population. However, a V. necatrix-corn meal formulation, applied by hand above the tobacco vegetative bud at 2.5×1012 spores/ha, reduced budworm population density and damage to an extent comparable to a chemical insecticide or a Bacillus thuringiensis Berliner (Dipel®)-corn meal formulation. The hymenopterous parasites Campoletis sonorensis (Cameron) and Cardiochiles nigriceps Viereck were not infected by V. necatrix even when the parasites emerged from heavily infected budworms. Spray application of up to 3.2×1013 spores/ha did not adequately reduce H. zea populations or damage in soybeans or sorghum although infection of 99 and 72% of the host populations on the respective crops was attained. The microsporidium at the highest rate was, however, as effective as a chemical insecticide against the green cloverworm, Plathypena scabra (F.). The effectiveness of a Dipel- V. necatrix mixture was similar to that of Dipel alone against H. zea but less than Dipel alone against P. scabra.

Artificial Infestation of the Tomato with Eggs of the Tomato Fruitworm1

Field-grown tomatoes were artificially infested with Heliothis zea (Boddie) by applying a suspension of eggs in a 0.2% agar solution to the top surface of randomly located leaves. The degree of infestation depended largely upon the number of eggs applied. Fruit damage due to natural H. zea populations ranged from 6 to 10% and that due to the natural populations plus the maximal numbers of eggs tested, 3000–3200 eggs/plant, ranged from 51 to 54%. There was a curvilinear relationship between number of eggs and degree of fruit damage; damage increased as egg dosage increased but at a decreasing rate. Application of eggs was most effective ca. 1 mo before 1st harvest. Multiple or repeated applications were no more efficient than a single application of an equivalent number of eggs. Practical aspects of the choice of an appropriate damage rating criterion are discussed. The method seems satisfactory for use in screening tomatoes for resistance to H. zea .