Populations Of Tobacco Budworm Research Articles

Resistance monitoring of Heliothis virescens to pyramided cotton varieties with a hydrateable, artificial cotton leaf bioassay

Proof of concept was demonstrated for a practical, off-the-shelf bioassay to monitor for tobacco budworm resistance to pyramided Bt cotton using plant filtrates. The bioassay was based on a previously described feeding disruption test using hydrateable artificial diet containing a blue indicator dye, a diagnostic dose of insecticide and novel assay architecture. Using neonate larvae from a Bt-susceptible, laboratory reared tobacco budworm strain, a diagnostic dose for Bollgard II and WideStrike cotton was obtained that limited neonate blue fecal production to 0–2 pellets in 24 h (Bt-resistant larvae produced >2 fecal pellets). The bioassay was tested with three different field populations of tobacco budworm collected from tobacco in central North Carolina (USA) and shown to accurately diagnose susceptibility to Bt. The diagnostic doses were also successfully evaluated with two Bt-resistant, laboratory reared tobacco budworm strains. Shelf life studies showed the assay could be stored for at least 6 months at room temperature (longer storage times were not studied). The application of the bioassay as an easy to use monitoring tool is discussed.

Efficacy of Transgenic Cotton Expressing Cry1Ac and Cry1F Insecticidal Protein Against Heliothines (Lepidoptera: Noctuidae)

Cotton, Cossypium hirsutum L, plants expressing Cry1Ac and Cry1F (Phytogen 440W) insecticidal crystal proteins of Bacillus thuringiensis (Bt) Berliner, were evaluated against natural populations of tobacco budworm, Heliothis virescens (F.), and bollworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), across 13 southern U.S. locations that sustained low, moderate, and high infestations. The intrinsic activity of Phytogen 440W was compared with nontreated non-Bt cotton (PSC355) and with management strategies in which supplemental insecticides targeting heliothines were applied to Phytogen 440W and to PSC355 cotton. Infestations were composed primarily of bollworm, which is the least sensitive of the heliothine complex to Cry toxins. Therefore, damage recorded in these studies was primarily due to bollworm. Greater than 75% of all test sites sustained heliothine infestations categorized as moderate to high (10.6-64.0% peak damaged bolls in nontreated PSC355). Phytogen 440W, alone or managed with supplemental insecticide applications, reduced heliothine-damaged plant terminals, squares (flower buds), flowers, and bolls equal to or better (1.0-79.0-fold) than managing a non-Bt cotton variety with foliar insecticides across all infestation environments. Rarely (frequency of < or = 11% averaged across structures), sprayed Phytogen 440W reduced damaged structures compared with nontreated Phytogen 440W. Protection against heliothine-induced plant damage was similar across the three levels of infestation for each viable management strategy, with exception to damaged squares for nontreated Phytogen 440W. In situations of moderate to high heliothine infestations, cotton plants expressing Cry1Ac and Cry1F may sustain higher levels of damage compared with that same variety in low infestations. No significant difference in yield was observed among heliothine management strategies within each infestation level, indicating cotton plants may compensate for those levels of plant damage. These findings indicate Phytogen 440W containing Cry1Ac and Cry1F provided consistent control of heliothines across a range of environments and infestation levels.

Baseline Susceptibility of Tobacco Budworm (Lepidoptera: Noctuidae) to Cry1F Toxin from &lt;I&gt;Bacillus thuringiensis&lt;/I&gt;

Transgenic cotton, Gossypium hirsutum L., lines expressing both Cry1F and Cry1Ac insecticidal proteins from Bacillus thuringiensis (Bt) have been commercially available in the United States since 2005. Both Bt proteins are highly effective against tobacco budworm, Heliothis virescens (F.), and other lepidopteran pests of cotton. Although CrylAc has been available in Bt cotton since 1996, the Cry1F component is relatively new. As part of the proactive resistance management program for Cry1F/Cry1Ac cotton, a susceptibility-monitoring program is being implemented. Baseline variation in the susceptibility to Cry1F in field populations of tobacco budworm was measured. There was a three-fold variation in the amount of Cry1F needed to kill 50% of the neonates from 15 different field populations from the southern and central United States. Future variation in susceptibility of tobacco budworm populations to Cry1F or even resistance evolution could be documented based on this baseline data. A candidate diagnostic concentration was determined that may be efficiently used to identify individuals that potentially carry major alleles conferring field-relevant resistance to Cry1F before such alleles spread through field populations.

Pyrethroid Insecticide Efficacy Against Tobacco Budworm (Lepidoptera: Noctuidae) in North Carolina Flue-Cured Tobacco: Implications for Insecticide Resistance Management

Foliar applications of 3 pyrethroid insecticides were made to flue-cured tobacco and compared with Bacillus thuringiensis Berliner (Bt) bait and sprays of acephate and spinosad for control of the tobacco budworm, Heliothis virescens (F.), in 2001, 2002, and 2003. Lambda-cyhalothrin, cyfluthrin, and bifenthrin provided significant control of tobacco budworm when compared with untreated checks in all 3 yrs; however, they were generally less efficacious than the other insecticides tested. The level of control among the pyrethroids differed significantly within years but was inconsistent from year to year. The severity of tobacco budworm feeding damage was recorded for individual plants in each treatment, and damage averaged over pyrethroid treatments was 54.17% lower than the untreated control in 2001 and 79.84% lower in 2003. Pyrethroid treatments had no impact on yield of cured leaf in 2001 or 2003 compared with controls. The use of pyrethroid insecticides in flue-cured tobacco will increase the selection pressure placed on tobacco budworm populations in North Carolina. As a result, resistance to this class of insecticides may develop at an accelerated rate.

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.

Cytochrome P450 (CYP)9A1 in Heliothis virescens: the first member of a new CYP family

A novel cytochrome P450 cDNA with its complete coding sequence and part or all of the 3′ (77 nucleotides) and 5′ (87 nucleotides) non-coding sequence was isolated from the tobacco budworm, Heliothis virescens (F). The 1763 nucleotide sequence encodes a protein of 532 amino acids which includes a hydrophobic N-terminal region and the highly conserved heme binding regions typical of P450s. Low sequence similarity to other P450 sequences and the presence of a thromboxane synthase-like insertion upstream from the I helix resulted in its assignment as the first member of family 9, i.e. CYP9A1. CYP9A1 is most similar to CYP3A1 from the rat (34.7% identity), but is also similar to the insect P450s from family 6, including CYP6BIv1 from Papilio polyxenes (33.3%), CYP6A2A from Drosophila melanogaster (32.4%), CYP6A3 from Musca domestica (31.7%) and CYP6B2 from Helicoverpa armigera (30.1%). Comparative Western and Northern blot studies indicate that expression of CYP9A1 in thiodicarb selected populations of tobacco budworm is associated with insecticide resistance. The pattern of restriction fragment length polymorphism (RFLP) variation in offspring of singlepair matings demonstrated autosomal inheritance of CYP9A1 and enabled its assignment to linkage group 7. The coding region of CYP9A1 occupies no more than 10 kb in the tobacco budworm genome.

A population genetic test of selection at the molecular level.

The role of natural selection in molecular evolution has been inferred primarily by rejection of null hypotheses based on neutral theory, rather than by acceptance of specific predictions based on selection. In this report, a population genetic test of a specific prediction for selection on DNA polymorphism is presented. Pyrethroid insecticide use constitutes an experiment for which form of selection and molecular target (voltage-gated sodium channels) are both known. As predicted, differential pyrethroid selection on tobacco budworm populations generated significant geographic heterogeneity in sodium channel marker allele frequencies, compared with arbitrary loci.

Target-Site Insensitivity as the Mechanism of Resistance to Oregano phosphorus, Carbamate, and Cyclodiene Insecticides in Tobacco Bud worm Adults

Mechanisms of resistance to oregano phosphorus, carbamate, and cyclodicne insecticides were investigated in adult tobacco bud worms, Heliothis virescens (F.). Comparative studies on profenofos toxicity with or without synergists failed to demonstrate that enhanced metabolism was a major mechanism of resistance to this insecticide. Percentage of survival of several partially resistant tobacco bud worm populations at diagnostic concentrations of profenofos and methomyl was highly correlated, suggesting the same mechanism confers resistance to these insecticides. Differences between resistant and susceptible tobacco bud worms in inhibition of acetylcholinesterase by tetrachlorvinfos (7-fold), methomyl (7.6-fold), and carbaryl (4-fold) indicated that target-site insensitivity was a major mechanism of resistance to oregano phosphorus and carbamate insecticides. The high correlation of survival of field tobacco bud worm populations exposed to diagnostic concentrations of endosulfan and dieldrin suggested that the same mechanism (target-site) conferred resistance to both insecticides. Measurements of penetration of radiolabeled profenofos indicated that a decrease in insecticide uptake may be an additional resistance factor in the tobacco bud worm. Because target-site resistance to insecticides is expressed in both larvae and adults, monitoring for resistance in adults is appropriate with these insecticides.

Monitoring for Resistance to Oreganophosphorus, Carbamate, and Cyclodiene Insecticides in Tobacco Budworm Adults (Lepidoptera: Noctuidae)

A glass vial bioassay procedure was used to monitor insecticide resistance to oregano phosphorus, carbamate, and cyclodiene insecticides in field populations of adult male tobacco bud worm, Heliothis virescens (F.). These tests indicated that resistance was present in field populations in Texas, Arkansas, and Mississippi in 1992 and 1993. Diagnostic concentrations needed to distinguish susceptible tobacco bud worms from those that were heterozygous and homozygous for resistance were as follows: profenofos (10 µg per vial), methomyl (1 µg per vial), and endosulfan (1 µg per vial). The seasonal pattern of resistance was similar for all insecticides in that relative proportions of resistant genotypes peaked in mid season and declined late in the season. The occurrence of resistance was higher in 1992 than in 1993. The data presented suggest that resistance management is possible with these insecticides just as it is with pyrethroids and strategies to manage resistance should involve conservative use of all classes of insecticides for tobacco bud worm control.

Development of a Technique To Monitor Resistance to Biodegradable Insecticides in Field Populations of Tobacco Budworm (Lepidoptera: Noctuidae)

A procedure involving the use of glass vials containing insecticide was clevcloped to monitor for resistance to biodegradable insecticides among field populations of adult tobacco bud worms. Heliothis virescens (F.). These insecticides are replacing pyrethroids for the tobacco bud worm control in areas where pyrethroid resistance is a problem. Residues of profenofos, chlorpyrifos, methomyl, and endosulfan in glass vials were depleted in 2 d when they were held either in daylight or in the dark at room temperature. Residues of these compounds remained much longer (>70 d) in vials held in the freezer. The loss of toxicity was shown to mainly caused by hydrolytic degradation of the insecticide rather than to the volatilities. The addition of mineral oil or ethylene glycol did not increase the persistence of insecticide residues in glass vials; however, addition of an organic acid (benzoic or decanoic) to the vials significantly extended stability of insecticide residues. Based on these results, treating vials with combinations of insecticides plus benzoic acid and storing them in a freezer is this preferred technique if they are held for extended periods before use. The usefulness of this technique was confirmed by gas-liquid chromatographic analysis of insecticide residues and by field monitoring data.

Efficacy of Selected Commercial and Experimental Insecticides Against Late Season Populations of Beet Armyworm, Soybean Looper, and Tobacco Budworm, 1994

Abstract Three tests, each consisting of 4-5 insecticide treatments were replicated 4 times in a RCBD at the Macon Ridge Branch of the Northeast Research Station, Winnsboro, LA. Cotton was planted 1 Jul into plots 4 rows (40 inch centers) by 30 ft. Treatments for Tests 1, 2 and 3 were applied on 2, 13 and 14 Sep, respectively, with a high clearance sprayer calibrated to deliver 11.5 gal total spray/acre through Teejet X-8 hollow cone nozzles (2/row) at 46 psi. Treatment efficacy was determined by taking a 10 sweep (standard 15 inch diam net) sample from each plot. Sweep samples were usually taken 2, 4-5 and 6-7 DAT on rows 1, 2 or 3, respectively. The test areas received 0.20, 0.67 and 1.1 inches rainfall on 6, 15 and 16 Sep, respectively.

Japanese Honeysuckle (Caprifoliaceae): Newly Discovered Host of Heliothis virescens and Helicoverpa zea (Lepidoptera: Noctuidae)

Flowers of Japanese honeysuckle, Lonicera japonica Thunb., were found to support larval populations of tobacco budworm, Heliothis virescens (F.), and corn earworm, Helicoverpa zea (Boddie), in southwestern Georgia and northern Florida. However, larvae were not detected in samples taken during 1990 in southeastern Oklahoma and eastern Texas. This discovery constitutes a new host record for both H. virescens and H. zea. Studies conducted at 10 different sites in Tift County, Georgia, during 1988–1990 revealed that H. virescens populations peaked on Japanese honeysuckle during the F1 generation of April through May and again during August through September. H. zea larval populations occurred principally during August through September. Peak F1 larval populations of H. virescens on Japanese honeysuckle occurred at the same time as those on crimson clover, Trifolium incarnatum L., and wild geranium, Geranium carolinianum L. Both H. virescens and H. zea larvae were capable of developing on Japanese honeysuckle flowers in the laboratory. Although survivorship was lower, H. virescens also developed on Japanese honeysuckle leaves and berries. Cardiochiles nigriceps Viereck was the principal species parasitizing H. virescens; parasitism of H. zea was negligible and Microplitis croceipes (Cresson) was the only species detected. M. croceipes was the primary parasitoid of H. virescens and H. zea larvae collected from crimson clover. Results of this study indicate that Japanese honeysuckle is an important early season host of H. virescens and an important late-season host for both H. virescens and H. zea when overwintering populations are developing.

Influence of Planting Date on the Seasonal Abundance of Tobacco Budworms (Lepidoptera: Noctuidae) and Tobacco Aphids (Homoptera: Aphididae) on Georgia Flue-Cured Tobacco

The influence of planting date of flue-cured tobacco, Nicotiana tabacum L., on the seasonal abundance of tobacco budworms, Heliothis virescens (F.), and tobacco aphids, Myzus nicotianae Blackman, was examined in field plots in Georgia during 1987–89. Tobacco aphid population densities (aphids per plant) were influenced by yearly effects; however, tobacco budworm populations (budworms per 10 plants) were similar among the three years. A planting date (PD) effect (late March, mid-April, late April) was observed for tobacco aphids only in 1989, when higher population densities occurred in the late-planted tobacco. Planting date influenced tobacco budworm population densities in two of the three years. Significant differences in tobacco aphid populations were detected between PD's in all three years for the weekly samples in June and July, the period when seasonal aphid densities were the highest. Population peaks were higher in the mid-and late planting dates, except in 1987 when high aphid densities (3000 per plant) occurred only during the early planting date. Weekly differences in tobacco budworm populations also were detected among planting dates on many sampling dates throughout the season in all three years. Tobacco budworms occurred earliest in the early-planted tobacco, but peak densities were highest in the late-planted tobacco. Both tobacco budworm and tobacco aphid populations declined after the plants were topped (terminal floral branch removed) and a fatty alcohol sucker control was applied.

Evaluation of Pirate Against Late Season Populations of Bollworm, Tobacco Budworm and Beet Armyworm, 1992

Abstract Cotton was planted on 6 Jul with plots consisting of 4 rows (102 cm centers) × 15 m. Treatments were arranged in a randomized complete block design, replicated 4 times. Applications were made with a high clearance sprayer calibrated to deliver 93.5 liters total spray/ha through Teejet X-12 hollow cone nozzles (2/row) at 2.8 kg/cm2. Insecticide treatments were applied on 10, 14, 18, and 28 Sep against an established population of bollworms and tobacco budworms (primarily tobacco budworms). Efficacy against bollworms and tobacco budworms was determined by examining 25 squares/plot for evidence of feeding damage and the presence of larvae on each of 3 observation dates. Efficacy against beet armyworms was determined by taking 10 sweeps/plot with a standard (38 cm diameter) sweep net.

Evaluation of Selected Insecticide Mixtures Against Late Season Populations of Bollworm, Tobacco Bud-Worm and Beet Armyworm, 1992

Abstract Cotton was planted on 6 Jul with plots consisting of 4 rows (102 cm centers) x 15 m. Treatments were arranged in a randomized complete block design, replicated 4 times. Applications were made with a high clearance sprayer calibrated to deliver 93.5 liters total spray/ha through Teejet X-12 hollow cone nozzles (2/row) at 2.1 kg/cm2. Insecticide treatments were applied on 8, 11, 18, and 28 Sep against an established population of bollworms and tobacco budworms (primarily tobacco budworms). Efficacy against bollworms and tobacco budworms was determined by examining 25 squares/plot for evidence of feeding damage and the presence of larvae on each of 3 observation dates. Efficacy against beet armyworms was determined by taking 10 sweeps/plot with a standard (38 cm diam) sweep net.

Evaluation of Selected Insecticide Mixtures Against Late Season Populations of Bollworm, Tobacco Bud-Worm and Beet Armyworm, 1992

Abstract Cotton was planted on 6 Jul with plots consisting of 4 rows (102 cm centers) x 15 m. Treatments were arranged in a randomized complete block design, replicated 4 times. Applications were made with a high clearance sprayer calibrated to deliver 93.5 liters total spray/ha through Teejet X-12 hollow cone nozzles (2/row).at 2.1 kg/cm2. Insecticide treatments were applied on 8, 11, 18, and 28 Sep against an established population of bollworms and tobacco budworms (primarily tobacco budworms). Efficacy against bollworms and tobacco budworms was determined by examining 25 squares/plot for evidence of feeding damage and the presence of larvae on each of 3 observation dates. Efficacy against beet armyworms was determined by taking 10 sweeps/plot with a standard (38 cm diameter) sweep net.

Resistance to Pyrethroid, Carbamate, and Organophosphate Insecticides in Field Populations of Tobacco Budworm (Lepidoptera: Noctuidae) in 1990

Responses of tobacco budworm, Heliothis virescens (F.), to several classes of insecticides were determined using four types of laboratory bioassays. Topical application bioassays on third instars showed 13- to IS-fold resistance to cypermethrin, 7- to 12-fold resistance to profenofos, and 7- to 10-fold resistance to sulprofos in strains collected from Louisiana in 1990. A bioassay with neonate larvae showed 139- to 173-fold resistance levels to cypermethrin in the Louisiana strains. An adult vial test showed 9- to 12-fold resistance to cypermethrin. Resistance to pyrethroid, carbamate, and organophosphate insecticides was found in strains from Louisiana and Mississippi using a spray chamber bioassay. Multiple resistance to insecticides has not been reported in H. virescens since the late 1970s. Implications for control of tobacco budworm with currently available insecticides are discussed.

Influence of Transplanting Date and Tobacco Budworm (Lepidoptera: Noctuidae) Treatment Threshold Density on Flue-Cured Tobacco Quality and Yield and Secondary Pests

The influence of transplanting date and treatment thresholds for tobacco budworm, Heliothis virescens (F.), on leaf quality and yield of flue-cured tobacco, Nico-tiana tabacum L., was examined in field plots during 1987-1989. Up to six insecticide applications were needed to maintain tobacco budwonn population densities of less than one per 20 plants in the early-transplanted tobacco (late March). Fewer insecticide applications were needed to maintain this pest population density in the middle- (mid-April) and late-planted (late April) tobacco. Transplanting date and tobacco budwonn treatment threshold level (I, 2, 4, or 8 budwonns per 20 plants) significantly affected tobacco quality, yield, and budworm damage. Higher damage and lower yield and quality (grade) were observed in later-planted tobacco, on which peak tobacco bud worm populations were higher but were present for fewer weeks during the season. Treatment thresholds of four or eight bud worm larvae per 20 plants and the untreated control also resulted in significantly more damage and lower yields and grade, regardless of transplanting date. Damage due to the tobacco aphid, Myws nicotianae Blackman, also was influenced by these two factors. More tobacco aphid damage was observed in late-planted tobacco and in plots treated when tobacco budworm densities were allowed to reach four or more larvae per 20 plants. Tobacco aphid damage was significantly correlated with tobacco budwonn damage. Significant linear contrasts, and in some instances quadratic contrasts, were obtained among the budworm treatment levels for yield, quality, tobacco budworm damage, and tobacco aphid damage. Significant planting date × threshold level interactions were observed. Yield and leaf quality were not significantly different for treatment thresholds of either one or two budworms per 20 plants.

Field Evaluation of Transgenic Tobacco Containing a Bacillus thuringiensis Insecticidal Protein Gene

Six transgenic tobacco lines expressing the CryIA(b) insecticidal protein from Bacillus thuringiensis var. kurstaki HD-l were tested in 1990 to evaluate their efficacy under nonnal field conditions. Five of the six CryIA(b) lines tested kept laboratory-reared populations and natural populations of tobacco budworm, Heliothis virescens F., and tobacco hornworm, Manduca sexta L., below their respective economic threshold for the duration of the trial. Little or no economic damage from tobacco hornwonn was sustained by any CryIA(b) line and only two lines sustained significant damage from tobacco budworm. Insect control with some CryIA(b) lines was equal to or better than control by standard Orthene and Dipel treatments. In addition, data obtained suggest there may be a positive interaction between CryIA(b) protein expression within a plant and parasitism of Heliothis spp.

Pyrethroid Resistance in the Tobacco Bud worm (Lepidoptera: Noctuidae) Sterile Hybrid Strain

A sterile back cross tobacco bud worm strain (TBW-BC) of Heliothts virescens (F.) was developed before extensive use of pyrethroid insecticides. Although this strain has been maintained free of pyrethroid insecticides, most tobacco bud worm populations have been exposed to pyrethroids and have demonstrated enhanced tolerance. Our estimated LD50 (cypermethrin) for third instars was significantly lower than tobacco bud worm from Mississippi. Thus, the TBW-BC strain could be at a disadvantage if exposed to pyrethroids after release. We developed a lineage of TBW-BC strain that is resistant to cypermethrin by repeatedly back crossing TBW-BC females to resistant tobacco bud worm males and selecting for tolerance. Resistant TBW-BC strain (R-TBW-BC) (LD50,638 μg per larva) should survive field applications that would kill most wild tobacco bud worm. Back cross mortalities were consistent with polygenic inheritance, but not with monogenic inheritance. Release of RTBW-BC strain cannot change tolerance in wild tobacco bud worm, because introduced resistance alleles will be carried only by individuals that also carry the sterility trait. Resistance of sterile insects would be diluted by outcrossingto wild tobacco bud worm, but sterile insects should remain significantly more tolerant than fertile insects for at least two generations. Use of R-TBW-BC strain could reduce costs in sterile-release programs.