Populations Of Tobacco Budworm Research Articles

Responses of Populations of the Tobacco Budworm (Lepidoptera: Noctuidae) from Northwest Mexico to Pyrethroids

Dose-mortality bioassays were begun in 1984 to determine the susceptibility of the tobacco budworm, Heliothts virescens (F.), to commonly used pyrethroids. Responses of different populations from the northwestern region of Mexico were compared with responses of two susceptible strains. The LD50’s indicated that the populations have been and are being selected for resistance to varying degrees. A population from Valle de Mexicali had the highest LD50 and resistance ratio for deltamethrin. The highest LD50’s for permethrin were obtained from 1987 populations from Valle del Yaqui and Valle de Mexicali (resistance ratios of 55.4 and 48.7, respectively). Resistance ratios from Valle del Yaqui for cypermethrin indicated that the 1987 tobacco budworm population was 32 times more resistant than the susceptible colony. Although control failures have not been reported from these areas, the dose-mortality data suggest that control failures may occur. Permethrin resistance appears to be increasing in Valle del Yaqui, Costa de Hermosillo, and Valle de Mexicali. Resistance to cypermethrin and cyfluthrin seems to be increasing in Valle del Yaqui and Valle de Mexicali. On the basis of LD50’s, deltamethrin resistance remains low except for Valle de Mexicali but should be carefully monitored.

Distribution and Abundance of Early-Season Wild Host Plants and Bollworm and Tobacco Budworm Populations (Lepidoptera: Noctuidae) in an Intensively Cropped Area of the Mid-Delta of Mississippi

An intensively cropped area of the Mississippi Delta located in Washington County, Mississippi was sampled to determine distribution and abundance of early-season wild host plants of Heliothis virescens (F.) and Helicoverpa zea (Boddie), and F1 larval populations on them. The area sampled was approximately 6.4 km square with an approximate area of 4,146 ha. Wild host plants were most numerous along roadsides, ditch and field margins, and in small (usually dry) ditches and their margins. The total area of suitable habitat for these wild hosts was estimated as 98.8 ha which represented approximately 2.4% of the total area. Species of Geranium were the most abundant wild hosts found. Helicoverpa zea and Heliothis virescens were estimated to average a combined total of 62 larvae per ha of wild host plants. These data demonstrate that experiments on the control of both pest species on wild hosts on an area-wide basis in the Delta are possible due to the confinement of these pests and their wild host plants to a relatively small area.

Resistance to Cypermethrin in First Generation Adult Bollworm and Tobacco Budworm (Lepidoptera: Noctuidae) Populations Collected as Larvae on Wild Geranium, and in the Second and Third Larval Generations

First generation (G1) larvae of the overwintered (parent) population of bollworm, Heliothis zea (Boddie), and of the tobacco budworm, H. virescens (F.), were collected in wild geranium, Geranium dissectum L. and G. carolinianum L., and then reared on artifical diet. These first generation (G1) adults were tested with a vial bioassay for resistance to cypermethrin. Survival, at the 10 p. g per vial rate, of the (G1) adult male and female bollworm was 2.9 and 5.6% and of the (G1) tobacco budworm-26 and 41.5%, respectively. First generation (G1) male and female tobacco bud worm moths that survived the 10 p.g per vial rate were mated, and the resulting second generation (G2) larvae were divided into two groups. One group was tested as third instars for resistance in a cotton terminal bud bioassay. The second group was reared to the adult stage, mated, and the resulting third generation (G3) larvae were treated as third instars with topical application of cypermethrin. In the cotton terminal bud bioassay, 65% of the (G2) larvae tested survived an application of Cymbush (cypermethrin) at its highest recommended field rate (0.09 kg [AI]/ha). LD50’s and LD50’s obtained from the topical treatment of (G3) larvae with cypermethrin were intermediate to those reported by others for tobacco budworm larvae collected from fields with control problems in the Mississippidelta. These data indicate that if the (G1) adult and (G2) larval populations in cotton in June were treated with pyrethroids, control problems would be more likely to occur later in the growing season.

Heliothis virescens (Lepidoptera: Noctuidae): Analysis of Population Responses Following Introduction of Backcrossed Insects Against Native Populations on St. Croix, U.S. Virgin Islands

A pilot test was conducted on St. Croix, U.S. Virgin Islands, to study the potential for suppressing populations of the tobacco budworm, Heliothis virescens (F.), by releasing backcrossed insects that possessed an inherited male sterility derived from the hybridization of H. subflexa (Guenee) and H. virescens . Following the release of nearly 40,000 backcrossed insects per day from 27 August to 17 December 1980, 95% of the tobacco budworms collected in February 1981 were progeny from released backcrossed females. This degree of sterility within the native tobacco budworm reduced the larval population on Bastardia viscosa (Kotb.) >80% and prevented population increase on pigeon pea ( Cajanus cajan (L.) Druce), the two most important host plants for tobacco budworm on St. Croix. The backcrossed phenotype became extinct within 5 yr of the last release, apparently because of genetic drift and selection. As the frequency of backcross declined, tobacco budworm populations returned to prerelease levels.

Variation in Resistance of Field Populations of Tobacco Budworm and Bollworm (Lepidoptera: Noctuidae) to Selected Insecticides

The pyre thyroids fenvalerate, permethrin, cypermethrin, deltamethrin, and cyfluthrin were tested against laboratory strains of the boll worm, Helios this zea (Baddie), and tobacco Budworm, Helios this viruses (F.). No differences in susceptibility were observed when the two species were exposed to the same pyre throed. LD50’s for all of the pyrethroids were significantly lower for both species than LD50’s for methomyl, methyl parathion, and profenofos. Field strains of tobacco budworms collected in Louisiana, Texas, Arizona, and Mississippiduring 1985 and 1986 exhibited low to high levels of resistance to fenvalerate (2-to 35-fold), permethrin (1- to 74-fold) and cypermethrin (2- to 9-fold) with considerable variation among strains and years. Failures of pyrethroids to provide adequate control in the field and the large reduction in susceptibility in laboratory tests against larvae from the problem areas indicate that tobacco budworm resistance to pyrethroid insecticides has reached a problem level. When tested in successive generations with fenvalerate, a highly resistant strain of the tobacco budworm exhibited a 2-fold reduction in resistance at the LD50 and a 13-fold reduction at the LD90from the F1 to the F2 laboratory generation.

Tobacco Budworm Control in Caged Cotton With a Resistant Variety, Augmentative Releases of Campoletis sonorensis, and Natural Control by Other Beneficial Species1234

A tobacco budworm, Heliothis virescens (F.), population in field cages deposited ca. 1/2 as many eggs on a nectariless-high terpenoid-hirsute line of colton (XG-31) as on a nectaried-normal terpenoid-hirsute line (M-8). Fewer small larvae developed to medium size on XG-31 than on M-8, indicating small larval mortality most likely due to the high terpenoid content. About 8 times more medium-size larvae and twice as many large larvae were present on M-8 as on XG-31 in the F1 insect generation. Releases of Campoletis sonorensis (Cameron) resulted in 81–100% parasitism of medium larvae and, thus, considerably fewer large larvae. A native parasite, Trichogramma pretiosum Riley, and a predator, Orius insidiosus (Say), also preyed heavily on the tobacco budworm population. As a result, F2 tobacco budworm larval populations did not develop in the XG-31 plots where C. sonorensis was released. The numbers of small- and medium-sized tobacco budworm larvae also were greatly reduced in the M-8 parasite release plots. The nectariless XG-31 had fewer cabbage looper, Trichoplusia ni (Hubner), eggs and larvae than the nectaried M-8, but the high terpenoid content of XG-31 did not significantly affect numbers of cabbage looper larvae.

Effects of Nectariless Cotton on Caged Populations of Campoletis sonorensis 12

Comparison of the longevity of adults of Campoletis sonorensis (Cameron) on one nectaried and 2 nectariless strains of cotton showed a reduced longevity due to lack of extrafloral nectaries. However, the effect was considerably less when floral nectaries were available (plants in bloom stage). Male longevity was less than female longevity on both nectaried and nectariless strains, and the effect of the nectariless character was greater on males than females. Releases of C. sonorensis against populations of tobacco budworm, Heliothis virescens (F.), on cotton in field cages showed that parasitism was lower on a nectariless strain than on a nectaried strain. However, rates of parasitism on both strains of cotton were relatively high, and parasites were able to maintain a generation cycle on nectariless cotton. Therefore, nectariless cotton appears to have only a slight effect on the impact of caged C. sonorensis as a parasite of the tobacco budworm.

Campoletis sonorensis: 1 Maintenance of a Population on Tobacco Budworms 2 in a Field Cage 3

Releases of 835 mated adult female Campoletis sonorensis (Cameron) at a rate of 50–100/day for 10 days against an introduced population of tobacco budworms, Heliothis virescens (F.), on cotton in a 0.4-acre field cage resulted in 85–95% parasitization of tobacco budworm larvae for ca. 2 months. As host pressure was maintained by daily releases of adult moths, C. sonorensis was eventually replaced as the major regulator of the tobacco budworm population by parasitization of host eggs by Trichogramma sp. and predation of host eggs and small larvae by Orius insidiosus (Say). The C. sonorensis population was also greatly affected by the hyperparasites Catolaccus aeneoviridis (Girault) and Ceratosmicra immaculata (Cresson); and the predator Collops vittatus (Say) consumed up to 70% of the cocoons of C. sonorensis . Nevertheless, the beneficial species markedly suppressed the tobacco budworm population throughout the experiment. Weekly average temperatures between 80 and 86°F did not appear to reduce the efficiency of C. sonorensis . The sex ratio of parasites produced in a field cage was near 1:1 as compared to 1:4 in a culture maintained in the laboratory.