Antonio P. Terán-Vargas

Susceptibility of isofamilies of Spodoptera frugiperda (Lepidoptera: Noctuidae) to Cry1Ac and Cry1Fa proteins of Bacillus thuringiensis.

Abstract. The fall armyworm, Spodoptera frugiperda (J. E. Smith), is one of the most important insect pests on the American continent. Its control has relied primarily on multiple applications of insecticides that can amount to 1,000 g of active ingredient per hectare on some of approximately 30 crops the insect damages. The use of genetically engineered crops that express Bacillus thuringiensis (Bt) Berliner toxins, Bt-corn, Zee meys L.; and Bt-cotton, Gossypium hirsutum L.; are other ways to control this insect. However, fall armyworm is one of the Lepidoptera species least susceptible to Bt proteins, and a case of high tolerance to Bt-corn has already being reported. We found the susceptibility to Cry1Ac and Cry1Fa proteins of Bt in 133 isofamilies from five regions of three countries was similar to the susceptibility of two Bt-susceptible laboratory colonies to these proteins. Four isofamilies from Puerto Rico were very tolerant to Cry1Fa and not so tolerant to Cry1Ac. Two of the four isofamilies were backcrossed with a Bt-susceptible laboratory colony and their progeny was as susceptible to both Bt proteins as was the Bt-susceptible colony, indicating that resistance to Bt is a recessive trait.

Plant Host Effect on the Development of Heliothis virescens F. (Lepidoptera: Noctuidae)

Abstract Heliothis virescens F. is an important polyphagous pest that can develop on >100 plant species, including 20 economic crops. Populations of this insect are believed to be locally maintained on a few crops and weed hosts in Washington County, MS. To find the intrinsic value of these plants for the development of H. virescens populations, we fed different laboratory and wild colonies with fresh and lyophilized plant tissue under a constant temperature. Development time of this insect under laboratory conditions varied up to 10 d between plant hosts and was dependent on the type of plant tissue provided: fresh or lyophilized. Life table parameters such as net reproductive rate, finite rate of increase, and generation time indicated that Trifolium repens, a wild host growing around agricultural fields year round, could be one of the most suitable local plant hosts for the development of H. virescens. Two species of Geranium, previously reported as the source of the first H. virescens generation in the region, had lower intrinsic value as a food source than did T. repens. Gossyipium hirsutum, perhaps the most important crop source of H. virescens in the region, produced low net reproductive rate and finite rate of increase parameters. Sampling conducted in agricultural fields during 2006 and 2007 found no larvae on the above mentioned wild hosts as it was previously reported. Results indicated that H. virescens populations in this region were not supported by the wild plant species growing around agricultural fields during the time when the survey took place.

Densities of Heliothis virescens and Helicoverpa zea (Lepidoptera: Noctuidae) in Three Plant Hosts

Abstract Large numbers of field-collected tobacco budworms Heliothis virescens L., and/or bollworms Helicoverpa zea (Boddie) (heliothines) might be difficult to obtain depending upon host plants available to the insects. Of the >95 cultivated and wild plants that have been identified as their hosts, some are highly attractive to these insects, some are also widely available and of those, some could be used to collect large numbers of both insect species. However, the reliability of these plants in space and time in providing abundant samples of larvae and/or moths is not well understood. We studied naturally-occurring heliothine populations over a 3-year period in 2 different geographic locations in plots of garbanzo bean (Cicer arietinum L.), upland cotton (Gossipium hirsutum L.), and velvetleaf (Abutilon theophrasti Medikus) finding that garbanzo bean produced significantly higher numbers of tobacco budworm and bollworm larvae and adults as compared to the other 2 plant species. Tobacco budworm larvae were found in at least 1 host plant (primarily garbanzo) all the years in both locations while bollworm larvae were not. Field moth emergence represented ≤10% of its larval densities and abiotic factors made a difference on moth emergence between years. When large numbers of both insects are needed for field or laboratory studies, garbanzo bean offers a clear advantage over cotton or velvetleaf to obtain collections of heliothines.

Bacillus thuringiensis Cry1Ac resistance frequency in tobacco budworm (Lepidoptera: Noctuidae).

ABSTRACT The tobacco budworm, Heliothis virescens (F.) (Lepidoptera Noctuidae), is one of the most important pests of cotton, Gossypium hirsutum L., that has become resistant to a wide range of synthetic insecticides. Cry1Ac-expressing cotton has proven its effectiveness against this insect since its introduction in North America in 1996. However, the constant exposure of tobacco budworm to this protein toxin may result in the development of resistance to it. To estimate the frequency of alleles that confer resistance to a 1.0 µg of Bacillus thuringiensis Cry1Ac diagnostic concentration in field-collected insects, the second generation (F2) of 1,001 single-pair families from seven geographical regions representing 2,202 alleles from natural populations was screened in 2006 and 2007 without finding major resistant alleles. Neonates of 56 single-pair families were able to develop to second instar on the diagnostic concentration in the initial screen, but only seven of these lines did so again in a second confirmatory screen. Minor resistance alleles to Cry1Ac may be quite common in natural populations of H. virescens. Our estimated resistance allele frequencies (0.0036 – 0.0263) were not significantly different from a previously published estimate from 1993. There is no evidence that H. virescens populations have become more resistant to Cry1Ac.

Baseline Susceptibility of Tobacco Budworm (Lepidoptera: Noctuidae) to Cry1F Toxin from Bacillus thuringiensis

Abstract 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 Cry1Ac 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.

Maize Pests in Mexico and Challenges for the Adoption of Integrated Pest Management Programs

Mexico is the fifth largest maize producer and the area of origin and domestication of this crop. Mexicos 6.8 million hectare annual production of maize represents 30% of its total domestic agricultural production and 6.6% of the countrys arable land. However, Mexicos average yield of 3.17 tons per hectare is 38% below the worlds average. Although maize is a major crop globally, it is typically not grown under modern or comprehensive integrated pest management (IPM) programs aimed at minimizing economic damage and lowering environmental and health risks. Pest management in commercial maize in Mexico continues to rely primarily on chemical control using conventional synthetic insecticides. Approximately 3,000 tons of active ingredient per year are used to combat the single most important pest, the fall armyworm ( Spodoptera frugiperda Smith), followed by the corn earworm ( Helicoverpa zea Boddie) and the black cutworm ( Agrotis ipsilon (Hufnagel)). Mexican farmers have successfully adopted IPM programs for many crops, but IPM is not common in maize crops. Although different components and elements have been identified, most of the information on maize pests and IPM in Mexico has been published in technical bulletins of a reduced regional scope or in difficult-to-access reports, generally describing laboratory screenings, preliminary field evaluations, or listing technical recommendations but rarely including products and practices that growers actually use. This report provides up-to-date information on the common pests in the main maize-growing areas of Mexico from experts in the field. Updated information on maize pest population dynamics and control has been gathered from agricultural professionals directly involved in maize crop protection. This critical information, not readably available for Mexican production systems, is intended to help researchers, government officials, and industry specialists in making decisions regarding time and resource allocations in the design and implementation of IPM techniques, practices, and programs for Mexican maize.

Biological Effectivity of Insecticides to Control the Agave Weevil, Scyphophorus acupunctatus Gyllenhal (Coleoptera: Curculionidae), in Mexico

Abstract. Scyphophorus acupunctatus Gyllenhal causes economic losses to plants of the Agavaceae and Dracaenaceae families and, recently, in commercial plantations of nardo, Polianthes tuberosa L. Synthetic insecticides are the main controls, but these pesticides may not be effective, because larvae and adults are frequently found feeding in the interior of the “ball” of agave plants, far from the reach of the insecticide. The efficacy of insecticides to control this pest is unknown. In this study, we evaluated the effectiveness of synthetic insecticides of different toxicological groups to control S. acupunctatus. The experimental design was completely randomized. The number of dead adults was analyzed using a nonparametric variance of Kruskal Wallis. The percentages of biological effectiveness of insecticides in each bioassay were obtained by using the Abbott formula. Malathion, endosulfan, methomyl, and fipronil showed high biological efficacy. Conversely, cypermethrin, lambda-cyhalothrin, deltamethrin, and betacifluthrin, of constant use in Tamaulipas to control S. acupunctatus, produced a minor effect similar to the nontreated check. However, although some insecticides were effective, it is recommended they be rotated with insecticides with different modes of action or in conjunction with other controls such as food attractants, entomopathogenic fungi and nematodes, and aggregation pheromones, to obtain better control of S. acupunctatus and prevent development of resistance to insecticide.

Offspring from Sequential Matings between Bacillus thuringiensis-Resistant and Bacillus thuringiensis-Susceptible Heliothis virescens Moths (Lepidoptera: Noctuidae)

ABSTRACT The tobacco budworm, Heliothis virescens (F.) (Lepidoptera: Noctuidae), is an economically important pest of the Americas. Females of this species copulate multiple times during their lifetimes, and the presence of sperm from multiple males inside them could allow for a diversity of paternal genotypes in the offspring, unless there was complete precedence of sperm from the first mating. if a female copulates with a male that is insecticide-susceptible and another male that is insecticide-resistant, her progeny could vary in their resistance phenotypes. In some cases, this could impact the evolution of insecticide resistance in a population. We designed a series of experiments to determine whether Bacillus thuringiensis susceptibility is maintained when an H. virescens female that is homozygous for a genetically recessive form of B. thuringiensis resistance copulates with a Cry1Ac-susceptible and a Cry1Ac-resistant males. During the lifetime of double-copulated females, a proportion of F1 progeny were Cry1Ac-resistant. This indicates that when a B. thuringiensis-resistant H. virescens female copulates with two males, with one male being resistant to Cry1Ac, some of the progeny will carry resistance to this insecticide. Due to the polyandrous nature of this species, the above-mentioned scenario is not unrealistic; therefore, results from this study may help understand and manage the evolution of B. thuringiensis-resistance in field populations.

Incidence of Heliothis virescens on garbanzo varieties in northwestern Mississippi.

Abstract. The tobacco budworm, Heliothis virescens F., is one of the most important insect pests of cotton, Gossypium hirsutum L., and other crops. In recent years tobacco budworm has been successfully controlled with Bacillus thuringiensis-expressing cottons but might acquire resistance to this bacterium insecticide. To test its susceptibility to B. thuringiensis, a large number of tobacco budworms should be evaluated. However, obtaining large numbers of this pest has proven difficult in recent years. Varieties of garbanzo, Cicer arietinum L., one of the most preferred hosts were tested against tobacco budworm in the field. Sierra, C-104, and Annigeri varieties that can harbor ≥10 late-instar tobacco budworm larvae per meter of row and can withstand the biotic and abiotic conditions of northwestern Mississippi, were identified as good hosts for tobacco budworm. This information is of value for obtaining sufficient samples of tobacco budworms for multiple purposes and can serve as a baseline for evaluating varieties of garbanzo for commercial purposes.

Incidence of Heliothis virescens1 on Garbanzo2 Varieties in Northwestern Mississippi

Abstract. The tobacco budworm, Heliothis virescens F., is one of the most important insect pests of cotton, Gossypium hirsutum L., and other crops. In recent years tobacco budworm has been successfully controlled with Bacillus thuringiensis-expressing cottons but might acquire resistance to this bacterium insecticide. To test its susceptibility to B. thuringiensis, a large number of tobacco budworms should be evaluated. However, obtaining large numbers of this pest has proven difficult in recent years. Varieties of garbanzo, Cicer arietinum L., one of the most preferred hosts were tested against tobacco budworm in the field. Sierra, C-104, and Annigeri varieties that can harbor ≥10 late-instar tobacco budworm larvae per meter of row and can withstand the biotic and abiotic conditions of northwestern Mississippi, were identified as good hosts for tobacco budworm. This information is of value for obtaining sufficient samples of tobacco budworms for multiple purposes and can serve as a baseline for evaluating varieties of garbanzo for commercial purposes.