John S. Armstrong

Using Haplotypes to Monitor the Migration of Fall Armyworm (Lepidoptera: Noctuidae) Corn-Strain Populations from Texas and Florida

Abstract Fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), infestations in most of North America north of Mexico arise from annual migrations of populations that overwinter in southern Texas and Florida. A comparison of the cytochrome oxidase I haplotype profiles within the fall armyworm corn-strain, the subgroup that preferentially infests corn (Zea mays L.) and sorghum (Sorghum vulgare Pers.), identified significant differences in the proportions of certain haplotypes between the Texas and Florida populations. These proportional differences were preserved as the populations migrated, providing a molecular metric by which the source of a migrant population could be identified. The migratory pattern derived from this method for several southeastern states was shown to be consistent with predictions based on analysis of historical agricultural and fall armyworm infestation data. These results demonstrate the utility of haplotype proportions to monitor fall armyworm migration, and they also introduce a potential method to predict the severity of cotton crop infestations in the short term.

Structure and Distribution of a Strain-Biased Tandem Repeat Element in Fall Armyworm (Lepidoptera: Noctuidae) Populations in Florida, Texas, and Brazil

Abstract Fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), is a major economic pest throughout the Western Hemisphere. There exist two morphologically identical but genetically distinct strains (corn-strain and rice-strain) that differ in their host plant preferences. These strains can be distinguished by polymorphisms in the mitochondrial cytochrome oxidase I gene. There is also a tandem-repeat genetic element called FR that is found in large sex-linked clusters primarily in the rice strain, as characterized by sampling of fall armyworm populations in the southeastern United States. It was recently shown that the FR element is also present in Brazil, where it exhibits a similar strain-biased distribution. In this article, the analysis of FR was extended to populations in southern Texas, one of the principle overwintering locations for fall armyworm that infests the continental United States. DNA sequence analysis and an optimized polymerase chain reaction (PCR)-based method demonstrated that FR sequences are present in Texas and show the same distribution pattern as observed in Florida. The distribution of FR in Florida has remained relatively unchanged over a 4-yr period, suggestive of polymorphic equilibrium and the existence of at least partial barriers to the generation of interstrain hybrids. The implications of these findings on our understanding of interstrain mating behavior and the utility of the modified detection method to study fall armyworm populations are discussed.

Boll Weevil (Coleoptera: Curculionidae) Response to and Volatilization Rates of Grandlure When Combined with Varying Doses of Eugenol in the Extended-Life Pheromone Lure

ABSTRACT Boll weevil, Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae), trapping and pheromone quantitative analysis of extended-life pheromone lures manufactured with 0, 10, 20, and 30 mg of eugenol was conducted in the Rio Grande Valley of Texas under spring and summer conditions. Boll weevils responded positively to eugenol on one of 12 trapping weeks when densities were high, but when densities were low (<2 weevils trap-1 wk-1), there were no significant differences in captures for any dosage of eugenol offered in a standard boll weevil trap. Weekly grandlure volatilization did not differ by eugenol dose but was significantly different when evaluated over three different trapping periods and by week within trapping period due to differences in ambient temperature. The amount of grandlure that remained after 4 wk in moderate temperatures of spring was 13.1 = 0.19 mg (55.7% of original 25 mg of content) compared with 5.5 ± 0.15mg remaining (22.8% of original 25 mg content) after for 4 wk in summer heat. Weekly volatilization of grandlure for the summer trapping period was 9.8 ± 0.32 mg for the first week, declining steadily to 1.0 ± 0.09 mg by the fourth week of age. The data indicate that at high summer temperatures >30°C, accumulative grandlure loss per week may be too high, leaving too little residual grandlure to effectively attract boll weevils at the end of 3 wk of trapping. Eugenol plays no role in reserving or encouraging the release of grandlure, or in increasing boll weevil captures when boll weevil densities are low.

Kaolin particle film associated with increased cotton aphid infestations in cotton

Highly reflective white kaolin‐based particle film was sprayed on cotton, Gossypium hirsutum L. (Malvaceae), plots in south Texas during 2004 and 2005 to observe its effect on the cotton aphid, Aphis gossypii Glover (Homoptera: Aphididae). Populations of cotton aphids on the ventral surfaces of leaves in the kaolin‐treated plots were greater than in non‐treated control plots during both years. Alate cotton aphids were attracted less to white than to other pan trap colors, and parasitism by Lysiphlebus spec. (Hymenoptera: Aphidiidae) was either unaffected or greater in the kaolin‐treated plots, hence these two factors (color and parasitism) do not explain the increased infestations in the treated plots. However, mean temperatures on the ventral surfaces of kaolin‐treated cotton leaves were cooler than those of control leaves. The observed temperature difference where cotton aphids reside on cotton leaves is a potential reason for the greater infestations in the kaolin treatment plots. Our study demonstrates that applications of kaolin can exacerbate a pest infestation in cotton.

Change in Biotypic Diversity of Russian Wheat Aphid (Hemiptera: Aphididae) Populations in the United States

ABSTRACT A key component of Russian wheat aphid, Diuraphis noxia (Kurdjumov), management has been through planting resistant wheat cultivars. A new biotype, RWA2, appeared in 2003 which caused widespread damage to wheat cultivars containing the Dn4 gene. Biotypic diversity in Russian wheat aphid populations has not been addressed since 2005 when RWA2 dominated the biotype complex. Our objectives were to determine the biotypic diversity in the Central Great Plains and Colorado Plateau at regional (2010, 2011, 2013) and local (2012) levels and detect the presence of new Russian wheat aphid biotypes. Regional and within-field aphid collections were screened against Russian wheat aphidresistant wheat genotypes containing genes Dn3, Dn4, Dn6, Dn7, Dn9, CI2401; and resistant barley STARS 9301B. In 2010, all aphid collections from Texas were avirulent to the Dn4 resistance gene in wheat. Regional results revealed Dn4 avirulent RWA6 was widespread (55–84%) in populations infesting wheat in both regions. Biotypes RWA1, 2, and 3/7 were equally represented with percentages <20% each while RWA8 was rarely detected. Combining percentages of RWA1, 6, and 8 across regions to estimate avirulence to Dn4 gene revealed high percentages for both 2011 (64–80%) and 2013 (69–90%). In contrast, the biotype structure at the local level differed where biotype percentages varied up to ≥2-fold between fields. No new biotypes were detected; therefore, Dn7, CI2401, and STARS9301B remained resistant to all known Russian wheat aphid biotypes. This study documents a shift to Dn4 avirulent biotypes and serves as a valuable baseline for biotypic diversity in Russian wheat aphid populations prior to the deployment of new Russian wheat aphid-resistant wheat cultivars.

Comparisons of Boll Weevil (Coleoptera: Curculionidae) Pheromone Traps With and Without Kill Strips

ABSTRACT Boll weevil, Anthonomm grandis grandis Boheman (Coleoptera: Curculionidae), eradication programs typically equip pheromone traps with an insecticide-impregnated kill strip. These strips are intended to kill captured insects, thereby simplifying trap servicing and reducing the loss of weevils from predation and escape. However, the effectiveness of kill strips has not been extensively evaluated. We examined the influences of kill strips on weevil captures, trap servicing, and the incidences of weevil predation and trap obstruction (e.g., by spider webs). Evaluations were conducted weekly during three different production periods (pre- to early-, late-, and postseason) of cotton, Gossypium hirsutum L., to represent different environmental conditions and weevil population levels. Within each period, mean weekly captures of weevils in traps with and without kill strips were statistically similar. On average, traps with kill strips took 9 s longer to service than traps without kill strips, but statistical differences were only detected during the late-season period. Overall, the mean weekly proportion of traps with evidence of weevil predation or trap obstruction was significantly lower for traps with kill strips (0.25) than for traps without kill strips (0.37). However, this reduction in the frequency of weevil predation or trap obstruction was too small to produce a corresponding increase in the numbers of weevils captured. In light of these findings, the use of kill strips is likely unnecessary in eradication programs, but may be a consideration in situations when the numbers of deployed traps are reduced and chronic problems with weevil predation or trap obstruction exist.

Reproductive potential of field‐collected overwintering boll weevils (Coleoptera: Curculionidae) fed on pollen in the laboratory

Abstract  The reproductive potential of overwintering boll weevil, Anthonomus grandis grandis (Boheman), females collected from pheromone traps in September, November and January, fed for 1, 3, and 5 weeks on plant pollens, and then provided cotton squares, was determined in the laboratory at 27 ± 1°C, 65% RH, and a photoperiod 13 : 11 (L : D) h. Duration of pollen feeding by overwintering boll weevils did not significantly influence egg and feeding punctures, or puncture ratios (egg to total punctures) for any of the three months of parent weevil collections when provided cotton squares on a daily basis. However, punctures and puncture ratios are significantly different when comparing mean data between months of boll weevil collections. When boll weevils were provided with cotton squares daily, the pre‐ovipositional periods of female parents captured in September, November and January were 5, 9 and 14 days, respectively. The rate of eggs by females was significantly lower during November and January than September. Female parents collected in September produced a significantly higher percentage of eggs yielding adult progeny than those collected in November and January. Life table parameters indicated that net reproductive rate (Ro) of boll weevil females collected in September was 1.2‐fold higher than those collected in November and 10.7‐fold higher than those collected in January. Except for testes size, no differences in male reproductive parameters were observed during the cotton‐free period compared with males captured during mid‐cotton (June). The number of oocytes in the ovarioles and the number of oocytes containing yolk were significantly lower during September, November and January compared with June. The reproductive potential of overwintering boll weevil females collected in different months is an important consideration in determining the success of any control strategy.

Evaluation of a New Formulation of Grandlure for the Boll Weevil (Coleoptera: Curculionidae)

Grandlure, the synthesized pheromone of boll weevils (Anthonomus grandis Bohemian), consists of 2 terpene alcohols (components I and II; (+)-cis-2-isopropenyl-1 -methyl cyclobutaneethanol and cis-3,3-dimethyl-A P-cyclohexaneethanol, respectively) and 2 terpene aldehydes (components III and IV; cis-3,3-dimethyl-A1a-cyclohexaneacetaldehyde and trans-3,3-dimethyl-A1a-cyclohexaneacetaldehyde) (Tumlinson et al. 1969; Science 166:1010 -1012). The ratio of these 4 components in grandlure is « 30:40:15:15 (component l:ll:lll:IV, respectively). However, Spurgeon and Suh (2007; J. Entomol. Sci. 42:250 260) and Westbrook and Suh (2010; pp. 994 998, In Proc., Beltwide Cotton Conf.) examined the composition of pheromone released from boll weevils and reported the ratio of these 4 components in boll weevil pheromone was = 45:42:3:10. Thus, the existing commercial formulation of grandlure may not be the most effective blend for attracting boll weevils to traps. Because active and posteradication programs rely on pheromone traps to detect incipient boll weevils and to indicate the need for insecticide treatments, optimizing detection of boll weevils with traps is critically important. The objective of our study was to evaluate the attraction of boll weevils to a new experimental formulation of grandlure which matches the component ratio of pheromone produced by boll weevils. The experimental and standard formulations of grandlure were prepared by ISP Fine Chemicals (Columbus, OH). Both formulations were incorporated into lure dispensers manufactured by Plato Industries Inc. (Houston, TX) at a requested dosage of = 10 mg of pheromone per lure. The residual pheromone contents of new (0 d) and field-aged lures (1, 4, 7, 10, and 14 d) were quantified by gas chromatography (GC)

Principles and Practices of Integrated Pest Management on Cotton in the Lower Rio Grande Valley of Texas

Sustainable agriculture is ecologically sound, economically viable, socially just, and humane. These four goals for sustainability can be applied to all aspects of any agricultural system, from production and marketing, to processing and consumption. Integrated Pest Management (IPM) may be considered a key component of a sustainable agriculture system. This publication reviews recent advances in the development of IPM programs for cotton in the Lower Rio Grande Valley of Texas. We describe annual losses caused by arthropod pests in general and by specific key insect pests, briefly showed sampling of insect populations and cotton growth stages, which importance of the proper timing of scouting procedures and treatments; and economic threshold harmfulness (ETH) for optimizing control and minimizing risk from insects. We describe effectiveness of cotton insecticides; transgenically modified cotton; microbial insecticides; native, most widely-distributed and augmentative releases of beneficial insects; and cultural control techniques for cotton insects. We also show cotton diseases and weed controls. IPM is a process that considers all control options in the proportion shown in the model of a pyramid, and it can be used to demonstrate how growers might productively construct their pest management programs.

Sublethal effects of malathion on boll weevil (Coleoptera: Curculionidae) fecundity when maintained on cotton squares or artificial diet

Mated 3‐day‐old female boll weevils, Anthonomus grandis grandis Boheman, reared from field‐infested cotton (Gossypium hirsutum L.) squares were topically treated with an estimated LD50 of malathion (2 μg) to assess its effects on fecundity, oviposition, and body fat condition. Two different food sources, cotton squares and artificial diet, were assessed in malathion‐treated and nontreated (control) weevils. The LD50 caused ∼50% mortality in the square‐fed malathion treatment, but the artificial diet‐fed malathion‐treated weevils were less susceptible. LD50 survivors fed on the squares produced ≥ 9 times more chorionated eggs in the ovaries and oviposited ≥ 19‐fold more than survivors fed artificial diet, regardless of the malathion treatment. Boll weevils that survived a 2 μg LD50 malathion and also fed squares were ∼4.5‐fold leaner than diet‐fed weevils. Our findings demonstrate that non‐resistant boll weevils surviving a sublethal dose of malathion will reproduce without any delay or significant loss in fecundity, and the food source for which boll weevils are maintained when conducting these assays will directly affect the results. The significance of these findings and how they are related to the final stages of eradicating the boll weevil from the US are discussed.