Mohamed A. Latheef

Effect of emamectin benzoate on mortality, proboscis extension, gustation and reproduction of the corn earworm, Helicoverpa zea

Abstract Newly emerged corn earworm adults, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) require a carbohydrate source from plant or other exudates and nectars for dispersal and reproduction. Adults actively seek and forage at feeding sites upon eclosion in the habitat of the larval host plant or during dispersal to, or colonization of, a suitable reproductive habitat. This nocturnal behavior of H. zea has potential for exploitation as a pest management strategy for suppression using an adult feeding approach. This approach entails the use of a feeding attractant and stimulant in combination with a toxicant that when ingested by the adult will either reduce fecundity/fertility at sub-lethal dosages or kill the adult. The intent of this study was to assess reproductive inhibition and toxicity of emamectin benzoate on H. zea when ingested by the adults when mixed in ppm active ingredient (wt:vol) with 2.5 M sucrose as a feeding stimulant. Because the mixture has to be ingested to function, the effect of emamectin benzoate was also evaluated at sub-lethal and lethal concentrations on proboscis extension and gustatory response of H. zea in the laboratory. Feral males captured in sex pheromone-baited traps in the field were used for toxicity evaluations because they were readily available and were more representative of the field populations than laboratory-reared adults. Laboratory-reared female moths were used for reproduction effects because it is very difficult to collect newly emerged feral females from the field. Emamectin benzoate was highly toxic to feral H. zea males with LC50 values (95% CL) being 0.718 (0.532–0.878), 0.525 (0.316–0.751), and 0.182 (0.06–0.294) ppm for 24, 48 and 72 h responses, respectively. Sub-lethal concentrations of emamectin benzoate did not significantly reduce proboscis extension response of feral males and gustatory response of female H. zea. Sublethal concentrations of emamectin benzoate significantly reduced percent larval hatch of eggs and mating frequency of female H. zea. Larval survival to the pupal stage was also significantly reduced by ingestion of emamectin benzoate by female H. zea. These data suggest that emamectin benzoate is a useful toxicant in an attract-and-kill control strategy against H. zea. Field studies are warranted to validate the results reported in this study.

Aerial electrostatic-charged sprays for deposition and efficacy against sweet potato whitefly (Bemisia tabaci) on cotton.

BACKGROUND The efficacy of aerial electrostatic-charged sprays was evaluated for spray deposit characteristics and season-long control of sweet potato whitefly (SWF), Bemisia tabaci Genn. biotype B (aka B. argentifolii Bellows & Perring), in an irrigated 24 ha cotton field. Treatments included electrostatic-charged sprays at full and half active ingredient (AI) label rate, uncharged sprays and conventional sprays applied with CP nozzles at full label rate with several different insecticides. RESULTS Spray droplet size was significantly smaller for electrostatic-charged sprays than for conventional sprays in top- and mid-canopy locations. The seasonal mean numbers of viable eggs and live large nymphs on cotton treated with electrostatic-charged sprays were comparable with those on cotton treated with conventional applications. Lethal concentration (LC(50)) for adults for electrostatic-charged sprays was comparable with that for conventional sprays. CONCLUSION The amenability of electrostatic-charged sprays to a wide array of pesticides with different chemistries should be a useful tool in combating insect resistance. Results reported here suggest that the potential exists for obtaining increased efficacy against whiteflies using an electrostatic spray charging system, and that additional research will be required to improve charge-to-mass (Q/M) ratio in order to increase deposition of pest control materials to the lower surfaces of cotton leaves where the whiteflies reside.

Transmission of Claviceps africana Spores from Diseased to Non-Infected Sorghum by Corn Earworm Moths, Helicoverpa zea

ABSTRACT The potential of corn earworm moths Helicoverpa zea, an important pest of sorghum in Texas, as a passive vector of sorghum ergot, Claviceps africana was assessed. Laboratory-reared (females and males) and field-moths trapped in sex pheromone traps were confined in screen cages with potted male-sterile sorghum line AT×623 that had been artificially infected with sorghum ergot and was producing massive amounts of honeydew that contained spores of the fungus. In the cages, moths were observed feeding on the honeydew. When laboratory-reared moths contaminated with C. africana spores were released for 12 or 48 h in cages containing healthy greenhouse- or field-grown male-sterile sorghum plants at anthesis, the levels of ergot severities on the panicles ranged from 0.5–90%, per panicle. The levels of ergot infection on greenhouse- and field-grown AT×623 exposed to ergot contaminated field-trapped males for 48 h ranged from 0–81.7%. Mean external contamination of laboratory-reared and field-trapped moths placed in a soapy wash was 1.4 × 105 and 4.7 ×104 conidia/ml, respectively. This study demonstrated that contaminated adult corn earworm could transmit the sorghum ergot from diseased to healthy panicles when environmental conditions are favorable for infection. Thus, migrating moths and other highly mobile pest species have the potential to transport C. africana over relatively large distances.

Mortality and reproductive effects of ingested spinosad on adult bollworms.

BACKGROUND Upon emergence from their pupal cells, bollworm, Helicoverpa zea (Boddie), adults actively seek and feed on plant exudates before they disperse and reproduce on suitable host plants. This nocturnal behavior of the bollworm may be exploited as a pest management strategy for suppression of the insect by using an attractant/stimulant mixed with an insecticide to induce feeding to cause adult mortality or reproductive reduction/inhibition. This study aimed to determine in the laboratory whether or not spinosad when mixed with sucrose solution as a feeding stimulant and ingested by bollworm could influence mortality and reproduction of the insect. RESULTS Sublethal concentrations of spinosad fed to laboratory-reared females confined with males significantly reduced percentage hatch of eggs at 0.1 mg L(-1), and it was reduced to near zero at 2.5 mg L(-1) when compared with females fed 2.5 M sucrose solutions only. The lethal concentration (LC(99)) for males captured from the field in sex-pheromone-baited traps was 73 mg L(-1) for 24 h response. Proboscis extension response was not inhibited significantly even at 10 g L(-1). In spite of a 137-fold increase in lethal dose concentration, spinosad did not inhibit feeding. CONCLUSION A detailed study of laboratory-reared and field-collected bollworm adults relative to mortality and reproduction after ingestion of spinosad indicates that spinosad would be useful in an attract-and-kill strategy to control the insect when mixed with a feeding attractant/stimulant. Field validation of the data is warranted.

Effect of Hexaflumuron on Gustation and Reproduction of Adult Boll Weevil

Abstract. Hexaflumuron was evaluated for effects on gustatory response and reproduction of boll weevil, Anthonomus grandis grandis Boheman, captured in pheromone-baited traps. Hexaflumuron is an insect-growth regulator that inhibits chitin synthesis and disrupts insect cuticle formation during molting. The intent was to determine the effect of hexaflumuron mixed in ppm active ingredient (weight:volume) with 10% sucrose as a feeding stimulant on gustation and reproduction of boll weevil. Regardless of concentrations, weevils captured in pheromone-baited traps in the fall ingested significantly more hexaflumuron than those captured in the spring. Seasonal mean amount of hexaflumuron ingested by the weevil decreased significantly with greater concentrations (adjusted R2 = 0.82). At 5 and 25 ppm, hexaflumuron significantly depressed gustatory response for falland spring-captured boll weevils, respectively. Hexaflumuron at 5 and 25 ppm significantly depressed oviposition and larval hatch, respectively, for both springand fall-captured weevils. However, reduction in larval hatch was minimal. Data suggest that the use of hexaflumuron as a toxicant for suppression of boll weevil when ingested is limited because of inhibitory gustatory response and minimal reduction in larval hatch. However, this method of application used for hexaflumuron may be important for other insecticides to determine effectiveness on mortality and reproduction of weevils.

Laboratory Evaluation of Novaluron for Toxicity to Nymphal Instars of Field-Collected Southern Green Stink Bug on Cotton

The efficacy of novaluron (Diamond™ 0.83 EC) on cotton, Gossypium hirsutum L., against nymphs of different instars of field-collected southern green stink bug, Nezara viridula (L.), was investigated in a spray chamber using two nozzles, 650033 and 8002E. The nozzles delivered rates of 18.7 and 46.7 L/ha, respectively, of total water-based spray. Novaluron was applied at 0.0218, 0.0436 and 0.0654 kg active ingredient (AI) rates per ha. The 8002E nozzle produced significantly larger droplets, increased droplet density and increased spray coverage compared to the 650033 nozzle. Regardless of dosage and spray rate, the age of nymphal instars significantly influenced mortality. Mortality of small nymphs (2nd instars) was significantly greater than that of either 3rd- or 4th-instar nymphs. When novaluron was applied at 0.0654 and 0.0872 kg AI per ha with or without crop oil concentrate, the deposit from the 8002E nozzle significantly increased mortality of 3rd-instar nymphs; however, neither dosage nor addition of crop oil concentrate increased mortality of 3rd-instar nymphs. Novaluron did not cause a great amount of mortality of 4th-instar nymphs. This study suggests that application of novaluron should be directed at 2nd-instar nymphs to maximize efficacy for control of southern green stink bug on cotton and that applications that produce deposits with increased droplet size and density on plants might increase efficacy.

Toxicity by Glass-Vial Bioassay of Selected Pyrethroid and Organophosphate Insecticides to Adult Brown Stink Bugs (Hemiptera: Pentatomidae) from Central Texas

Abstract. Brown stink bug, Euschistus servus (Say), has greatly increased in numbers in the Brazos Valley in Central Texas and in many other areas of the Cotton Belt, and has become a major pest of cotton, Gossypium hirsutum L., and other crops including pecans, Carya illinoensis (Wangenh.) K. Koch. Use of insecticides is among the most important of the limited control options available against this pest. Glass-vial bioassays were used to evaluate the toxicity of selected synthetic pyrethroid and organophosphate insecticides to adult brown stink bug captured in blacklight traps. A comparison was also made of toxicity of &lgr;-cyhalothrin to brown stink bug collected directly from the field to those captured in blacklight traps. Lethal concentration value (LC50) (upper and lower 95% confidence limits) for dicrotophos for 24-hour response, 0.30 (0.24–0.37) µg per vial, was significantly less compared to acephate with an LC50 of 1.38 (1.01–1.81) µg per vial and chlorpyrifos with an LC50 of 5.00 (4.27–5.67) µg per vial. Dicrotophos was five- and 17-fold more toxic to brown stink bug than acephate and chlorpyrifos, respectively. The order of toxicity to brown stink bug for synthetic pyrethroids was: bifenthrin = zeta-cypermethrin = &ggr;-cyhalothrin > &lgr;-cyhalothrin > cypermethrin. LC50 values ranged from 0.27 (0.18–0.51) for bifenthrin to 1.35 (1.01–1.90) µg per vial for cypermethrin, a five-fold difference. LC50 values for brown stink bugs collected from the field or captured in blacklight traps were not significantly different which suggests that brown stink bugs captured in blacklight traps may be used for insecticide bioassays. Data presented are useful for selecting insecticides for control and establishing baselines to monitor development of resistance of brown stink bugs to insecticides in the Brazos Valley of Central Texas.

Remote Sensing Evaluation of Two-spotted Spider Mite Damage on Greenhouse Cotton

The objective of this study was to evaluate a ground-based multispectral optical sensor as a remote sensing tool to assess foliar damage caused by the two-spotted spider mite (TSSM), Tetranychus urticae Koch, on greenhouse grown cotton. TSSM is a polyphagous pest which occurs on a variety of field and horticultural crops. It often becomes an early season pest of cotton in damaging proportions as opposed to being a late season innocuous pest in the mid-southern United States. Evaluation of acaricides is important for maintaining the efficacy of and preventing resistance to the currently available arsenal of chemicals and newly developed control agents. Enumeration of spider mites for efficacy evaluations is laborious and time consuming. Therefore, subjective visual damage rating is commonly used to assess density of spider mites. The NDVI (Normalized Difference Vegetation Index) is the most widely used statistic to describe the spectral reflectance characteristics of vegetation canopy to assess plant stress and health consequent to spider mite infestations. Results demonstrated that a multispectral optical sensor is an effective tool in distinguishing varying levels of infestation caused by T. urticae on early season cotton. This remote sensing technique may be used in lieu of a visual rating to evaluate insecticide treatments.

Toxicity of Selected Acaricides in a Glass-vial Bioassay to Twospotted Spider Mite (Acari: Tetranychidae)

Abstract. Twospotted spider mite, Tetranychus urticae Koch, feeds on epidermal cells of foliage, destroys photosynthetic cells, and reduces yield, fiber quality, and seed germination of cotton, Gossypium hirsutum L. With a short life cycle, prolific fecundity, an arrhenotokous reproduction, and an ability to expeditiously digest and detoxify xenobiotics, twospotted spider mite has the propensity to develop resistance to insecticides. Despite mobility, small size, and difficulties associated with handling of twospotted spider mites, this study demonstrated that the 20-ml glass-vial bioassay is a useful technique to evaluate contact toxicity of acaricides against adult mites in a laboratory. A colony of twospotted spider mites was maintained on pinto beans, Phaseolus vulgaris L. in a greenhouse. Abamectin with LC50 (95% CL) of 0.014 (0.01–0.02) µg per vial was 1,006 time more toxic than spiromesifen with a LC50 of 14.086 (7.592–42.371) µg per vial. The LC50 values of spiromesifen and propargite were comparable. Bifenazate was 10 times more toxic than dicofol to twospotted spider mite. The order of toxicity of acaricides tested against twospotted spider mite adults was abamectin > bifenazate > dicofol > propargite = spiromesifen. These data are useful for developing baseline contact toxicity for adult twospotted spider mite and monitoring tolerance to acaricides used on cotton in Central Texas.

Toxicity of Selected Insecticides and Insecticide Mixtures in a Glass-Vial Bioassay of Southern Green Stink Bug (Hemiptera: Pentatomidae) from Central Texas

Abstract. The southern green stink bug, Nezara viridula (L.) (Heteroptera: Pentatomidae), is cosmopolitan in distribution and feeds on a multitude of food and fiber crops. It induces abscission of bolls of cotton, Gossypium hirsutum L., and reduces seed cotton yield, gin-turnout, and fiber quality. Also, the bug vectors bacterial and fungal pathogens causing necrosis of the locule and rotting the bolls. Control options are mostly dependent upon and limited to the use of insecticides. Data are needed to assess the toxicity of currently available insecticides and develop baseline mortality data to monitor resistance of the insect to insecticides in Central Texas. We studied the toxicity of selected organophosphate and pyrethroid insecticides in a glass-vial bioassay to adult southern green stink bugs captured in blacklight traps. Dicrotophos was six times more toxic than acephate to southern green stink bug. Toxicity of acephate and chlorpyrifos was comparable. The order of toxicity of pyrethroids to southern green stink bug was &ggr;-cyhalothrin > zeta-cypermethrin > &lgr;-cyhalothrin > Cypermethrin > bifenthrin. Mixtures of technicalgrade active ingredients were 4- to 7.5-fold more toxic to southern green stink bug compared to commercially-formulated insecticides. The lesser efficacy of the commercial formulations suggests the active ingredients used in the mixtures failed to potentiate, probably because of lack of additivity or synergism in the composition of active ingredients in the formulations. The inert and other ingredients in the formulations may have played a part as well.