Laboratory and field evaluations of imidacloprid against Melanoplus sanguinipes (Orthoptera: Acrididae) on small grains.

The toxicity of imidaloprid to the migratory grasshopper, Melanoplus sanguinipes (F.), was measured in bioassays, greenhouse trials, and field trials. An LD50 of 53 and 86 ppm for the oral/topical applications of imidacloprid confirmed a low toxicity for this chemical when compared with carbofuran as a standard. However, 100% debilitation was observed at concentrations of > or = 1 ppm. Grasshoppers exhibited leg flexing, abdominal quivering, and tremors before becoming motionless and appearing dead. Knockdown was temporary with a high percentage of recovery within 1 h. Efficacy and feeding damage were determined from artificial infestations of M. sanguinipes at the 2nd, 4th, and early tillering growth stages of winter and spring wheat treated with foliar and seed treatments of imidacloprid. All rates of imidacloprid tested resulted in < 45% mortality to 4th instar and adult M. sanguinipes in the greenhouse and field. Although efficacy was low, high rates of debilitation in bioassays suggest that improved control may be gained by combining imidacloprid with insect pathogens or additional chemicals.

Action windows for optimum control of rangeland grasshoppers (Orthoptera: Acrididae).

Different assemblages of primary and secondary pest grasshopper species were found in 5 different rangeland plant communities in western North Dakota. The action window for their control (i.e., the interval when control is likely to be efficacious) with short-lived insecticides can be visualized in terms of time, grasshopper phenology, or plant phenology. Action windows ranged from 14 d duration in habitats dominated by western wheatgrass to 38 d duration in habitats dominated by needle-and-thread or by crested wheatgrass. Action windows opened 11-15 d later in rhizominous grass habitats than in bunchgrass habitats because of increased presence of late-hatching secondary pest species. In all habitat types, action windows closed primarily in response to imminent oviposition by a ubiquitous primary pest species, Melanoplus sanguinipes (F.). In all habitat types, action windows tended to open during seed development of 2 common and conspicuous grasses, needle-and-thread and green needlegrass. No such consistent indicator for closure of action windows was detected.

Field assessment of Beauveria bassiana (Balsamo) vuillemin and potential synergism with diflubenzuron for control of savanna grasshopper complex (Orthoptera) in Mali.

In large-scale field trials in Mali, formulated conidia of Beauveria bassiana (Balsamo) Vuillemin strain GHA were tested against unconfined grasshopper populations in field plots of 10 ha each. The trials compared B. bassiana conidia formulated in a mineral oil carrier, formulated diflubenzuron, a combination of B. bassiana plus formulated diflubenzuron, and fenitrothion. A total of 30 different species of grasshoppers occurred in the experimental plots, of which 3 were dominant in all plots, namely, Cryptocatantops haemorrhoidalis (Krauss), Acrotylus blondeli (Saussure), and Hieroglyphus daganensis (Krauss). The density of grasshopper populations in the plots was determined by the number of grasshoppers counted in 0.1-m2 rings laid out in repeated transects. All treatments significantly reduced the grasshopper densities in the experimental plots compared to the untreated controls. After 14 days posttreatment the grasshopper populations decreased by 38.1% in plots treated with B. bassiana alone, 29.4% in plots treated with diflubenzuron alone, and 55.6% in plots treated with the B. bassiana plus diflubenzuron. Effects of the diflubenzuron-B. bassiana mixture were additive and not synergistic. In the fenitrothion plots, after a drop of 95.5% within the first 48 h after the treatment, the grasshopper population steadily increased at a rate of 12.4% per day for the remainder of the 14-day period, whereas densities in the other treated plots continued to decrease. These trials suggest that B. bassiana, with or without a diflubenzuron additive, exerts a continuous effect over a prolonged period.