Increased efficacy and extended shelf life of spinosad formulated in phagostimulant granules against Spodoptera frugiperda.

BACKGROUND: Spinosad is recommended for control of Spodoptera frugiperda (J.E. Smith) larvae; its application with phagostimulants may reduce the quantity of active ingredient required for effective pest control. Spinosad (Tracer®) was formulated in maize flour matrix granules and three field tests compared 10-100 ppm a.i. granules (equivalent to 0.24-2.4 g a.i. ha-1 ) with Tracer as an aqueous spray (200 ppm a.i.; 60 g a.i. ha-1 ), and the recommended application rates of Bacillus thuringiensis, a chemical and an untreated controls were performed. RESULTS: The 100 ppm spinosad granules resulted in similar S. frugiperda mortality compared with the chemical treatments in all three field trials, and resulted in a significantly higher maize grain yield compared with unformulated and control treatments (4141 vs. 2857 and 2407 kg ha-1 , respectively) that was similar to the chemical treatment (3778 kg ha-1 ). Bioassays of granules stored at room and cold temperatures showed that after 5 years, ∼ 70% of the original activity remained (OAR) of spinosad when formulated as granules. Nevertheless, after 9 years, efficacy was reduced (26.2% and 48.5% OAR) at both room (25 °C) and refrigerated temperatures (4 °C). CONCLUSION: Spinosad, in the granular phagostimulant formulations evaluated in this study, had advantages measured as high efficacy and long shelf life. © 2017 Society of Chemical Industry.

Differences in susceptibility and physiological fitness of Mexican field Trichoplusia ni strains exposed to Bacillus thuringiensis.

The use of different commercial Bacillus thuringiensis (Bt) products in the Bajio guanajuatense area in Mexico began 12 yr ago, and resistance to Bt in this area has been reported for Plutella xylostella (L.) The current study provides a baseline response and resistance potential to Bt in field and laboratory strains of Bajio Trichoplusia ni (Hübner). Differences in susceptibility to Bt among T. ni populations were observed. T. ni neonates collected in Romita, Guanajuato, were more susceptible to Bt than those collected in Salvatierra or San Luis de la Paz, Guanajuato. After five generations of exposure to XenTari in the laboratory, decreased susceptibility was found only in the Salvatierra insects, with an LC50 that was 2.1-fold greater than that of a Mexican laboratory strain. The XenTari-selected San Luis de la Paz strain was from 16- to 87-fold more resistant to CrylA protoxins than U.S. (US) and Mexican laboratory strains. Although CrylAb is not a component of XenTari, this strain also was significantly less susceptible to CrylAb toxin compared with a US strain, with a resistance ratio of 40.4. The larval weights and lengths, pupal lengths, and percentage of pupation were significantly lower for the Salvatierra strain than for all other strains. The relationship of T. ni susceptibilities to Bt Cry toxins and protoxins after several generations of exposure to XenTari and its similarity to P. xylostella behavior.