Comparison of Aeration and Spinosad for Suppressing Insects in Stored Wheat

Abstract

Field studies were conducted from July 2002 to January 2003 for evaluating the effects of controlled aeration and a commercial biological insecticide, spinosad, in suppressing insect populations in stored wheat. Six cylindrical steel bins were filled with newly harvested (2002 crop year) hard red winter wheat on 9 and 10 July 2002. Each bin contained 30.7 metric tons (1,100 bu) of wheat. Wheat in two bins was left untreated (control), whereas wheat in two bins was treated with spinosad, and in another two bins was subjected to aeration by using aeration controllers. Spinosad was applied to wheat at the time of bin filling to obtain a rate of 1 mg ([AI])/kg. Aeration controllers were set to run the fans when ambient air temperature fell below 23.9, 18.3, and 7.2 degrees C for the first, second, and third cooling cycles, respectively. We added 400 adults each of the rusty grain beetle, Cryptolestes ferrugineus (Stephens); lesser grain borer, Rhyzopertha dominica (F.); and red flour beetle, Tribolium castaneum (Herbst), to the grain at monthly intervals between July and October 2002. Insect density in the bins was estimated monthly by taking 3-kg grain samples from 21 locations within each bin by using a pneumatic grain sampler. No live T. castaneum or C. ferrugineus and very low densities of R. dominica (<0.008 adults per kilogram) were found in wheat treated with spinosad during the 6-mo sampling period. Density of C. ferrugineus and T. castaneum in aerated bins did not exceed two adults per kilogram (the Federal Grain Inspection Service standard for infested wheat), whereas R. dominica increased to 12 adults per kilogram in November 2002, which subsequently decreased to three adults per kilogram in January 2003. In the untreated (control) bins, R. dominica density increased faster than that of C. ferrugineus or T. castaneum. Density of R. dominica peaked at 58 adults per kilogram in October 2002 and decreased subsequently, whereas T. castaneum density was 10 adults per kilogram in October 2002 but increased to 78 adults per kilogram in January 2003. Density of C. ferrugineus increased steadily during the 6-mo study period and was highest (six adults per kilogram) in January 2003. This is the first report comparing the field efficacy of spinosad and aeration in managing insects in farm bins. Our results suggest that spinosad is very effective in suppressing R. dominica, C. ferrugineus, and T. castaneum populations in stored wheat.

Efficacy of partial treatment of wheat with spinosad against Rhyzopertha dominica (F.) adults

“…ml À1 solution resulted in a spinosad residue deposit nearly eight times higher than the tolerance level of 1.5 mg (a.i) kg À1 of grain. In real world situations, uniform coating of kernels with insecticide is rare and uneven distribution of insecticide on kernels and uneven distribution of treated kernels in a grain lot are very common (Flinn et al, 2004;Subramanyam et al, 2007). When grain is treated with an insecticide as it is being augured into the storage bins, not all kernels are treated uniformly and some kernels are not treated at all, and this may result in percentage of treated and untreated kernels to range anywhere between 10 and 100.…”

“…kg À1 , on an average, resulted in residue deposition of only 75% of the actual rates applied (Fang et al, 2002b). In 4.72 m diameter and 3.35 m high round steel bins holding 30.7 metric tons of 10.8% moisture wheat, Flinn et al (2004) reported that spinosad deposition soon after treatment at 1 mg (a.i.) kg À1 ranged from 0.40 to 0.88 mg (a.i.)…”

“…kg À1 of grain (Hertlein et al, 2011). Spinosad persists for six months up to a year on stored wheat (Fang et al, 2002a;Flinn et al, 2004;Subramanyam et al, 2007), and is extremely effective against adults of the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae), including strains resistant to organophosphates (OPs), pyrethroids, or juvenile hormone analogs (Nayak et al, 2005;Daglish and Nayak, 2006;Daglish et al, 2008).…”

“…The actual spinosad residue deposition varied in samples taken near the bin periphery and bin center and in the top, middle, and bottom portions of the grain mass. Despite these variations, the efficacy of spinosad against R. dominica was unaffected, because adults of R. dominica generally are more susceptible to spinosad than adults of other stored-product insect species (Fang et al, 2002a, b;Flinn et al, 2004;Subramanyam et al, 2007).…”

Management ofSitotroga cerealellain stored cereal grains: a review

“…Bacterial metabolites have insecticidal properties in it (Mertz & Yao 1990). Spinosad retains its insecticidal activity in stored grains from six months to one year Flinn et al 2004). It is an excellent grain protectant because its efficacy is not disrupted by grain moisture (Fang & Subramanyam 2003).…”