Phosphine resistance in Tribolium castaneum and Rhyzopertha dominica from stored wheat in Oklahoma.

Phosphine gas, or hydrogen phosphide (PH3), is the most common insecticide applied to durable stored products worldwide and is routinely used in the United States for treatment of bulk-stored cereal grains and other durable stored products. Research from the late 1980s revealed low frequencies of resistance to various residual grain protectant insecticides and to phosphine in grain insect species collected in Oklahoma. The present work, which used the same previously established discriminating dose bioassays for phosphine toxicity as in the earlier study, evaluated adults of nine different populations of red flour beetle, Tribolium castaneum (Herbst), and five populations of lesser grain borer, Rhyzopertha dominica (F.) collected from different geographic locations in Oklahoma. One additional population for each species was a laboratory susceptible strain. Discriminating dose assays determined eight out of the nine T. castaneum populations, and all five populations of R. dominica, contained phosphine-resistant individuals, and highest resistance frequencies were 94 and 98%, respectively. Dose-response bioassays and logit analyses determined that LC99 values were approximately 3 ppm for susceptible and 377 ppm for resistant T. castaneum, and approximately 2 ppm for susceptible and 3,430 ppm for resistant R. dominica. The most resistant T. castaneum population was 119-fold more resistant than the susceptible strain and the most resistant R. dominica population was over 1,500-fold more resistant. Results suggest a substantial increase in phosphine resistance in these major stored-wheat pests in the past 21 yr, and these levels of resistance to phosphine approach those reported for other stored-grain pest species in other countries.

Effects of phosphine and methyl bromide fumigation on the volatile flavor profile and sensory quality of dry cured ham.

In separate experiments, randomized complete block designs with three replications were utilized to evaluate the effects of phosphine (PH(3)) (0, 200 and 1000ppm for 48h) and methyl bromide (MB) (0, 4, 8, 16, and 32mg/L for 48h) fumigation concentration on the volatile flavor compound concentrations in dry cured ham. Minimal differences existed (P>0.05) in the presence and concentration of aroma active compounds in both PH(3) and MB fumigated hams but sulfur and oxidation compounds were more prevalent (P<0.05) in the fumigated treatments when compared to the control. As phosphine fumigation concentration increased, the residual concentration of phosphine also increased in the hams (P<0.05), but all samples contained levels that are lower than the legal limit of phosphine allowed in stored food products (0.01ppm) in the United States. A triangle test (n=56) indicated that consumers could not discriminate (P>0.75) between the control hams and those that were fumigated with PH(3). Minimal aroma/flavor differences existed among MB, PH3 and control hams, and dry cured ham that was fumigated with PH(3) was safe for consumption based on residual phosphine concentrations in the meat tissue.

Sulfuryl fluoride fumigation effects on the safety, volatile composition, and sensory quality of dry cured ham.

A randomized complete block design with three replications was utilized to evaluate the effects (P<0.05) of various fumigation concentrations of sulfuryl fluoride (SF) (0, 12, 24, 36 and 72 mg/L) on the fluoride, sulfuryl fluoride, and volatile flavor compound concentrations in dry cured ham. Fluoride and SF concentrations increased (P<0.05) in dry cured hams as SF fumigation concentration increased, but all samples contained fluoride and SF concentrations below the legal limits of 20 and 0.01 ppm, respectively. Minimal differences existed (P>0.05) in the presence and concentration of aroma active compounds, but oxidation compounds were slightly more prevalent (P<0.05) in the 72 mg/ml treatment when compared to the control. A triangle test (n=54) indicated that consumers could not discern (P>0.75) between hams that were fumigated with SF at 0 and 36 mg/ml. This study revealed that there were minimal aroma/flavor differences among the ham treatments between 0 and 36 mg/ml, and that dry cured ham that was fumigated with SF was safe and met legal requirements for consumption.