Degradation of fipronil (Termidor) in aqueous solution stored in polyethylene tanks exposed to sunlight or shade.

Pest Management Professionals commonly use polyethylene or fiberglass tanks for mixing and applying termiticides. We investigated the stability of fipronil (Termidor SC) (0.06%, 0.09% and 0.125% active ingredient) in aqueous solutions stored in polyethylene tanks under sun and shade for 2 week. Chemical analysis of tank-mixed solutions sampled at 0, 24, 48, 72, 168 and 336 h indicated that fipronil remained stable. Our data indicated that polyethylene tanks prevent fipronil from photodegradation and these tanks can be safely used for short term storage (up to 2 week) of liquid termiticides.

Stability of imidacloprid (Premise 75) in a tank-mixed aqueous solution when stored in shade or sunlight.

Polyethylene tanks are commonly used by pest management professionals to mix and apply termiticides. These termiticides are susceptible to rapid photolysis and the ability of application tanks to filter sunlight has been questioned. We investigated the stability of imidacloprid (Premise 75) in aqueous solutions stored in polyethylene tanks under shade or sunlight. Chemical analysis of aqueous solutions sampled at 0, 24, 48, 72, 168 and 336 h revealed that imidacloprid was relatively stable. Our results indicate that polyethylene tanks are adequate to protect imidacloprid from photo degradation.

Decapitation impacting effect of topically applied chlorpyrifos on acetylcholinesterase and general esterases in susceptible and resistant German cockroaches (Dictyoptera: Blattellidae).

The effect of topically applied chlorpyrifos on acetylcholinesterase and other esterases in heads and decapitated bodies of CSMA and Crawford German cockroaches was examined with spectrophotometric enzyme assay and native polyacrylamide gel electrophoresis. The toxicity of chlorpyrifos was greatly reduced in decapitated CSMA male cockroaches with LD50 value 17.1-fold higher than that of normal CSMA cockroaches. Acetylcholinesterase activity from heads was significantly higher in the Crawford compared with the CSMA strain and did not change until 24 h after chlorpyrifos in vivo treatment in both strains. The p-nitrophenyl butyrate (NPB) esterase activities from both heads and decapitated bodies of the resistant Crawford strain were significantly greater than the susceptible CSMA strain. The p-NPB esterase activity was significantly inhibited by chlorpyrifos in vivo treatment, and total p-NPB esterase activity was significantly reduced in decapitated bodies compared with heads of both strains. Native polyacrylamide gel electrophoresis (PAGE) analysis of extracts solubilized with Triton X-100 from heads and decapitated bodies revealed five major esterase bands and an acetylcholinesterase (AChE) band with a high capability of hydrolyzing alpha-naphthyl butyrate and acetylthiocholine, respectively. In the heads of susceptible CSMA male cockroaches, the activity of mobile isozymes d1 and d2 was completely inhibited at 24 h after chlorpyrifos application, and isozyme e was partially inhibited. In contrast, isozymes c1 and c2 from the decapitated bodies of CSMA cockroaches were mostly affected at 24 h after the topical application of chlorpyrifos. The activities of acetylcholinesterase and esterase isozymes a and b from the decapitated body remained uninhibited in both strains. Inhibition of isozymes d1 and d2 seems to be more important in chlorpyrifos intoxication than acetylcholinesterase.

In vivo study on combined toxicity of Metarhizium anisopliae (Deuteromycotina: Hyphomycetes) strain ESC-1 with sublethal doses of chlorpyrifos, propetamphos, and cyfluthrin against German cockroach (Dictyoptera: Blattellidae).

The effect of Metarhizium anisopliae (Metschnikoff) Sorokin strain ESC-1 alone and in combination with sublethal doses of commercial formulations of chlorpyrifos, propetamphos and cyfluthrin on mortality of CSMA strain of German cockroach, Blattella germanica (L.), was determined by conducting in vivo studies that included 3 bioassays. Spores of M. anisopliae cultured on SDAY media had germination of >90%. Based on bioassay 1, doses ranging from 0.5 to 300 ppm of chlorpyrifos and propetamphos, and 0.05 to 40 ppm of cyfluthrin were selected for bioassays 2 and 3. Cockroach mortality ranged from 5 to 20% for insecticides alone and 48 to 70% for insecticides + M. anisopliae in bioassay 2. In bioassay 3, mortality ranged from 15 to 60% for insecticides and 57.5 to 92.5% for insecticides + M. anisopliae. Percentage of cockroach mortality resulting from insecticide + M. anisopliae combinations was significantly higher than insecticide alone. Mortality was also significantly higher in certain insecticide + M. anisopliae combinations than M. anisopliae alone. There was no significant interaction between M. anisopliae and insecticides with their concentrations in bioassay 2, indicating an additive effect. But in bioassay 3, a significant interaction was observed when M. anisopliae was combined with multiple insecticide concentrations. The interaction indicated an additive effect for chlorpyrifos and cyfluthrin, and a synergistic effect for propetamphos. There were significant differences in LT50 among various treatment combinations. M. anisopliae alone or insecticide + M. anisopliae combinations did not affect body weight in treated German cockroaches.

Comparison of esterases between life stages and sexes of resistant and susceptible strains of German cockroach (Dictyoptera: Blattellidae).

Esterase activity between the resistant Crawford and susceptible CSMA strains of German cockroach, Blattella germanica (L.), was compared with the substrates alpha- and beta-naphthyl acetate across sex and nymphal age classes. Esterase isozyme analysis with native polyacrylamide gel electrophoresis also was conducted to identify quantitative and qualitative differences between strains, sexes, and age classes. The Crawford strain was highly resistant to cypermethrin, propoxur, and permethrin with a resistant ratio (RR) of 17.26, 15.75, and 13.53, respectively, and mildly resistant to chlorpyrifos (RR 5.62). The alpha-NA and beta-NA esterase activities in the Crawford strain were significantly higher than those activities in the CSMA strain in both nymphal and adult stages. In the Crawford strain, the enzyme activity in nymphs was significantly higher than that in adults, but such differences were not observed in the CSMA strain. The mobile isozymes a and c stained more intensely than others in every developmental stage and sex of both strains but showed greater intensity in the Crawford strain. Another intensely stained isozyme b was observed only in the homogenates from the Crawford strain. The combination of isozyme b and the overproduced isozyme a and c in the Crawford strain seems to be responsible for the difference in total esterase activity between the CSMA and Crawford strains.

Purification and characterization of an esterase isozyme from insecticide resistant and susceptible strains of German cockroach, Blattella germanica (L.).

The most active forms of esterases (E5, E6 and E7) from the German cockroach, Blattella germanica (L.) were purified from resistant and susceptible strains. About 45-155 fold purification with a 11-16% of total esterase recovery was achieved after different column chromatography and preparative gel electrophoresis. Elution profiles of resistant and susceptible strains were similar, but esterase E6 activity was higher in the resistant strains. Kinetic analyses indicate no differences in Km values between the resistant and susceptible strains. However Vmax was significantly higher in resistant strains. Inhibition of esterase activity by paraoxon, chlorpyrifos and propoxur did not suggest any structural differences in esterase E6 between strains. From these results we suggest that insecticide resistance in German cockroach is due to the increased production of E6 esterase. The role of E6 may be sequestration of toxic molecules rather than hydrolysis.

Subcellular distribution and characterization of esterase isozymes from insecticide-resistant and -susceptible strains of German cockroach (Dictyoptera: Blattellidae).

Esterases from insecticide-resistant and -susceptible strains of German cockroach, Blattella germanica (L.), were isolated and analyzed for differences in activity. The isozymes E5, E6, E7, and E8 of resistant strains indicated about two- to fivefold increases in activity compared with those of the susceptible strain. These isozymes constituted approximately 60% of the total activity in the resistant strains, whereas they contributed only about 40% activity in the susceptible strain. Subcellular distribution studies showed that most esterase activity is present in the 100,000 x g fraction of the homogenate (cytosolic). Only a small portion of activity was membrane bound. Molecular weights of the esterase isozymes calculated based on their retardation coefficients ranged between 48 and 81 kd.

Activity and electrophoretic characterization of esterases in insecticide-resistant and susceptible strains of German cockroach (Dictyoptera: Blattellidae).

Strains of German cockroach, Blattella germanica (L.) were tested for resistance to three insecticides using the time-mortality response technique in comparison with known susceptible strains. Dursban-R and Macy strains indicated high levels of resistance to chlorpyrifos and moderate resistance to propoxur and cypermethrin. The hydrolytic activity of esterase enzymes was determined with a model substrate, p-nitrophenyl acetate. The specific activity of the enzymes increased with a corresponding increase in substrate concentration. Maximum activity was observed at 80 microM. The resistant strains had significantly higher activity than the susceptible strains. The enzyme activity also increased with an increase in pH. Highest esterase activity was observed at pH 8.0 for all the strains. The calculated Michaelis Menten constant (Km) values for the resistant strains were nearly two-fold higher than for the susceptible strains. Nondenaturing gel electrophoresis revealed differences in isozyme composition. In total, 10 esterase bands were detected, and these bands were characterized using different inhibitors and substrates.

Field worker exposure to selected insecticides applied to corn via center-pivot irrigation.

Field workers were monitored for dermal and respiratory exposure to chlorpyrifos (with and without crop oil), carbaryl, and permethrin at reentry intervals of 2, 4, 8, 24, and 48 h after application. Insecticides were applied to R3 stage corn through an overhead center-pivot irrigation system. Dermal exposure was measured by analyzing 18 gauze pads attached to the clothing of workers to represent human body regions. Hand exposure was determined using cotton gloves. Respiratory exposure was determined using portable air samplers equipped with polyurethane foam plugs to trap ambient insecticide residues. Gas liquid chromatography was used to quantify residues of chlorpyrifos and permethrin in gauze pads, gloves, and foam plugs. Carbaryl residues in pads, gloves, and foam plugs were analyzed using high-performance liquid chromatography. Highest dermal and respiratory exposures were found at the 2-h reentry interval. Exposures decreased as reentry interval increased. Dermal exposure was primarily confined to the hands. Residues detected by air samplers ranged from 0 to 0.03 micrograms/liter. Based on the estimated percentages of acute toxic dose (all less than 0.00038%), the risk of acute toxicity to workers at the intervals studied was low.

Exposure of applicators and residents to chlordane and heptachlor when used for subterranean termite control.

Research was conducted to assess dermal and respiratory exposure to applicators from chlordane and heptachlor used for subterranean termite control and exposure to residents of treated homes. Dermal exposure of 29 applicators was evaluated by using gauze pads attached to outer and inner clothing at selected body regions. Respiratory exposure of applicators was monitored with personnel-type air samplers worn during application periods. Air samplers were equipped with polyurethane foam plugs to trap airborne chlordane and heptachlor. Exposure of residents was measured by sampling ambient air of 19 homes treated with the termiticides. Electric air samplers equipped with foam plugs were used to monitor ambient air from the basement, the kitchen, and one bedroom at: 24 h prior to termiticide application, during application, and post-application at 24 h, 1 wk, and monthly for 6 mo. Applicator dermal exposure was estimated based on exposure rates to each body region. Respiratory exposure was estimated based on termiticide concentrations in the air and on the ventilation rate of a person doing light work. Residents' exposure was estimated based on the amount of termiticide present in ambient air. Results indicated that applicator exposure rates to chlordane and heptachlor were 2.54 and 1.88 micrograms/kg/h, respectively. Residents were exposed to less than 0.69 and 2.86 micrograms/m3 of chlordane and heptachlor, respectively. During this research, the application of termiticide containing chlordane and heptachlor posed minimal risk in terms of acute exposure to either the applicators or the residents of the treated homes.