Shripat T. Kamble

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.

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)

Abstract 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.

Bioavailability of Chlorantraniliprole and Indoxacarb to Eastern Subterranean Termites (Isoptera: Rhinotermitidae) in Various Soils

ARSTRACT A laboratory study was conducted to determine the toxicity of indoxacarb and chlorantraniliprole to Eastern subterranean termites, Reticulitermes flavipes (Kollar) (Isoptera: Rhinotermitidae) resulting from topical applications and exposure to treated soil. Soils with varying organic matter (0.57–3.64%) and chemical characteristics were used in termiticide bioassays. Lethal dose resulting from topical application indicated that chlorantraniliprole was two- to 11-fold more toxic than indoxacarb. Lethal concentration assays yielded opposite results where concentrations of indoxacarb in soil that caused either 50 or 90% mortality of R. flavipes workers at 48 and 144 h were two- to six-fold lower than chlorantraniliprole. The bioavailability of indoxacarb and chlorantraniliprole was negatively correlated with soil organic matter. Our results suggest that indoxacarb is more bioavailable to termites in soil than chlorantraniliprole based on calculated bioavailability ratios. However, how these laboratory results correlate to actual field application data and termite efficacy is unknown, and more research is needed. These compounds seem to have excellent activity on termites and have potential to provide new modes of action and new chemistry as liquid termiticides.

Concentration-Dependent Degradation of Three Termiticides in Soil Under Laboratory Conditions and Their Bioavailability to Eastern Subterranean Termites (Isoptera: Rhinotermitidae)

Abstract Degradation and bioavailability of imidacloprid, fipronil, and bifenthrin applied at label rates ([AI], wt:wt in soil) in the loamy soil of Nebraska were determined over a 6-mo duration. Based on the calculated half-lives of the three termiticides, it was concluded that the degradation rate was lowest when a termiticide was applied at the highest label rate. Bioassays of Reticulitermes flavipes (Kollar) (Isoptera: Rhinotermitidae) conducted at 8, 31, 65, 90, 135, 160, and 180 d posttreatment showed an inverse relationship between the LT90 values and the variable concentrations. At day 180, exposures to all the termiticide-treated soil samples (concentration × termiticide) resulted in 100% mortality of R. flavipes workers. However, lower LT90 values were observed for termites exposed to soils treated with highest label rates even when the treated soils were aged in the lab for 6 mo. This suggested a higher bioavailability of these three termiticides when applied at higher application rates. Termite mortality was fastest for bifenthrin followed by fipronil and imidacloprid.

Comparison of Bt (Bacillus thuringiensis Berliner) maize and conventional measures for control of the European corn borer (Lepidoptera: Crambidae).

Field experiments were conducted in 1997 to compare the efficacy Bt (Bacillus thuringiensis Berliner) maize hybrids and two conventional measures for control of the European corn borer, Ostrinia nubilalis (Hubner). Treatments consisted of transgenic Bt maize hybrids and their non-Bt isolines, and isolines treated with a formulated Bt or permethrin insecticide. All control measures significantly reduced O. nubilalis damage in terms of tunnels per plant, length of tunneling, and larvae per plant. The following hierarchy in terms of O. nubilalis efficacy was observed: transgenic Bt > permethrin > formulated Bt > control. In most cases, transgenic Bt maize was most effective in preventing European corn borer damage to ear shanks and generally produced the highest grain yields.

Effects of Decreasing Thermophotoperiod on the Eastern Subterranean Termite (Isoptera: Rhinotermitidae)

Abstract Eastern subterranean termite, Reticulitermes flavipes (Kollar), workers were exposed to decreasing temperatures and a shift in photoperiod to simulate conditions that are encountered during the fall in eastern Nebraska. Mean water and fat content in termites exposed to a decreasing thermophotoperiod did not differ significantly from controls or laboratory colony termites. Survival was higher for termites subjected to a decreasing thermophotoperiod than for controls. This could be attributed to acclimation to low temperatures or a delayed mortality due to lowered metabolic activity at low temperature. Previously reported data on soil temperatures taken in Lincoln, NE, at a depth of 91.4 cm showed that the temperature rarely went below 0°C. Our results, observations from previous reports of R. flavipes found at depths >100 cm during the winter, and previously determined lower lethal temperatures and supercooling points suggest that successfully overwintering R. flavipes colonies retreat to soil depths where freezing temperatures are not encountered.

Influence of Temperature on Rate of Uptake and Subsequent Horizontal Transfer of [14C]Fipronil by Eastern Subterranean Termites (Isoptera: Rhinotermitidae)

Abstract The effect of temperature on [14C]fipronil uptake and transfer from donor (D) to recipient (R) Reticulitermes flavipes (Kollar) (Isoptera: Rhinotermitidae) workers was evaluated. Test chambers used in the fipronil uptake study were constructed from petri dishes containing autoclaved soil treated with 1 ppm [14C]fipronil (1.14 μCi of total radioactivity per petri dish), distilled water, and R. flavipes workers. Test chambers were held in environmental growth chambers preset at 12, 17, 22, 27, and 32°C. For the fipronil transfer study, donor termites stained with Nile blue-A were exposed to soil treated with 1 ppm [14C]fipronil for 2 h. Donors were then combined with unexposed recipient termite workers at either 1D:5R, 1D:10R, or 1D:20R ratios. Test chambers consisted of a nest and feeding chamber connected by a piece of polyethylene tube and held in growth chambers at 12, 17, 22, 27, and 32°C. Worker termites were sampled over time and the amount of [14C]fipronil present was measured by scintillation counting. Some degree of uptake and transfer occurred at all temperatures and ratios in this study. The highest level of uptake occurred by termites held at 22–32°C, followed decreasingly by 17 and 12°C. Maximum transfer of [14C]fipronil occurred at the higher ratios (1:5 > 1:10 > 1:20) of donors to recipients. Data presented in this study suggest that temperature is one of the key factors affecting the rate of uptake and subsequent horizontal transfer of [14C]fipronil in subterranean termites.

Biochemical characterization and purification of esterases from three strains of German cockroach, Blattella germanica (Dictyoptera: Blattellidae)

Three strains of German cockroach, Blattella germanica (L.) showed varying levels of resistance to chlorpyrifos, methyl parathion, propoxur, bendiocarb, and cypermethrin. The general esterase activity was at least twofold higher than susceptible strain. The subcellular distribution studies revealed that the majority of the esterase activity is present in the 100,000g cytosolic fraction. Only a small portion of the activity was membrane bound. Using non-denaturing gel electrophoresis, ten isozymes were identified in German cockroaches. These isozymes were isolated individually from the gels and analyzed for differences in activity. The isozymes E5, E6, and E7 of resistant strains had significantly higher specific activities when compared with the susceptible strain. The purification process using various column chromatography and preparative gel electrophoresis resulted in 9–11% of total esterase recovery. About double the amount of E6 was recovered from the resistant strains when compared with the susceptible strain. Kinetic analyses of E6 did not indicate differences in Km and Vmax values between the resistant and susceptible strains. Also, inhibition of esterase activity by paraoxon, chlorpyrifos, and propoxur did not suggest any structural differences in esterase E6 between strains. The results suggest that the increased production of E6 esterase contributes to insecticide resistance in German cockroaches. The role of E6 may be sequestration of toxic molecules rather than hydrolysis.

Distribution of sub-slab injected dursban® TC (chlorpyrifos) in a loamy sand soil when used for subterranean termite control

Creation of continuous soil insecticide barriers is a common method of protecting existing structure from subterranean termite infestations. Previously registered termiticides (aldrin, benzene hexachloride, chlordane, dieldrin and heptachlor) have provided insecticidal activity in the soil for more than 20 years (Johnston et al. 1971; Mauldin et al. 1987). Due to human health and environmental concerns, the U.S. Environmental Protection Agency has canceled these termiticides. Of the currently registered active ingredients (AI) labeled for controlling subterranean termites, chlorpyrifos (Dursban | TC) has been the most widely used by commercial pest control operators (PCOs) (Mix 1988).

Temporal changes in chlorantraniliprole and indoxacarb in four midwestern soils and bioefficacy against the eastern subterranean termite (Isoptera: Rhinotermitidae).

ABSTRACT Temporal changes in indoxacarb and chlorantraniliprole were determined in four midwestern soils by simulating commercial field applications of termiticides. Indoxacarb (0.0625 and 0.125%) and chlorantraniliprole (0.05 and 0.10%) were applied to each soil type in a rotating cement mixer to ensure uniform distribution of active ingredient (AI). Temporal and spatial changes in termiticide concentrations were determined by sampling soil cores subdivided at different depths (0–20, 20–40, and 40–61 cm) at various intervals up to 705 d after application. Percentage loss of indoxacarb was initially greater (0–180 d) than losses after 180 d. The lowest indoxacarb extractable concentrations were detected in soils closest to the surface. Chlorantraniliprole losses with time from all soils were slower than indoxacarb, with no differences observed with soil type or depth. Bioefficacy was evaluated in laboratory glass tube bioassays that monitored the distance of termite penetration into treated soils and resulting eastern subterranean termite, Reticulitermes flavipes (Kollar) (Isoptera: Rhinotermitidae), worker mortality. Bioassay data revealed that R. flavipes termites were unable to completely penetrate 50 mm of indoxacarb- and chlorantraniliprole-treated soils at 0 d after treatment; however, termites were not deterred from foraging in these soils indicating no repellency to these termiticides. Termites completely penetrated (50 mm) soils treated with indoxacarb (0.0625%) by 360 d and complete penetration occurred in all soils treated with indoxacarb (0.0625 and 0.125%) by 705 d. Termites were unable to completely penetrate chlorantraniliprole-treated soils at 705 d. Mortality of termite workers was high in all chlorantraniliprole-treated soils at all sampling intervals. These data confirm that vertical differences in termiticide persistence occur in various soils.