Laboratory Evaluation of the Novel Naturally Derived Compound Spinosad against Ceratitiscapitata

Laboratory studies were conducted to determine the effect of the naturally derived compound spinosad on Ceratitis capitata Wied. (Diptera, Tephritidae). The organophosphate fenthion was used as a standard. Direct dose-dependent mortality and reduced fecundity were observed in oral treatment of adults with spinosad. The LC₉₀ values 14 h and seven days after treatment were 19·50 and 0·49 mg litre⁻¹ respectively. Fenthion was less active (the LC₅₀ eight days after treatment was 1·17 mg litre⁻¹) and did not affect the fecundity of the fly. Adults were also very susceptible to spinosad and fenthion via residual contact. For spinosad, 100% mortality was recorded 48 h after treatment for a dose of 10 mg litre⁻¹. Spinosad was more effective than fenthion in suppressing larval development when neonate larvae were reared on treated diet supplemented with a range of concentrations from 0·02 to 0·83 mg kg⁻¹ diet. Last-instar larvae were much less susceptible to spinosad or fenthion when exposed via dipping or when they pupated in treated medium and both products had similar performance. A lack of ovicidal activity was observed in direct egg-treatments with spinosad but significant reductions from 1 mg litre⁻¹ onwards were recorded for fenthion.     

Effect of Hydrogen Cyanide and Carbonyl Sulphide on the Germination and Plumule Vigour of Wheat

Several factors which may influence the germination of wheat fumigated with hydrogen cyanide or carbonyl sulphide were investigated. Dosages of hydrogen cyanide ranged from 10 mg litre⁻¹ for 24-h exposure up to 150 mg litre⁻¹ for 96-h exposure. Dosages of carbonyl sulphide ranged from 25 mg litre⁻¹ for 24-h exposure up to 500 mg litre⁻¹ for 72-h exposure. The experiments were conducted on wheat of 11·4, 13·8 and 15·7% moisture content. The higher levels of these fumigants exceed those needed for control of insects in wheat. Germination was not diminished and may have been slightly enhanced with hydrogen cyanide, but was diminished by high levels of carbonyl sulphide in the drier wheat. The plumule length was reduced following all dosages of hydrogen cyanide, but only after high dosages of carbonyl sulphide, especially on the driest wheat. It is concluded that hydrogen cyanide and carbonyl sulphide could be used to control insects in wheat without affecting seed viability, provided that concentrations are carefully controlled.     

Fumigant Toxicity of Citruspeel Oils against Adult and Immature Stages of Storage Insect Pests

The biological action of citruspeel oils was shown to depend on a strong fumigant action. Bioassays conducted in air-tight glass chambers showed that all the six citrus oils tested had vapour toxicity towards adults of Callosobruchus maculatus F., Sitophilus zeamais Motsch. and Dermestes maculatus Deg. The 24-h LC₅₀ value of limepeel oil (a typical citrus oil) vapour against C. Maculatus was 7·99 μl litre⁻¹ which made it 1·5 and 1·6 times less toxic against the smaller S. zeamais and the larger D. maculatus adult insects. When immature stages were fumigated, limepeel oil vapour had 24-h LC₅₀ values of 7·8 and 21·5 μl litre⁻¹ against eggs of C. maculatus and D. maculatus respectively, and 9·1, 17·8 and 23·1, 23·9 μl litre⁻¹ against early larvae, pupae of C. maculatus and late larvae, pupae of D. maculatus respectively. X-ray studies showed that fumigated C. maculatus larvae within cowpea grains died immediately without further development. The bioactivities of five other citruspeel oils were similar to that of limepeel oil. Bioassays showed that sorption of citruspeel oil fumes occurred in the presence of grains or strips of dried fish, and that this tended to reduce the amount available for fumigant action outside the materials. The problems presented by sorption may hinder the development of citrus oils into practical fumigants for large-scale treatments of stored commodities.     

Synthesis and Structure–Activity Relationships for the Fungicidal Activity of O,O-bisaryl sec-butylphosphonates

Sixteen O,O-bisaryl sec-butylphosphonates have been synthesised by condensing sec-butylphosphonyl dichloride with substituted phenols. The compounds were tested against two phytopathogenic fungi, Rhizoctonia bataticola and Helminthosporium oryzae. The most active compound against R. bataticola is O,O-bis(3-methylphenyl) sec-butylphosphonate (ED₅₀ 29·56 mg litre^-1) and against H. oryzae, O,O-bis(2-chlorophenyl) sec-butylphosphonate and its para-chloro analogue (ED₅₀ 0·14 and 0·13 mg litre^-1 respectively). Quantitative structure–activity relationships on the fungicidal activity have been analysed by means of multiple regression analysis using physicochemical substituent parameters. Electronic parameters viz., σ and F have expressed significant variability in fungitoxicity against both the fungi, viz. R. bataticola and H. oryzae. Hydrophobic and steric parameters are also found to be important in the correlation studies. © 1997 SCI.     

Trichoderma species associated with green mould disease of Pleurotus ostreatus and their sensitivity to prochloraz

Green mould disease causes serious economic losses in Pleurotus ostreatus crops worldwide, including in Italy, where prochloraz is the only chemical fungicide allowed to control the disease. The effectiveness of the doses 0.01, 0.05, 0.25 and 1.25 μL L⁻¹ (field dose) of prochloraz (Sponix Flow, 450 g L⁻¹), against colony growth rate and spore germination of Trichoderma pleuroti, T. pleuroticola and T. guizhouense strains on wheat straw extract agar plates were evaluated. Complete inhibition of Trichoderma pleuroti and T. pleuroticola growth was shown by the field dose of prochloraz, and also by the 0.25 μL L⁻¹ dose for T. pleuroti. Complete inhibition of spore germination occurred for all Trichoderma strains at field dose, and at 0.25 μL L⁻¹ for T. pleuroti strains. In in vivo assays, the effect of prochloraz doses 0.05, 0.25 and 1.25 μL L⁻¹ on colonization of straw substrate by T. pleuroti, T. pleuroticola and T. guizhouense inoculated at two spore densities (10² and 10⁵ spores mL⁻¹) immediately after P. ostreatus spawn was studied. Trichoderma pleuroti and T. pleuroticola were both responsible for green mould disease, whereas T. guizhouense was not pathogenic. Trichoderma pleuroti was more aggressive than T. pleuroticola. Prochloraz was effective against T. pleuroti at the field dose, and against T. pleuroticola at 0.25 and 1.25 μL L⁻¹. The study on Trichoderma × Pleurotus interaction type showed that Trichoderma species were active against the mycelial growth of P. ostreatus by competition for space and nutrients, and neither hyphal interaction nor effect by volatile or nonvolatile metabolites occurred.     

Laboratory studies with antifeedants against larvae of Boarmia (Ascotis) selenaria on alfalfa

The antifeedant effect of five organotin compounds (fentin acetate, fentin hydroxide, fentin chloride, cyhexatin and fenbutatin oxide) and of three other compounds known to possess antifeeding activity (guazatine triacetate, 4′-chloroacetophenone isobutyrylhydrazone and thiram) was investigated by feeding treated alfalfa to larvae of Boarmia selenaria. The three fentins and cyhexatin were highly active at 0.1 g litre^?1, the order of activity at this concentration being fentin chloride > fentin hydroxide > fentin acetate ? cyhexatin, whereas the other compounds were practically inactive at either this or a somewhat higher concentration (0.5 g litre^?1). Guazatine triacetate had a concentration-independent antifeedant effect at much higher concentrations (5–20 g litre^?1).     

Synthesis and Evaluation of New Ethyl 2,3- Dihydro-3-oxoisothiazolo[5,4-b]pyridine- 2-alkanoate Derivatives as Potential Herbicides

Several ethyl 2,3-dihydro-3-oxoisothiazolo[5,4-b]pyridine-2-alkanoate derivatives were synthesized as herbicides. Only 5-methyl derivatives inhibited both hypocotyl and root growth in the lettuce (Lactuca sativa L.) seedling test at 100 mg litre^-1. Only ethyl propionate and valerate derivatives showed significant inhibition at 0·1 mg litre^-1, whereas ethyl acetate or butyrate derivatives were inactive. Contrary to unoxidized derivatives, the inhibitory effect of 1-oxide and 1,1-dioxide derivatives was strongly dependent on concentration; ethyl 2,3-dihydro-5-methyl-3-oxoisothiazolo[5,4-b]pyridine-2-propionate 1,1-dioxide inhibited 100% of germination at 100 mg litre^-1 and 45% of lettuce seedling growth at 0·1 mg litre^-1. Quantitative structure–inhibition of growth relationship analysis carried out by adaptive least-squares (ALS) method gave a good correlation with small and hydrophobic 5-substituents as well as with odd carbon-chain ethyl alkanoates in position 2. Active compounds did not show auxin-like activity from 0·1 to 100 mg litre^-1. © 1997 SCI.     

The algaecidal activity of some substituted 1,3-diphenylureas, 1-phenyl-3-(2-pyridyl)ureas and the corresponding thioureas

Twelve ureas and thioureas with 1,3-diphenyl- and 1-phenyl-3-(2-pyridyl) were tested as potential herbicides in a simple screen against two species of algae Chlorella fusca and Anabaena variabilis. Several were shown to inhibit growth at 100 mg litre^?1 but only 1-[2,4-bis(azidosulphonyl)phenyl]-3-(2-pyridyl)urea and 1,3-bis(4-isopropyl- idenehydrazinosulphonylphenyl)thiourea showed any activity at 1 mg litre^?1. This compares with the well-established urea herbicide diuron which, in identical tests, gives similar inhibition of growth at concentrations as low as 0.01 mg litre^?1.     

Inhibition of sterol biosynthesis in cell-free extracts of Botrytis cinerea by prochloraz and prochloraz analogues

The sensitivity of cytochrome-P450-dependent sterol 14α-demethylase (P450_14DM) to prochloraz and several prochloraz analogues was studied in a cell-free assay of Botrytis cinerea Pers. ex Fr. The EC₅₀ values (concentrations which inhibited radial growth of B. cinerea by 50%) of the compounds tested ranged from 3.3 × 10 ?8 to 1.7 × 10 ?5 M. The IV₅₀ values (concentrations which inhibited cell-free C₄-demethyl sterol synthesis by 50%) in cell-free assays of B. cinerea ranged from 2.6 × 10 ?9 to 4.4 × 10 ?7 M. Ranking compounds in terms of their relative inhibitory potencies showed quite similar trends to the order of fungitoxicity, but the IC₅₀ values did not quantitatively reflect the differences in toxicity. Therefore, the differential inhibition of cell-free P450_14DM activity by these compounds cannot fully account for their differences in activity towards B. cinerea. Additional mechanisms must be involved. The compounds tested were generally more potent in the B. cinerea assay than in similar assays developed for Penicillium italicum Wehmer and, in particular, Saccharomyces cerevisiae Meyen. This correlated with the relatively higher activity of most test compounds to B. cinerea. Results suggest that the cell-free assay of B. cinerea is more useful to evaluate candidate fungicides as inhibitors of sterol 14α-demethyiase activity than similar assays from model organisms. The present study confirms that the affinity of prochloraz analogues for P450_14DM depends on the nature of the N-1 substituent of the imidazole and the azole ring. It was also found that addition of an amino group at C-2 of the imidazole moiety of prochloraz gave a compound (6) which inhibited 4, 4-demethyl sterol biosynthesis in B. cinerea at a different site from the P450_14DM. This was confirmed by the observation that laboratory-generated triadimenol-resistant isolates of B. cinerea showed reduced sensitivity to triadimenol and prochloraz, but not to compound 6.     

The response of pyriproxyfen-resistant and susceptible Bemisia tabaci Genn (Homoptera: Aleyrodidae) to pyriproxyfen and fenoxycarb alone and in combination with piperonyl butoxide

Pyriproxyfen was effective against susceptible Bemisia tabaci eggs at a LC₅₀ of 0.003 mg litre⁻¹ and against nymphs at 0.02 mg litre⁻¹. In comparison, eggs of a laboratory selected, pyriproxyfen-resistant B tabaci strain, originating in an Israeli greenhouse, exhibited 6500-fold resistance and nymphs exhibited 1100-fold resistance. Eggs and nymphs of a strain from an Israeli sunflower field exhibited 450 and 210-fold resistance in comparison to the susceptible standard. Fenoxycarb was generally less effective than pyriproxyfen against B tabaci eggs and nymphs but was unaffected by pyriproxyfen resistance. Piperonyl butoxide (PB) was antagonistic to pyriproxyfen, and this increased with increasing pyriproxyfen resistance. PB had no effect on the toxicity of fenoxycarb. Collectively, these data imply that the modes of action of pyriproxyfen and fenoxycarb are distinct, despite the structural similarities of these molecules. Possible reasons for the antagonism of PB against pyriproxyfen are discussed. © 1999 Society of Chemical Industry     

In-vivo effects of 2,4-D and atrazine on cytochrome P-450 and insecticide toxicity in southern armyworm (Spodoptera eridania) larvae

After feeding 2,4-D or atrazine in a diet to southern armyworm (Spodoptera eridania Cram.) larvae for three days, the effect on total content and activities of cytochrome P450 and on insecticide toxicity were determined. Both 2,4-D and atrazine induced cytochrome P450-catalyzed aldrin epoxidation (AE) and methoxyresorufin O-demethylatin (MROD). The 2,4-D was a more potent inducer for total cytochrome P450 content, whereas atrazine disproportionately increased AE. Both compounds increased MROD significantly. The apparent kinetic characteristics of AE indicates that 2,4-D and atrazine induced similar P450 isozymes (K_m 8.78 and 7.80 μM, respectively), which may differ from the constitutive isozyme (K_m 3.14 μM). The 2,4-D-induced cytochrome P450 contributed to decreased carbaryl and permethrin toxicity, whereas the atrazine-induced cytochrome P450 caused decreased parathion and permethrin toxicity. The carbaryl toxicity correlated directly with 2,4-D-induced total P450 content and activities but not with atrazine-induced changes. The 2,4-D and atrazine also induced nonspecific esterase activity which may contribute to permethrin detoxification.     

Sensitivity of European Plasmopara viticola populations to cymoxanil

Between 1995 and 1997, 278 grape downy mildew (Plasmopara viticola) populations originating from European vineyards were characterised for their sensitivity to cymoxanil in a leaf-disc assay. The sensitivity profile revealed a wide distribution, with minimum inhibitory concentrations (MIC) ranging from 10 to more than 800 mg litre⁻¹. EC₅₀ values ranged from 1 to more than 800 mg litre⁻¹ with an average of 125 mg litre⁻¹. The sensitivity distribution was stable between 1995 and 1997. Surprisingly, populations from Portugal appeared significantly more sensitive than those from France or Italy, which could not be linked to differential cymoxanil usage in these countries. P viticola populations collected outside Europe and never exposed to cymoxanil appeared significantly more sensitive than exposed European populations, with an average EC₅₀ value of 10 mg litre⁻¹. The level of sensitivity of European P viticola populations was relatively unaffected by the number of cymoxanil applications made during a season or by the number of years of cymoxanil use. No link was found between the level of sensitivity in the leaf-disc assay and the level of performance of the cymoxanil mixtures used in the fields where the populations originated. Specific field trials conducted in Italy and Portugal have shown that the performance of cymoxanil-based mixtures remained good even on populations of the grape downy mildew fungus characterised as less sensitive in the leaf-disc assay. While there are no baseline sensitivity data for pre-commercialisation P viticola populations, the results of our study suggest that a shift in sensitivity (12.5-fold) may have occurred in some areas since introduction of cymoxanil on grapes nearly 20 years ago. Because cymoxanil is never used alone, it is difficult to determine whether or not practical resistance is occurring in European vineyards. © 1999 Society of Chemical Industry     

In-vivo evaluation of adjuvants for more effective control of celery leaf-spot (Septoria apiicola) and powdery mildew (Erysiphe graminis) of wheat with fungicides

The effects of seven adjuvants (at 0, 0.5, 1.0 and 2.0 g litre^?1) on the efficacies of four fungicides al 0.5 g litre^?1 were studied in the laboratory for the control of leaf-spot in celery (caused by Septoria apiicola) and powdery mildew on winter wheat (caused by Erysiphe graminis). The most effective fungicides for controlling leaf-spot were: tebuconazole + triadimenol = flutriafol > mancozeb + oxadixyl > prochloraz. However, addition of adjuvant to the fungicides gave a modified pattern of effectiveness. The efficacy of flutriafol was strongly enhanced by addition of all adjuvants, but those of prochloraz and mancozeb+oxadixyl only partially so. The tested adjuvants were mineral oil + surfactant, a polymer/alkoxylated alkyl ether blend, an ethoxylated alkylphenol, an ethoxylated hexitan ester blend, an ethoxylated nonylphenol and an alkylpolysaccharide- based adjuvant mixture. However, the addition of adjuvants to tebuconazole + triadimenol had a negative effect. Of all the adjuvants tested, the nonylphenol ethoxylate and a mixture of mineral oil /surfactant and alkylpolysaccharides gave the highest efficacy with the fungicides, while the mineral oil/surfactant and the alkylpolysaccharides alone were less effective. There was a positive relationship between high concentrations of adjuvants and their effectiveness, but there were some exceptions. The most effective fungicides for control of powdery mildew in wheat were prochloraz, mancozeb + oxadixyl and tebuconazole + triadimenol. There was a linear relationship between the high efficacy of the fungicide and the concentration of adjuvants to control powdery mildew in wheat. The highest concentration of adjuvant (2-0 g litre^?1) gave the highest efficacy for the fungicides.     

Communication to the Editor Protection of Wood against the House Longhorn Beetle Hylotrupes bajulus with Sodium Chloride and Potassium Chloride

The effectiveness of aqueous solutions of sodium chloride and potassium chloride as wood preservatives was tested against larvae of the house longhorn beetle Hylotrupes bajulus (L.). Immersion of pine (Pinus sylvestris L.) blocks for 24 h provided only a shallow protective layer. In a test series according to EN 46 a concentration of 200 g litre^-1 potassium chloride was required for complete larval mortality within 12 weeks; 200 g litre^-1 sodium chloride failed to achieve this. With vacuum impregnation in tests according to EN 47 a concentration of 100 g litre^-1 sodium chloride achieved complete mortality of larvae within four weeks. Vacuum impregnation of 100 g litre^-1 potassium chloride attained complete mortality only after 12 weeks. Ovipositing female beetles did not avoid wooden blocks treated with either salt. © 1997 SCI.     

In-vitro and in-vivo nematicidal activities of the cyclic dodecapeptide omphalotin A

Omphalotin A, a cyclic dodecapeptide produced by submerged cultures of the basidiomycete Omphalotus olearius, exhibited in-vitro and in-vivo nematicidal activity. Meloidogyne incognita was the most sensitive nematode. At 2.0 mg litre⁻¹, 50% of the nematodes were dead after one hour. Heterodera schachtii, Radopholus similis and Pratylenchus penetrans were affected at higher concentrations. Incorporated into agar, the compound prevented infection of cucumber seedlings by M. incognita at concentrations of 1 mg litre⁻¹ and higher. In glasshouse tests, complete protection of cucumbers and lettuce was achieved between 2.5 and 10 mg litre⁻¹. No insecticidal activity was observed when Plutella xylostella, Phaedon cochleariae or Spodoptera frugiperda were fed material containing 4 g kg⁻¹ of omphalotin A. © 1999 Society of Chemical Industry     

Effect of ABT on the activity and rate of degradation of isoproturon in susceptible and resistant biotypes of Phalaris minor and in wheat

The effect of the monooxygenase inhibitor, 1-aminobenzotriazole (ABT) on isoproturon phytotoxicity and metabolism was studied in resistant (R) and susceptible (S) biotypes of Phalaris minor and in wheat (Triticum aestivum). Addition of ABT (2·5, 5 and 10 mg litre^-1) to isoproturon (0·25, 0·5, 1, 2 and 4 mg litre^-1) in the nutrient solution significantly enhanced the phytotoxicity of isoproturon against the R biotype. Isoproturon at 0·25 mg litre^-1 reduced the dry weight (DW) of the S biotype by 77%, whereas the R biotype required 4·0 mg litre^-1 for similar reduction. Addition of 10 mg litre^-1 of ABT to the 0·25 mg litre^-1 isoproturon caused 71 and 82% reduction in DW of R and S biotypes, respectively. Wheat was more sensitive to the mixture of isoproturon and ABT than the R biotype of P. minor. Reduced concentrations of ABT in the mixture from 10 to 2·5 mg litre^-1 increased the DW of the R biotype more than that of the S biotype. The R biotype metabolised [¹⁴C]isoproturon at a faster rate than the S biotype. ABT (5 mg litre^-1) inhibited the degradation of [¹⁴C]isoproturon in both biotypes of P. minor and in wheat. In the presence of ABT, about half of the applied [¹⁴C]isoproturon remained as parent herbicide in all the three species after two days. The metabolites were similar in the R and S biotypes and wheat as determined by co-chromatography with reference standards and mass spectroscopy (MS). ABT inhibited the appearance of the hydroxy and monomethyl metabolites and their conjugates in all the test plants. These results suggest that the activity of the enzymes responsible for the degradation of isoproturon is greater in the R than in the S biotype of P. minor, resulting in its rapid detoxification. Incorporation of the monooxygenase inhibitor ABT into the nutrient solution greatly inhibited the degradation of [¹⁴C]isoproturon in the R biotype and increased its phytotoxicity. Both hydroxylation and N-dealkylation reactions were found to be sensitive to ABT; inhibition of hydroxylation was greater than that of demethylation. Since ABT could not completely suppress isoproturon degradation, it is possible that more than one monooxygenase is involved. © 1998 SCI     

Effect of fipronil seed treatments on the germination and early growth of rice

Fipronil seed treatments were evaluated to determine whether they directly influence germination and subsequent seedling growth in rice (Oryza sativa L). Continuous seed exposure to fipronil (four days) at 2 000 mg litre⁻¹ significantly impaired germination (P < 0.001). When exposure was restricted to a 1-h period 48 h after the initiation of germination, early post-germination growth was also impaired (assessment two days after exposure, P < 0.05). The proportion of seeds satisfying our criteria for normal germination fell by 2.3 and 2.6% respectively across 17 cultivars. Cultivar effects were highly significant (P < 0.001). When exposure to fipronil (2 000 mg litre⁻¹) was restricted to 2 h at initial seed wetting no significant growth impairment occurred. No significant differences (P > 0.05) were found between shoot lengths or root system dry weights of control plants and plants developing from seed exposed continuously (two days) to fipronil at rates of up to 2 000 mg litre⁻¹ during germination and harvested nine days after sowing. Treating germinated seed with fipronil for 1 h immediately prior to sowing at rates of up to 4 000 mg litre⁻¹ did not result in significant changes (P < 0.05) in plant growth parameters at either nine or 25 days after sowing. No evidence of fipronil having a direct phytostimulatory effect on rice was obtained. © 1999 Society of Chemical Industry     

Pesticidal properties of parthenin (from Parthenium hysterophorus) and related compounds

Eleven sesquiterpene lactone derivatives of parthenin ( 1 ), obtained from wild feverfew, Parthenium hysterophorus, were prepared by chemical and photochemical transformations. The compounds tested were a pyrazoline adduct ( 2 ) of parthenin, its cyclopropyl ( 3 ) and propenyl ( 4 ) derivatives, anhydroparthenin ( 5 ), a dihydro‐deoxygenated product ( 6 ), a formate ( 7 ) and its corresponding alcohol ( 8 ) and acetate ( 9 ), a rearranged product ( 10 ), lactone ( 11 ) and hemiacetal ( 12 ). All these derivatives, along with parthenin, were tried for their antifeedant action against sixth‐instar larvae of Spodoptera litura, for insecticidal activity against the adults of store grain pest Callosobruchus maculatus, for phytotoxic activity against Cassia tora, and for nematicidal activity against the juvenile stage‐II (J₂) of the root knot nematode Meloidogyne incognita. Antifeedent bioassay revealed that parthenin is moderately antifeedant. Among the derivatives, the saturated lactone ( 11 ) was found to be about 2.25 times more active than parthenin. The pyrazoline adduct ( 2 ) was found to be the most effective as an insecticide, with LC₅₀ values after 24, 48 and 72 h of 96, 43 and 32 mg litre⁻¹, respectively, which are comparable with neem extract. Compound 4 was found to be the most effective inhibitor of germination and seedling growth of C tora, with ID₅₀ values for germination, plumule length and radicle length of 136, 326 and 172 compared with 364, 738 and 427 mg litre⁻¹, respectively, for parthenin. Compound 10 was found to be the most effective in terms of nematicidal activity. The LC₅₀ values for this compound were 273 and 104 mg litre⁻¹, respectively, after 48 and 72 h compared with 862 and 512 mg litre⁻¹ observed for parthenin after 48 and 72 h. © 2001 Society of Chemical Industry     

Susceptibility pattern and development of resistance in the diamondback moth,Plutella xylostella L,to Bacillus thuringiensis Berl var kurstaki in India

Base‐line susceptibility for six‐day‐old larvae of the diamondback moth, Plutella xylostella, against Bacillus thuringiensis var kurstaki (Biobit^®) was studied by a cabbage leaf disc dip bioassay technique. Diamondback moth from 13 locations in seven different states spread over a distance of about 3000 km longitudinally was used for these studies. Forty‐eight‐hour LC₅₀ values varied from 1.0 to 10.97 mg AI litre⁻¹. Further investigations on the development of resistance under laboratory conditions showed an increase in LC₅₀ from 2.76 (for unselected F₁ generation) to 5.28 mg AI litre⁻¹ (for selected F₉ generation), using a selection concentration of 6.4 mg AI litre⁻¹. This suggested a possibility of the development of resistance under field conditions if there were to be extensive and indiscriminate use of B thuringiensis. These findings are discussed in relation to integrated pest management and the mechanisms of resistance in resistance management tactics. © 2000 Society of Chemical Industry     

Biodegradation of the Organophosphate Insecticide Coumaphos in Highly Contaminated Soils and in Liquid Wastes

Approximately 400000 litres of cattle dip wastes containing approximately 1500 mg litre⁻¹ of the organophosphate insecticide coumaphos are generated yearly along the Mexican border from a USDA program designed to control disease-carrying cattle ticks. Use of unlined evaporation pits for the disposal of these wastes has resulted in highly contaminated soils underlying these sites. Previous work has shown that microbial consortia present in selected dip wastes can be induced to mineralize coumaphos. Our results demonstrate that similar microbial consortia are present in coumaphos-contaminated soils from eight waste sites and that these organisms are capable of mineralizing cou-maphos in these soils using soil slurries to less than 1 mg litre⁻¹ in 7–10 days at 28°C. In addition, our results show that these consortia are able to colonize pea gravel in trickling gravel filters and can be used in these filters to metabolize coumaphos from dip wastes to less than 0·1 mg litre⁻¹ in 7–10 days at 28°C. These simple systems offer potential low cost means to detoxify coumaphos-containing wastes and to bioremediate soils contaminated with this organophosphate compound.