Potential of some Metarhizium anisopliae isolates for control of Culex quinquefasciatus (Dipt., Culicidae)

Abstract: The potential of some isolates of Metarhizium anisopliae and Beauveria bassiana for use in the integrated management of Culex quinquefasciatus was evaluated. Metarhizium anisopliae isolate 1037 was selected in initial bioassays with a 50% lethal concentration (LC₅₀) of 1.97 × 10⁴ conidia/ml. This fungus caused higher mosquito larva mortality when applied as a conidial suspension to the surface of the water than as dry conidia, with a time to 50% lethal (LT₅₀) of 1 day compared with 3.6 days for the dry conidial application. However, results with UV- and heat-inactivated conidia did not confirm a possible role of fungal toxins in causing mortality when ingested by C. quinquefasciatus larvae. Metarhizium anisopliae did not remain active for as long as the bacterium Bacillus sphaericus isolate 2362. At 24 h after application, the fungus-induced mortality on mosquito larvae was significantly lower than the mortality caused by the bacterium. By the second day, almost no activity by the fungus was observed. Results suggest that M. anisopliae isolate 1037 has potential for use in mosquito control programmes.     

Parasporal bodies of Bacillus thuringiensis subsp. morrisoni (PG-14) and Bacillus thuringiensis subsp. israelensis are similar in protein composition and toxicity

Abstract The mosquitocidal parasporal bodies of the PG-14 isolate of Bacillus thuringiensis ssp. morrisoni and B. thuringiensis ssp. israelensis were purified on sodium bromide gradients and compared using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) electron microscopy and bioassays against mosquito larvae. The parasporal bodies of both subspecies were spherical/ovoidal, approx. 0.7–1.2 μm in diameter, and contained major proteins of 28, 65, 126 and 135 kDa. In addition to these, the parasporal body of B. thuringiensis ssp. morrisoni contained at least one other major protein, of 144 kDa, which correlated with the presence of a quasi-bi-pyramidal inclusion not present in the B. thuringiensis ssp. israelensis parasporal body. The LC₅₀ for parasporal bodies of each subspecies was in the range of 3 ng/ml for fourth-instars of Aedes aegypti . These results indicate that B. thuringiensis Serotype 8a:8b, which is generally considered to produce proteins toxic to lepidopterous insects, is capable of producing a protein toxin complement similar to B. thuringiensis Serotype 14.     

Larvicidal and smoke repellency effect of Toddalia asiatica and Aegle marmelos against the dengue vector, Aedes aegypti (Insecta: Diptera: Culicidae)

Investigations were made to evaluate the larvicidal activity and smoke repellent potential of Toddalia asiatica (L.) and Aegle marmelos at different concentrations (20, 40, 60, 80 and 100 p.p.m.) against first to fourth instar larvae and pupae of Aedes aegypti (L.). The LC₅₀ of A. marmelos and T. asiatica against first instars was 50.960 and 47.893 p.p.m., respectively; against second instars, 52.979 and 50.922; third instars, 56.653 and 54.461; and fourth instars, 60.778 and 61.278. The LC₅₀ and LC₉₀ for A. marmelos and T. asiatica against pupae were 56.634 and 112.992, and 53.64 and 116.22 p.p.m., respectively. The smoke toxicity of T. asiatica against Ae. aegypti was greater than that of A. marmelos . Smoke-exposed gravid females oviposited fewer eggs when compared to those that were not exposed to smoke. Smoke-exposed females hatched a lower percentage of eggs compared to unexposed females.     

Respective role of the 42- and 51-kDa components of the Bacillus sphaericus toxin overexpressed in Bacillus thuringiensis

Abstract The 42- and 51-kDa protein genes of Bacillus sphaericus 1593 have been subcloned independently downstream from the cytA gene promoter of Bacillus thuringiensis serovar israelensis and introduced into a non-mosquitocidal strain of Bacillus thuringiensis . Consequently, each protein was overproduced and accumulated as inclusion bodies which were purified. For the first time, the 42-kDa protein inclusions alone were found to be toxic to Culex pipiens larvae (LC₅₀ at 48 h 300 ng ml⁻¹); in contrast, the 51-kDa protein inclusions were not. Moreover, a synergistic effect between these two components was observed.     

Production of Cry11A and Cry11Ba toxins in Bacillus sphaericus confers toxicity towards Aedes aegypti and resistant Culex populations.

Cry11A from Bacillus thuringiensis subsp. israelensis and Cry11Ba from Bacillus thuringiensis subsp. jegathesan were introduced, separately and in combination, into the chromosome of Bacillus sphaericus 2297 by in vivo recombination. Two loci on the B. sphaericus chromosome were chosen as target sites for recombination: the binary toxin locus and the gene encoding the 36-kDa protease that may be responsible for the cleavage of the Mtx protein. Disruption of the protease gene did not increase the larvicidal activity of the recombinant strain against Aedes aegypti and Culex pipiens. Synthesis of the Cry11A and Cry11Ba toxins made the recombinant strains toxic to A. aegypti larvae to which the parental strain was not toxic. The strain containing Cry11Ba was more toxic than strains containing the added Cry11A or both Cry11A and Cry11Ba. The production of the two toxins together with the binary toxin did not significantly increase the toxicity of the recombinant strain to susceptible C. pipiens larvae. However, the production of Cry11A and/or Cry11Ba partially overcame the resistance of C. pipiens SPHAE and Culex quinquefasciatus GeoR to B. sphaericus strain 2297.     

Ingestion, dissolution, and proteolysis of the Bacillus sphaericus toxin by mosquito larvae

Larvae of Culex quinquefasciatus are much more susceptible to the toxin of Bacillus sphaericus than are larvae of Aedes aegypti. In the present study, the rate of ingestion, dissolution, and the cleavage by midgut proteases of the B. sphaericus toxin were compared in larvae of these species to determine whether these factors account for the differences in susceptibility. During filter feeding, larvae of both species removed significant quantities of B. sphaericus toxin from suspensions. Filtration rates for 1 hr, the time at which C. quinquefasciatus exhibited marked intoxication, were higher for A. aegypti (576-713 microliters/larva/hr) than for C. quinquefasciatus (446-544 microliters/larva/hr). Within 24 hr of exposure, A. aegypti larvae ingested 97-99% of the toxin particulates and suffered not more than 10% mortality in suspensions which induced complete mortality in C. quinquefasciatus within 2 hr of exposure. Quantification of the particulate toxin present in larvae after exposure to B. sphaericus suspensions revealed that larvae of both species contained only minor amounts of the toxin, suggesting the larvae had been able to solubilize the toxin after ingestion. Proteases recovered from the feces of larvae cleaved at 43-kDa protein isolated from B. sphaericus toxin extract to 40 kDa in both species. Thus, differences in susceptibility to the B. sphaericus toxin between A. aegypti and C. quinquefasciatus are not due to differences in rates of ingestion, dissolution, or the specificity of proteases.     

Inheritance of resistance and cross resistance pattern in indoxacarb-resistant diamondback moth Plutella xylostella L.

Leaf-dip assay of Plutella xylostella against indoxacarb showed that the concentration that produced 50% mortality (LC₅₀) of indoxacarb ranged from 20.1 to 11.9 ppm, with highest in Nasik and lowest levels in Coimbatore strains. In selection studies, the LC₅₀ of indoxacarb was 18.5 ppm at generation 1 (G1), which increased to 31.3-fold (167.8 ppm) resistance after ten exposed generations (G10) as compared to unexposed. The LC₅₀ of quinalphos was 74.4 ppm, which increased to 10.0-fold (631.5 ppm) resistance after G10. The LC₅₀ of cypermethrin resistant strain resulted in an 11.5-fold increase in resistance after G10. In P. xylostella , heritability (h²) after ten generations of selection was estimated at 0.4. The number of generations required for tenfold increase in LC₅₀ (1/R) were 6.7. The response to indoxacarb selection in P. xylostella was 0.2 and the selection differential was estimated as 0.4. The phenotypic standard deviation was 0.2. Reciprocal crosses between indoxacarb-resistant and susceptible strains showed that the inheritance of indoxacarb resistance was autosomal. The degree of heritability (D_LC) (0.4, 0.4) indicated incomplete recessive inheritance of indoxacarb resistance.     

Ovicidal and larvicidal effectiveness of several insect growth inhibitors and regulators on the codling moth Cydia pomonella L. (Lep., Tortricidae)

Several insect growth inhibitors (IGIs) and regulators (IGRs) were tested in the laboratory for their ovicidal and larvicidal properties on the codling moth C. pomonella , by dipping apples in solutions of them. The IGIs which block chitin synthesis – diflubenzuron, hexaflumuron and teflubenzuron – were noticeably more effective against eggs than on newborn larvae with preventive ovicidal 50% lethality concentrations (LC₅₀) values of approximately 0.6, 1.3 and 15 p.p.m., respectively, and larvicidal LC₅₀ values of 104, 1208 and 204 p.p.m. Flufenoxuron, on the other hand, is almost as effective on larvae (LC₅₀ : 9.9 p.p.m.) as on eggs (LC₅₀ : 5.4 p.p.m.). Fenoxycarb, an IGR juvenile hormone analogue, acts as an excellent ovicidal product with an LC₅₀ value of 0.05 p.p.m. Tebufenozide, an IGR ecdyson (moulting hormone) agonist, is exclusively larvicidal with an LC₅₀ at 0.4 p.p.m. Methoxyfenozide, an IGR of the same family and currently being developed, acts as effectively on eggs as on larvae with ovicidal and larvicidal LC₅₀ values of about 0.6 and 0.8 p.p.m., respectively. When ovicidal products are applied as a curative treatment on eggs less than 24 h old, their effectiveness is much lower than that obtained from preventive application.     

Susceptibility of various developmental stages of the maize weevil, Sitophilus zeamais Motschulsky (Col., Curculionidae) to methyl iodide in brown rice

Abstract:  The efficacy of methyl iodide (MI) as a fumigant against all developmental stages of the maize weevil, Sitophilus zeamais Motsch. was investigated. Tests were conducted with concentrations of 1.5, 1.8, 2.1, 2.4, 2.7 and 3.0 mg/l, for a 6-h exposure period. Values of LC₅₀, LC₉₅ and LC₉₉ of MI for immatures and adult stages were determined. The present laboratory tests showed that MI was toxic to various life stages of S. zeamais at relatively short exposure periods. At the LC₅₀ and LC₉₅ levels, the most susceptible stage was the egg stage followed by larvae, pupae and adults (1-day mortality). The egg was found to be most susceptible to MI, requiring 0.81 and 2.16 mg/l for 50 and 99% mortality, respectively, while the adult was most tolerant, requiring 2.30 and 3.02 mg/l for 50 and 99% mortality, respectively, based on 1-day mortality count. Pupae were less susceptible to MI than egg and larvae, requiring 1.47 and 3.19 mg/l for 50 and 99% mortality, respectively. Based on the present toxicity tests, MI has the potential for use as a fumigant to control all developmental stages of the maize weevil, S. zeamais .     

Characterization and toxicity of Bacillus thuringiensis isolates from warehouses to Spodoptera exigua (Lep., Noctuidae)

Bacillus thuringiensis was isolated from 122 of 413 samples obtained from warehouses. Eighty-seven (71.31%) of these B. thuringiensis isolates were toxic to Spodoptera exigua , causing more than 60% mortality. Twenty-seven isolates were highly toxic to S. exigua , causing more than 95% mortality. Isolates 133, 47 and 58, which belonged to serotype H₇, H₄, H₄, respectively, were more active than the other isolates and their 50% lethality concentration (LC₅₀) values were 17.93, 14.78 and 15.55  μ g/ml, respectively. The isolate 133, 47 and 58 were analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and polymerase chain reaction. The results showed that they contained ~135 and 65 kDa crystal proteins, that were similar with reference strain HD-1. Isolate 133 contained the cryIA(a) , cryIA(b) , cryIA(c) , cryIE and cryII genes whereas both isolate 47 and 58 contained the cryIA(b) , cryIA(c) , cryIE and cryII genes; but they did not contain cryIII gene.     

Characterization of Iarvicidal toxin protein from Bacillus thuringiensis serovar japonensis strain Buibui specific for scarabaeid beetles

The δ-endo toxin proteins from Bacillus thuringiensis which kill the larvae of various scarabaeid beetles such as Anomala cuprea, A. rufocuprea and Popillia japonica were purified by DEAE ion exchange chromatography. A protein with a molecular size of 130 kDa was purified. During the purification a minor peak was also detected which was estimated to be 67 kDa by SDS-PAGE. Both 130 and 67 kDa proteins showed larvicidal activity against A. cuprea. The lethal concentration of the 130 kDa protein which killed 50% of the larvae tested (LC₅₀) against A. cuprea was 2 μg g¹ compost. A comparison by SDS-PAGE of the V8 protease digestion pattern of the 130 and 67 kDa larvicidal proteins showed that proteolytic resistant core peptides of approximately 60 kDa molecular size were resulted. The N -terminus amino acid sequence of the 130 and 67 kDa proteins was determined to be NH₂-XXPNNQNEYEIIDAL and NH₂-XSRNPGTFI, respectively, which is not identical to the sequence of CryIA, CryIB, CryIC and CryIII proteins.     

Improvement of Bacillus sphaericus toxicity against dipteran larvae by integration, via homologous recombination, of the Cry11A toxin gene from Bacillus thuringiensis subsp. israelensis.

Integrative plasmids were constructed to enable integration of foreign DNA into the chromosome of Bacillus sphaericus 2297 by in vivo recombination. Integration of the aphA3 kanamycin resistance gene by a two-step procedure demonstrated that this strategy was applicable with antibiotic resistance selection. Hybridization experiments evidenced two copies of the operon encoding the binary toxin from B. sphaericus in the recipient strain. The Bacillus thuringiensis subsp. israelensis cry11Aal gene (referred to as cry11A), encoding a delta-endotoxin with toxicity against Culex, Aedes, and Anopheles larvae, was integrated either by a single crossover event [strain 2297 (::pHT5601), harboring the entire recombinant plasmid] or by two successive crossover events [strain 2297 (::cry11A)]. The level of the Cry11A production in B. sphaericus was high; two crystalline inclusions were produced in strain 2297 (::pHT5601). Synthesis of the Cry11A toxin conferred toxicity to the recombinant strains against Aedes aegypti larvae, for which the parental strain was not toxic. Interestingly, the level of larvicidal activity of strain 2297 (::pHT5601) against Anopheles stephensi was as high as that of B. thuringiensis subsp. israelensis and suggested synergy between the B. thuringiensis and B. sphaericus toxins. The toxicities of parental and recombinant B. sphaericus strains against Culex quinquefasciatus were similar, but the recombinant strains killed the larvae more rapidly. The production of the Cry11A toxin in B. sphaericus also partially restored toxicity for C. quinquefasciatus larvae from a population resistant to B. sphaericus 1593. In vivo recombination therefore appears to be a promising approach to the creation of new B. sphaericus strains for vector control.     

Cyt1Ab1 and Cyt2Ba1 from Bacillus thuringiensis subsp. medellin and B. thuringiensis subsp. israelensis Synergize Bacillus sphaericus against Aedes aegypti and resistant Culex quinquefasciatus (Diptera: Culicidae).

The interaction of two cytolytic toxins, Cyt1Ab from Bacillus thuringiensis subsp. medellin and Cyt2Ba from Bacillus thuringiensis subsp. israelensis, with Bacillus sphaericus was evaluated against susceptible and resistant Culex quinquefasciatus and the nonsensitive species Aedes aegypti. Mixtures of B. sphaericus with either cytolytic toxin were synergistic, and B. sphaericus resistance in C. quinquefasciatus was suppressed from >17,000- to 2-fold with a 3:1 mixture of B. sphaericus and Cyt1Ab. This trait may prove useful for combating insecticide resistance and for improving the activity of microbial insecticides.     

Molecular cloning of the 130-kilodalton mosquitocidal delta-endotoxin gene of Bacillus thuringiensis subsp. israelensis in Bacillus sphaericus

A 3.7-kilobase (kb) XbaI fragment harboring the cryIVB gene (L. Thorne, F. Garduno, T. Thompson, D. Decker, M. A. Zounes, M. Wild, A. M. Walfield, and T. J. Pollock, J. Bacteriol. 166:801-811, 1986) which encoded a 130-kilodalton (kDa) mosquitocidal toxin from a 110-kb plasmid of Bacillus thuringiensis subsp. israelensis 4Q2-72 was cloned into pUC12 and transformed into Escherichia coli. The clone with a recombinant plasmid (designated pBT8) was toxic to Aedes aegypti larvae. The fragment (3.7 kb) was ligated into pBC16 (tetracycline resistant [Tcr]) and transformed by the method of protoplast transformation into Bacillus sphaericus 1593 and 2362, which were highly toxic to Anopheles and Culex mosquito larvae but less toxic to Aedes larvae. After cell regeneration on regeneration medium, the Tcr plasmids from transformants (pBTC1) of both strains of B. sphaericus were prepared and analyzed. The 3.7-kb XbaI fragment from the B. thuringiensis subsp. israelensis plasmid was shown to be present by agarose gel electrophoresis and Southern blot hybridization. In addition, B. sphaericus transformants produced a 130-kDa mosquitocidal toxin which was detected by Western (immuno-) blot analysis with antibody prepared against B. thuringiensis subsp. israelensis 130-kDa mosquitocidal toxin. The 50% lethal concentrations of the transformants of strains 1593 and 2362 against A. aegypti larvae were 2.7 X 10(2) and 5.7 X 10(2) cells per ml, respectively. This level of toxicity was comparable to the 50% lethal concentration of B. thuringiensis subsp. israelensis but much higher than that of B. sphaericus 1593 and 2362 (4.7 X 10(4) cells per ml) against A. aegypti larvae.(ABSTRACT TRUNCATED AT 250 WORDS)     

球形芽孢杆菌TS—1灭蚊毒蛋白的酶联免疫吸附测定

Bacillus sphaericus Ts-1 Mosquito larvicidal toxins 42 k Da and 43 k Da were isolated by Sephadex G-200 chromatography. Three strains of highly toxic B. sphaericus and two non toxic strains were screened for toxic proteins using ELISA. The lowest detectable toxin level was 1.56 X 10(-5) mg/ml. Non toxic strains did not produce antigens reacting to either the 42 kDa or the 43 kDa antibodies. Ts-1 cultures were examined at 12 and 24 h by LC50 bioassay against Culex pipiens. The LC50's at 12 h and 24 h were 0.71 ppm and 0.154 ppm, respectively, i.e., the toxin level at 24 h was 4.6 times the level at 12 h. ELISA tests established total toxin at 0.049 mg/ml and 0.225 mg/ml at 12 h and 24 h, respectively, confirming the LC50 study.     

Molecular cloning of the 130-kilodalton mosquitocidal delta-endotoxin gene of Bacillus thuringiensis subsp. israelensis in Bacillus sphaericus.

A 3.7-kilobase (kb) XbaI fragment harboring the cryIVB gene (L. Thorne, F. Garduno, T. Thompson, D. Decker, M. A. Zounes, M. Wild, A. M. Walfield, and T. J. Pollock, J. Bacteriol. 166:801-811, 1986) which encoded a 130-kilodalton (kDa) mosquitocidal toxin from a 110-kb plasmid of Bacillus thuringiensis subsp. israelensis 4Q2-72 was cloned into pUC12 and transformed into Escherichia coli. The clone with a recombinant plasmid (designated pBT8) was toxic to Aedes aegypti larvae. The fragment (3.7 kb) was ligated into pBC16 (tetracycline resistant [Tcr]) and transformed by the method of protoplast transformation into Bacillus sphaericus 1593 and 2362, which were highly toxic to Anopheles and Culex mosquito larvae but less toxic to Aedes larvae. After cell regeneration on regeneration medium, the Tcr plasmids from transformants (pBTC1) of both strains of B. sphaericus were prepared and analyzed. The 3.7-kb XbaI fragment from the B. thuringiensis subsp. israelensis plasmid was shown to be present by agarose gel electrophoresis and Southern blot hybridization. In addition, B. sphaericus transformants produced a 130-kDa mosquitocidal toxin which was detected by Western (immuno-) blot analysis with antibody prepared against B. thuringiensis subsp. israelensis 130-kDa mosquitocidal toxin. The 50% lethal concentrations of the transformants of strains 1593 and 2362 against A. aegypti larvae were 2.7 X 10(2) and 5.7 X 10(2) cells per ml, respectively. This level of toxicity was comparable to the 50% lethal concentration of B. thuringiensis subsp. israelensis but much higher than that of B. sphaericus 1593 and 2362 (4.7 X 10(4) cells per ml) against A. aegypti larvae.(ABSTRACT TRUNCATED AT 250 WORDS)     

Larvicidal toxicity of Japanese Bacillus thuringiensis against the mosquito Anopheles stephensi

Japanese isolates of Bacillus thuringiensis were screened for larvicidal activity against the mosquito Anopheles stephensi , the urban malaria vector of the Indian subcontinent. Among more than 30 strains identified, larvicidal activity causing >80% mortality in 72 h was demonstrated for 41/1449 (2.8%) isolates. The majority of strains and isolates (97.2%) exhibited little or no larvicidal activity. Anopheles -active strains belonged to more than 12 H serotypes, especially H3ade (serovar fukuokaensis ) and H44 (serovar higo ). SDS-PAGE profiles of inclusion proteins showed 4 distinct types among 6 active strains examined. The most active Japanese isolates were H20 strain 89-T-34-14 (LC₅₀ 4.4 μg/ml) and H44 serovar higo strain 74-E-45-24 (LC₅₀ 7.6 μg/ml), respectively, 13-fold and 23-fold less active than the international standard H14 serovar israelensis (LC₅₀ 0.33 μg/ml).     

Identification of entomopathogenic Bacillus isolated from Simulium (Diptera, Simuliidae) larvae and adults.

Entomopathogenic bacteria isolated from Simulium larvae and adults from breeding sites in the states of S?o Paulo and Rio de Janeiro, Brazil, were identified as 18 strains of Bacillus thuringiensis and one of B. sphaericus. Most of these strains were serotyped according to their flagellar antigens. However, nine of the B. thuringiensis samples, could not be serotyped and were designated as "autoagglutinating"; they were also shown to be toxic in preliminary tests against Aedes aegypti larvae. Additionally, B. sphaericus was also shown to be toxic towards Culex quinquefasciatus larvae.     

Seasonal and geographical toxicity of Indoxacarb against Helicoverpa armigera and influence of different host plants against Indoxacarb in India, 2005–2007

Indoxacarb, an oxadiazine insecticide, was evaluated for its effectiveness against Helicoverpa armigera collected from selected locations in India. Determination of Indoxacarb efficacy was done using a log-dose probit (LDP) bioassay against third instars collected from cotton ( Gossypium arborium ) fields near Akola, India. Monthly levels of toxicity of Indoxacarb were determined from July 2005 to March 2007. The maximum tolerance level of Indoxacarb was reported for the Amaravati strain (5.09 p.p.m.) and the minimum tolerance level for the Fatehbad strain (0.22 p.p.m.). Seasonal monitoring of Indoxacarb toxicity revealed an increased trend in tolerance from July 2005 to February 2006, which decreased from March 2006. The LC₅₀ of Indoxacarb was 2.71 p.p.m. in July 2005 and 17.14 p.p.m. in February 2006. During 2006–2007, the LC₅₀ was 3.84 p.p.m. at the start of the season and in March 2007 it was 13.51 p.p.m. The minimum LC₅₀ of Indoxacarb was reported for H. armigera larvae fed on Legasca spp. (1.62 p.p.m.) and the maximum LC₅₀ was reported for H. armigera reared on chickpea ( Cicer arietium ) (8.45 p.p.m.). LC₅₀ of 2.73 and 4.56 p.p.m. were reported for H. armigera fed on cotton ( Gossypium arborium ) and pigeonpea ( Cajanus cajan ), respectively.     

Proteolysis in the gut of mosquito larvae results in further activation of the Bacillus sphaericus toxin

Gut proteases from the larvae of the mosquito Culex pipiens convert the 43-kilodalton (kDa) toxin from Bacillus sphaericus 2362 to a 40-kDa peptide. The 50% lethal concentration of this peptide for tissue culture-grown cells of Culex quinquefasciatus was 1.0 microgram/ml (as determined by the intracellular ATP assay), 54-fold less than that of the 43-kDa peptide. Gut proteases from Anopheles gambiae and Aedes aegypti, as well as bovine pancreatic trypsin, also converted the 43-kDa protein to a 40-kDa peptide which was indistinguishable from the peptide formed by the proteases from C. pipiens with respect to its toxicity to tissue culture-grown cells of C. quinquefasciatus. Evidence for the in vivo conversion of the 43-kDa protein to the 40-kDa peptide was also obtained from experiments in which larvae of C. pipiens, Anopheles gambiae, and Aedes aegypti were fed crystals from B. sphaericus 2362. By using the exclusion of trypan blue as an indication of cell viability, it was shown that chitobiose, chitotriose, N-acetylmuramic acid, and N-acetylneuraminic acid decreased the toxicity of the 40-kDa peptide (from 100 to 50% mortality at about 10 mM concentrations of these sugars). Muramic acid, N-acetylgalactosamine, and N-acetylglucosamine were less effective, while several sugars had no effect, suggesting that the 40-kDa toxin binds to specific receptors on the cell membrane. The 40-kDa protein was less toxic to tissue culture-grown cells of Anopheles gambiae and Aedes dorsalis, and the same sugars which reduced the toxicity for cells of C. quinquefasciatus were also effective in reduction of toxicity for these cell lines.(ABSTRACT TRUNCATED AT 250 WORDS)