Microbial Insecticides Research Articles

Field Evaluation of Microbial and Chemical Insecticides for Diamondback Moth and Other Lepidopterous Pests Control on Cabbage

The newly introduced experimental Bacillus thuringiensis (BT) pro-ducts and one synthetic chemical were screened in field on their efficacies to control the diamondback moth (DBM, Plutella xylostella), Spodoptera litura and Pieris rapae, and the long-used BT products and synthetic pyrethroids served as the comparing control agents. The results of two field experiments indicated that the newly commercialized SAN415-SC and other experimental BT products such as Florbac-FC, Florbac-XLV, TC0918 and CGA237218 provided better control on the DBM than other brands although suitable dosages still need to be determined. All BT products provided fair control for P. rapac. A newly developed thiourea insecticide/acaricde, Polo (diafen thiuron), performed better than any other entries in this field evaluation on both DBM and S. litura. Two tested synthetic pryethroids had not only lost their abi1iy in controlling the DBM, also resulted in higher DBM counts by reducing both competition from other pests and the parasitization of natural enemies.

Germination and multiplication of Bacillus thuringiensis var. kurstaki in the midgut of Pieris canidia larva: An Electron Microscopic study

Presently Bacillus thuringiensis var. kurstaki (Btk, thuricide) is a popular microbial insecticide on market for controlling lepidopterous pests. The damage of Btk on lepidopterous larvae have been well documented. However, practically few references give sufficient ultrastructural details on the germination and multiplication of Bt spores and bacterial cells after infecting the larvae. The present study is aimed to fill the gap of the necessary information.Pieris canidia L. larvae were immersed in 2.5% (w/v) thuricide (40,000 IU, Sandoz Co.) spore-crystal suspension for 5 sec. dip and were put onto petri dishes for observation in various time intervals after blotted dry with filter paper. Control larvae had not been treated with Btk.

Effect of water potential, temperature, and clay-coating on survival of Beauveria bassiana conidia in a loam and peat soil

When Beauveria bassiana conidia were mixed in nonsterile Yolo fine sandy loam (YFSL) or Staten peaty muck (peat) soil at water potentials ranging from 0.0 bars (saturation) to −1500 bars, conidia half-lives were longest at −15 bars and decreased as the water potential approached either 0.0 or −200 bars. Conidia half-lives increased as the water potential decreased from −200 to −1500 bars. Conidia half-lives were longest at a soil temperature of 10°C and decreased both at 2°C and as the temperature approached 50°C where no conidia were recovered after 2 weeks. The longest mean half-life value was 44.4 weeks for conidia in YFSL at −10 bars and 10°C; the shortest half-life value was 0.3 weeks in peat soil at 0 bars and 28°C. Clay-coating lengthened conidia survival in all treatments in a factorial experiment involving the two soil types and several combinations of soil temperature and water potential. When two strains of B. bassiana were compared, colony counts of strain ABG-6178 always decreased relative to an initial baseline count taken soon after mixing conidia and soil; colony counts of strain IL-116 routinely increased after the baseline count was taken before decreasing later. Conidia survival was often significantly longer in the low organic YFSL than in the high organic peat. The results suggest that conidia survival is influenced by the direct effect of physical factors and soil microbial populations. Since B. bassiana conidia survival is highly variable, its potential as a microbial insecticide is much greater in some soil environments than in others.

微生物殺虫剤Ｂａｃｉｌｌｕｓ ｔｈｕｒｉｎｇｉｅｎｓｉｓの現状と将来

微生物殺虫剤Ｂａｃｉｌｌｕｓ ｔｈｕｒｉｎｇｉｅｎｓｉｓの現状と将来

Microbial insecticides in Nigeria: State of the art

The term “microbial insecticides” is defined here in the broad sense to include microbial metabolites or entomopoisons produced by micro-organisms. Examples include Bacillus thuringiensis delta-endotoxin which is very active against many lepidopterous and dipterous larvae, beauvericin, a toxic metabolite of the fungus, Beauveria bassiana, and other entomopathogens which might not produce any toxic metabolite at all but arc mass-produced, formulated, and ‘ applied as conventional insecticides. As of now, microbial insecticides are not in operational use in Nigeria. However, there is a basis for the detection, isolation, and subsequent development of naturally occur in entomopathogens. Different commercial products have also been tested if only on a small scale in the laboratory or field. This paper reviews the beginnings of insect pathology/microbial control in Nigeria. It also discusses the, advantages, prospects and problems of microbial insecticides as a component of integrated pest management in agriculture and public health in this part of the world.

Localization of Bacillus thuringiensis Kurstaki toxin binding sites by means of BT toxin gold probes

Strains of the bacterium Baci11us thuringiensis (Bt) produce toxins which, when ingested by susceptible larvae, function as a microbial insecticide. In addition to this broad spectrum activity against lepidopteran and dipteran larvae, the toxin has no effect on humans, animals and beneficial insects. As a corollary to our effort to genetically engineer Bt toxin production in major crop plants, we have studied the basic toxin-membrane interactions in the midgut region of Manduca sexta (tobacco hornworm) larvae by means of Bt toxin coated colloidal gold probes.The midgut of 2nd instar M.sexta larvae was removed, incised along its length, inverted and incubated for minimal time in phosphate buffer. Bt gold probes were produced by incubating 15nm diameter colloidal gold in the purified 68kDa active toxin fragment. Dissected midgut was placed in drops of Bt toxin gold solution for 1, 4, 8, 16, and 32min. The samples were fixed for 3hr in 2% glutaraldehyde, post-fixed in 1 % osmium tetroxide, dehydrated in a graded ethanol series and embedded in Embed 812.

Implantation of Acephate and Injection of Microbial Insecticides into Pin Oaks for Control of Gypsy Moth: Time and Efficacy Comparisons

The efficacy and temporal pattern of gypsy moth mortality resulting from implantation and injection of pin oaks with synthetic organic (acephate) and microbial (gypsy moth nucleopolyhedrosis virus = NPV, and Bacillus thuringiensis Berliner = B.t.) insecticides was investigated. All mortality occurred in the larval stage. Implantation of acephate produced significant increases in cumulative mortality. Neither microbial treatment showed a significant increase in mortality over controls. In all acephate treated trees, and in one of three B.t. treated trees, there was an exponential sigmoid pattern of increase in cumulative mortality over time. There was considerable variation among trees. In the acephate treatment, this was expressed as variation in the lag-time of a sigmoid mortality pattern. In the S.f. treatment, larvae on only one of three trees showed a mortality response. The successful use of implantation of acephate in this and other recent papers suggest that this technology will undoubtedly have a place in gypsy moth integrated pest management programs in urban environments. Further work to determine the reasons for the lack of success with the microbials is warranted.

Analysis of the genotoxic activity of Bacillus thuringiensis β-exotoxin by means of the Drosophila wing spot test

The β-exotoxin (Thuringiensin) produced by some strains of serotypes of Bacillus thuringiensis was subjected to the somatic mutation and recombination test in Drosophila melanogaster. Larvae transheterozygous for two recessive mutations of wing trichomes, mwh and flr 3, developed in medium containing 1.0, 0.5, or 0.1 ppm of pure β-exotoxin (LC 50 0.85 ppm). Wings of emerged adult females were analyzed for the presence of phenotypically mutant mosaic spots. For comparison, the commercial microbial insecticide Bitoxibacillin containing 0.6 – 0.8% of β-exotoxin was also tested. In this case, larvae were exposed to 0.014% of the autoclaved supernatant of Bitoxibacillin (LC 50 0.01%). No mutagenic or recombinogenic effects of the test compounds were observed. The results indicate that β-exotoxin does not exhibit any genotoxic activity which could limit its practical use as a suitable agent for insect pest control.

Inactivation of Nonoccluded and Occluded Baculoviruses and Baculovirus-DNA Exposed to Simulated Sunlight

Natural sunlight is the most significant environmental factor affecting the stability of microbial insecticides formulated from occluded entomopathogenic viruses. Theoretically the crystalline protein matrix that occludes and surrounds each virion containing DNA should provide some protection against inactivation by sunlight-UV. No significant differences, however, were obtained in either the extent or rate of inactivation when nonoccluded, polyhedra derived virions (PDV) and tissue culture derived virions (TCNOV), or virions occluded in polyhedral inclusion bodies (PIBOV) of the Singly-enveloped nuclear polyhedrosis virus of Heliothis species (HzSNPV) were exposed to a simulated sunlight-UV source (SUV). The residual half-life of PDV, TCNOV, and PIBOV, as measured by bioassay against susceptible larvae of Heliothis virescens , was 6.3, 6.3, and 5.8 h, respectively. There was smearing of the EcoRI restriction enzyme (REN) patterns and an increase in lower molecular-weight species after exposure to SUV of both naked viral DNA and DNA of virions occluded in polyhedral inclusion bodies (PIB). Production of higher molecular-weight species of DNA, however, only was detected in DNA from PIBOV exposed to SUV. Changes in REN patterns of viral DNA were never detected with shielded-exposed HzSNPV.

Control on Potato, 1988:

Abstract Potatoes were planted on 9 May in South Deerfield, Mass. Soil type was a fine sandy loam, pH 5.6. CPB pressure was heavy because potatoes were grown adjacent to overwintering sites. Treatments were replicated 4 times in a randomized complete block design. Each plot consisted of two 30-ft rows with a 6-ft fallow area separating each plot. Treatments were applied with CO2-pressurized sprayers at 40 psi delivering 70 gal/acre. Applications were made on 20 and 28 Jun, 5 and 18 Jul, and 3 Aug. Monitor 4 LC was applied to all treatments on 20 Jul at MRFR to control aphids and leafhoppers. CPB population densities were determined by counting larvae on 5-10 whole stalks in each plot. To adequately evaluate microbial insecticides, larvae were counted and recorded as early instars (first and second) or late instars (third and fourth). The performance of microbial materials was evaluated primarily by comparing late-instar counts because it took 4-5 d for dead larvae to drop from the plants. On 22 Jul, each plot was rated for defoliation on a scale of 0-100%.

Control on Potato, 1988:

Abstract Potatoes were planted on 9 May in South Deerfield, Mass. Soil type was a fine sandy loam, pH 5.6. CPB pressure was heavy because potatoes were grown adjacent to overwintering sites. Treatments were replicated 4 times in a randomized complete block design. Each plot consisted of two 30-ft rows with a 6-ft fallow area separating each plot. Treatments were applied with CO2-pressurized sprayers at 40 psi, delivering 70 gal/acre. Applications were made on 21 and 28 June and 5 and 18 Jul. Monitor 4 LC was applied to all treatments on 20 Jul at MRFR to control aphids and leafhoppers. CPB population densities were determined by counting larvae on 5-10 whole stalks in each plot. To adequately evaluate microbial insecticides, larvae were counted and recorded as early instars (first and second) or late instars (third and fourth). The performance of these materials was evaluated primarily by comparing late-instar counts, because it took 4-5 days for the dead larvae to drop from the plants. On 22 Jul, each plot was rated for defoliation on a scale of 0-100%. At that time, the control plots were completely defoliated.

Potato Insect Control, 1988:

Abstract Potatoes were planted on 9 May in South Deerfield, Mass. Soil type was a fine sandy loam, pH 5.6. CPB pressure was heavy because potatoes were grown adjacent to CPB overwintering sites. Treatments were replicated 4 times in a randomized complete block design. Each plot consisted of two 30-ft rows with a 6-ft fallow area separating each plot. Treatments were applied with CO2-pressurized sprayers at 40 psi, delivering 70 gal/acre. Applications were made on 21 and 28 Jun and 8 and 15 Jul. CPB population densities were determined by counting larvae on 5-10 whole stalks/plot. To evaluate microbial insecticides, larvae were counted and recorded as early instars (first and second) or late instars (third and fourth). The performance of these materials was evaluated primarily by comparing late instar counts, as it took 4-5 d for the dead larvae to drop from the plants. On 20 Jul, the leafhoppers were counted on 5 leaves/plot. On 20 Jul, each plot was rated for defoliation on a scale of 0-100%.

EFFECTIVENESS OF MICROBIAL AND CHEMICAL INSECTICIDES IN CONTROL OF THE COLORADO POTATO BEETLE (COLEOPTERA: CHRYSOMELIDAE) ON POTATOES AND TOMATOES

AbstractThe control of the Colorado potato beetle, Leptinotarsa decemlineata (Say), by formulations of Bacillus thuringiensis (Berliner) (B.t.) and other microbial agents and chemical insecticides was assessed in field plots of potatoes and tomatoes over a 5-year period. Applications of formulations of thuringiensin, the beta exotoxin of B.t., and of B.t. var. son diego (B.t.sd.) to potatoes reduced numbers of larvae of the potato beetle compared with the nontreated check and resulted in yields significantly greater than from the check plots and, in most cases, similar to yields from plots treated with carbofuran. Treatment of tomatoes with B.t.sd. reduced populations of larvae of the Colorado potato beetle compared with the nontreated check and increased yield of nondamaged fruit from plots. An initial application of carbofuran to potatoes or permethrin to tomatoes followed by applications of thuringiensin or B.t.sd. protected potatoes or tomatoes as well as did the chemical insecticide used alone in a treatment program. Applications of preparations of B.t. var. kurstaki or spores of the fungus Beauveria bassiana (Balsamo) Vuillemin or the microsporidium Vairimorpha necatrix (Kramer) did not reduce populations of the beetle.

Baculoviruses: Their Status Compared to Bacillus thuringiensis as Microbial Insecticides

With the present need to address environmental problems, there is much interest in biological control of insect pests rather than the use of chemical insecticides. This article critically reviews the use of baculoviruses worldwide in agriculture and forestry, directing attention not only to intrinsic activity but to other relevant factors such as shelf-life in storage, fluctuation in demand, and cost of production and applications. It draws particular attention to the relevance of baculoviruses to pest control in developing countries where labour is cheap.

Control of Tomato Hornworms on Tobacco with Microbial Insecticides and An Insect Growth Regulator, 1986

Abstract Two microbial insecticides and an insect growth regular were evaluated in the laboratory and field for control of tomato hornworms on tobacco at the Research Station, Agriculture Canada, Delhi, On. Tobacco seedlings were transplanted on 26 May. Plots, 20.0 × 3.5 ft, were arranged in a randomized block design with 2 replications. Each plot was a single row of 10 plants. Materials were applied to the upper and lower surfaces of tobacco leaves using a Knapsack sprayer with an adjustable nozzle at a rate of 40 gal/acre on 14 Aug. Test insects were 3rd- and 4th-instar larvae of the tomato hornworm collected from tobacco plants in an unsprayed field. In the laboratory tests, the larvae, 10 for each replicate, were placed individually in 24-oz wide-mouth jars. Two hours after application of the insecticides, random samples of tobacco leaves were collected from each plant, taken to the laboratory, and placed in the jars with the larvae. In field tests, the larvae were placed on the treated tobacco plants in the test plots at the rate of 1 larva/plant about 3 h after treatment. In evaluating the effectiveness of the treatments, larval mortalities were assessed daily for 12 days for the laboratory tests and 4 days for the field tests. Larvae that remained on the leaves and showed any reaction when gently touched were considered alive. Abbotts formula was used to correct for the mortality occurring in the check. Before analysis of variance, data were transformed into angular units, and Duncan’s multiple range test was used to separate treatment means. Means were converted to original units for tabulation.

Compatibility of NPV of Spodoptera litura (Fabricius) With Certain Fungicides

From time to time. it has been suggested that microbial insecticides might be combined with chemical pesticides used in agriculture and forestry. Jaques (1985) suggested that the compatibility of insect viruses with pesticide chemicals especially fungicides and insecticides is important because viruses may have to be mixed with other chemicals during practical use in the field to avoid duplication of application operation. Relationships of viruses and pesticides have been reviewed by Benz (1971) and Jaques and Morris (1981).In the present study, the compatibility of S. litura NPV with mancozeb, copper oxychloride and carbendazim was studied with a view to imd out if NPV and fungicides could be applied together to manage both S. litura and foliar diseases.

The glycoprotein toxin of Bacillus thuringiensis subsp. israelensis indicates a lectinlike receptor in the larval mosquito gut

The mosquito-active protein crystals produced by Bacillus thuringiensis subsp. israelensis contain covalently attached aminosugars which are critical for their larvicidal activity. The 50% lethal concentrations toward Aedes aegypti larvae were increased up to 10-fold by mild periodate treatment, up to 40-fold by forming the protein crystals in the presence of tunicamycin, and up to 7-fold by the presence during the mosquito bioassays of N-acetylglucosamine or its trimer, triacetylchitotriose. Periodate-treated crystals and crystals formed in the presence of tunicamycin had greatly reduced binding capacities for wheat germ agglutinin, an N-acetylglucosamine-specific lectin. These results suggest that the B. thuringiensis subsp. israelensis glycoprotein toxin binds to a lectinlike receptor in the larval mosquito gut. Furthermore, the distinct lectin-binding patterns exhibited by diptera-active versus lepidoptera-active B. thuringiensis crystals suggest that host specificity for the microbial insecticides is determined, in part, by the carbohydrate portion of their glycoprotein crystals.

The differential mortality at various life stages of the greenhouse whitefly, Trialeurodes vaporariorum (Homoptera: Aleyrodidae), by infection with the fungus Aschersonia aleyrodis (Deuteromycotina: Coelomycetes)

The parasitoid Encarsia formosa is commonly applied to control the greenhouse whitefly Trialeurodes vaporariorum in glasshouse tomatoes and cucumbers. Nevertheless, in some cases the control capacity of this natural enemy is insufficient and an additional selective pest-suppressing agent is desirable. The entomopathogenic fungus Aschersonia aleyrodis was applied to cucumber plants carrying whiteflies in different developmental stages. After spraying each leaf with 2 ml of spore suspension (4 × 10 6 spores/ml) the plants were kept at 100% RH for 24 hr; thereafter the humidity was lowered to 70% RH at 20°C and the photoperiod was 16 hr. Treated eggs did not become infected, but larvae that hatched from these eggs and settled on the treated abaxial leaf surface were infected at the same rate and to the same degree as treated first instar larvae. This suggests that the spores persist for at least 7 days. The final percentages of infection over all instars when treated as young eggs, old eggs, and first larval instars were 94, 93, and 90%, respectively. The final percentages of infection when treated as third and fourth larval instars and prepupae were 76, 28, and 12%, respectively. The older instars were less susceptible and adults were seldom infected by the fungus. Several applications of A. aleyrodis as a microbial insecticide are needed to achieve sufficient control of whitefly populations in glasshouses.

Safety of the entomopathogen Bacillus thuringiensis var. israelensis for mammals.

Six preparations of Bacillus thuringiensis var. israelensis de Barjac were tested for toxicity and infectivity to mice, rats, and rabbits. Oral and aerosol administration of the microbial insecticide to rats resulted in no deaths. Intraperitoneal injection of one preparation into athymic mice produced substantial mortality (26/42), but a subsequent experiment with a different preparation did not result in mortality. B. t. israelensis persisted in the spleen of mice for as long as 7 wk, but multiplication in mammals was not evident. Colony-forming units of B. t. israelensis seemed to be cleared from the host as inert particles. B. t. israelensis dusts caused minimal ocular irritation and pastes caused severe conjunctival congestion in rabbit eyes. We conclude that B. t. israelensis is not a virulent, invasive mammalian pathogen and that it can be used safely in environments where human exposure is likely to occur.

The beet armyworm in floricultural crops

Common in field and vegetable crops, the beet armyworm has invaded flower crops. It's hard to control with insecticides and can quickly build resistance. Microbial insecticides may be an effective alternative.