In an effort to develop a more effective technique in dispersing a microbial control agent, Bacillus thuringiensis (Bt), a truck-mounted ultra low volume (ULV) generator (Scorpion) was used to disperse B. thuringiensis israelensis (Bti) and Bti with malathion. Complete larval and adult mortalities for all tested mosquito species within the first 70-80 feet from the ULV generator were achieved. Beyond that distance less than 50% mortality was achieved as insufficient sprayed particles reached the area. A minimum of 10(3) Bti colony forming units per ml is required to cause 100% larval mortality. The sprayed Bti larvicidal toxins were persistent in the test water 7 days post ULV. The effectiveness of B. thuringiensis jegathesan (Btj), a new mosquitocidal Bt serotype was also evaluated. Similar mortality results as Bti were achieved except that the Btj toxins underwent degradation in the test water, since less than 50% less in larval mortality was observed in 7 days post ULV samples. This ULV method has the potential to disperse Bt and malathion effectively for a simultaneous control of mosquito adults and larvae.
There was high mortality in late larval instars of Aedes albopictus (Skuse) from laboratory and field populations in the 24 h after application of three Bactimos formulations of Bacillus thuringiensis H-14. Mortalities were higher and residual effects longer in field populations than in laboratory ones. Briquets were the most effective formulation (mortality 96-100% after five weeks; 76-92% after eight weeks). Culex quinquefasciatus Say larvae were tested only against the briquet formulation. In the laboratory, 100% mortality of late instars persisted for six weeks and dropped to 48-88% after eight weeks. In the field, late instars were reduced by 62-87% after 24 h and 69-72% after one week compared to increases in an untreated population of 160% and 176% respectively.
Bacillus thuringiensis israeliensis (BTI) against culicine mosquitoes was tried out in cement sullage drains in Kelang municipal area at a dosage of 0.15 ppm. and 0.6 ppm. The results of the trial showed that at 0.15 ppm. the BTI was not effective, but at 0.6 ppm. it was effective giving about 95% kill. There was no residual effect and treatment had to be repeated weekly.
Adulticidal and larvicidal performances of a water-based pyrethroid microemulsion Pesguard PS 102 (AI d-allethrin and d-phenothrin, both at 5.0% w/w) and Vectobac 12AS, an aqua-suspension Bacillus thuringiensis israelensis (B.t.i.) formulation (AI 1,200 ITU/mg) were assessed against mosquitoes Aedes aegypti, Aedes albopictus, and Culex quinquefasciatus using a Leco ULV Fog Generator Model 1600 and a Scorpion 20 ULV AirBlast Sprayer. Laboratory-cultured mosquito adults and larvae were used for efficacy assessment. For trials using Leco, both pyrethroid and bacterial formulations were dispersed both singly and in combination with Pesguard PS 102 at a dosage of 0.2 liters/ha and B.t.i. at a dosage of 1.0 liter/ha. Similar trials with the Scorpion were also conducted with Pesguard PS 102 at a dosage of 0.2 liters/ha and a higher dosage of B.t.i. (1.5 liters/ha). Experiments were conducted in a football field (200 x 100 m) where five check points at 10, 25, 50, 75, and 100 m downwind from the spray nozzle were chosen for efficacy assessments. Knockdown and mortality were scored at 1 and 24 h postspraying. Results from both trials showed that mortality values varied with distance from spray nozzle. For trials with Leco, fogging with the combination of Pesguard PS 102 and B.t.i. provided larvicidal mortality of > 80% for both Aedes species and of > 60% for Cx. quinquefasciatus larvae at several check points, depending on wind conditions. Complete mortality of adult Aedes mosquitoes at 24 h posttreatment was also achieved, while mortality values for Culex adults reached > 90% under strong wind conditions. As for trials with the Scorpion 20, high adult and larval mortalities were also achieved, with > 90% mortality at some check points. The above study demonstrated the possibility of achieving both larvicidal and adulticidal effects when using a combination of B.t.i. and Pesguard PS 102 in ULV space spray.
Evaluation of the effectiveness of Bacillus thuringiensis ssp. israelensis (B.t.i.) against mosquito larvae dispersed by ultralow volume (ULV) spraying was conducted in simulated field trials. Effectiveness was measured using 3 different indicators: larval mortality, colony-forming unit enumeration, and droplet analysis. B.t.i. was dispersed with a ULV generator using 2 different flow rates: 0.3 and 0.5 liter/min on 2 different days. Based on the results of this study, it can be concluded that an output of 0.3 liter/min is effective for controlling Aedes aegypti. although a dosage of 0.5 liter/min can be used when high residual activity is desired. For Culex quinquefasciatus control, both dosages were effective but with low residual activity. For Anopheles maculatus control, only a discharge rate of 0.5 liter/min was effective with low residual activity. B.t.i. application at both dosages penetrated tires well, indicating that B.t.i. ULV application is an effective method for controlling container-inhabiting mosquitoes. Good coverage of target area and penetration were attributed to satisfactory droplet profiles.
Susceptibility levels of a few laboratory-cultured and dengue-endemic area field-collected strains of Aedes aegypti and Aedes albopictus to Bacillus thuringiensis israelensis (Bti) at different storage ages were studied. The susceptibility of laboratory-cultured World Health Organization (WHO) Bora Bora reference, Vector Control Research Unit (VCRU), and Fumakilla Malaysia Berhad (FMB) strains of Ae. aegypti to Bti was examined. The sensitivity to Bti decreased with storage age. The median lethal concentration (LC50) for Bti increased by 2-3 times after 2 years compared to a fresh sample (3-6 months of storage). However, after the 2-year storage period, Bti still provided very good efficacy against all laboratory-cultured susceptible strains of Ae. aegypti and Ae. albopictus. The observed 95% lethal concentration values were about 20 times lower than the recommended concentration (6,000 international toxic units (ITU)/liter). Results obtained from the study against the dengue-endemic area field-collected strains of Ae. aegypti and Ae. albopictus confirmed the effectiveness of the Bti after storage for 2 years (18-24 months). For Ae. aegypti, the Ujung Batu strain was the most susceptible to Bti, whereas the Sungai Nibong strain showed the most tolerance. Susceptibility of laboratory-cultured strains varied; the Air Itam strain of Ae. albopictus was the most susceptible to Bti, whereas the Kampung Serani strain was the most tolerant among the field strains. However, the laboratory strain of Ae. albopictus was more susceptible than all the field strains.
The compatibility of the commercial aqueous Bacillus thuringiensis serovar israelensis (B.t.i.) formulation, Vectobac 12AS, with the chemical insecticides Actellic 50EC, Aqua Resigen, Resigen, and Fendona SC, for the simultaneous control of Aedes larvae and adults was studied by dispersing nine different formulations using a portable mist blower, in single story half-brick houses. The effectiveness of the treatment was evaluated by measuring the larval mortality, adult mortality, and droplet analysis at varying distances from the sprayer. Persistence of the larvicidal activity of the chemical insecticides and B.t.i was also determined by measuring the larval mortality in the test samples 7 days posttreatment. The sprayed particles in all the trials were 50-60 microns in size, indicating that the particles were those of mist spray. Test samples placed within 3 m from the sprayer gave the maximum larval and adult mortality. Chemical insecticides exhibited maximum larval mortality in the 1 h posttreatment test samples and it was comparable to the larvicidal activity of B.t.i. The larvicidal toxins of B.t.i were more stable and were able to affect sufficient larval mortality for 7 days posttreatment. The larvicidal activity of the mixtures, i.e., chemical insecticides with B.t.i, in the 1 h posttreatment test samples was not significantly different from the larvicidal activity of the chemical insecticides and it was comparable to the larvicidal activity of B.t.i alone. However, the larvicidal activity of the mixtures was significantly more than the chemical insecticides alone in the 7 days posttreatment test samples except for the Actellic 50EC and Vectobac 12AS mixture. In all the trials, with or without B.t.i, there was no significant difference in adult mortality, indicating that this B.t.i formulation, Vectobac 12AS, was not antagonistic to the adulticidal activity of the chemical insecticides. From this study, it can be concluded that chemical insecticides can be used effectively for both adult and larval control, but the chemical insecticides do not exhibit residual larvicidal activity. Hence, for an effective control of both Aedes larvae and adults, it is advisable to add B.t.i. to the chemical insecticides, as B.t.i is specifically larvicidal and is also able to effect extended residual larvicidal activity.
Increased scientific interest has led to the rise in biotechnological uses of halophilic and halotolerant microbes for hypersaline wastewater bioremediation. Hence, this study performed molecular docking, molecular dynamic (MD) simulations, and validation by Molecular Mechanic Poisson-Boltzmann Surface Area (MM-PBSA) calculations on the DehH2 from Bacillus thuringiensis H2. We aimed to identify the interactions of DehH2 with substrates haloacids, haloacetates, and chlorpyrifos under extreme salinity (35% NaCl). MD simulations revealed that DehH2 preferentially degraded haloacids and haloacetates (-6.3 to -4.7 kcal/mol) by forming three or four hydrogen bonds to the catalytic triad, Asp125, Arg201, and Lys202. Conversely, chlorpyrifos was the least preferred substrate in both MD simulations and MM-PBSA calculations. MD simulation results ranked the DehH2-L-2CP complex (RMSD □0.125-0.23 nm) as the most stable while the least was the DehH2-chlorpyrifos complex (RMSD 0.32 nm; RMSF 0.0 - 0.29). The order of stability was as follows: DehH2-L-2CP > DehH2-MCA > DehH2-D-2CP > DehH2-3CP > DehH2-2,2-DCP > DehH2-2,3-DCP > DehH2-TCA > DehH2-chlorpyrifos. The MM-PBSA calculations further affirmed the DehH2-L-2CP complex's highest stability with the lowest binding energy of -45.14 kcal/mol, followed closely by DehH2-MCA (-41.21 kcal/mol), DehH2-D-2CP (-31.59 kcal/mol), DehH2-3CP (-30.75 kcal/mol), DehH2-2,2- DCP (-29.72 kcal/mol), DehH2-2,3-DCP (-22.20 kcal/mol) and DehH2-TCA (-18.46 kcal/mol). The positive binding energy of the DehH2-chlorpyrifos complex (+180.57 kcal/mol) proved the enzyme's non-preference for the substrate. The results ultimately illustrated the unique specificity of the DehH2 to degrade the above-said pollutants under a hypersaline condition.Communicated by Ramaswamy H. Sarma.
To evaluate the effectiveness and residual effects of trypsin modulating oostatic factor-Bacillus thuringiensis israeliensis (TMOF-Bti) formulations against Aedes aegypti (Ae. aegypti) (L.) larvae at UKM Campus Kuala Lumpur.
An experiment was conducted to evaluate the use of Bacillus thuringiensis (Bt) as a probiotic to enhance the cellular innate immune response of the African catfish (Clarias gariepinus) challenged with a bacterial fish pathogen, Aeromonas hydrophila.
VectoBac DT, a tablet formulation of Bacillus thuringiensis israelensis (Bti) was evaluated for the potential control of dengue vectors in various types of potable water containers. On introduction to containers, the tablet sinks to the bottom and the Bti toxins are found concentrated at the sides and the base, while the treated water column is free of Bti toxins within 24 hours after tablet introduction. In a simulated study, earthen, HDPE and plastic containers were kept covered and laboratory-bred larvae were introduced to determine the control by the tablet. The efficacy and persistence of the tablet, with a control of > 90%, was significantly longer in earthen containers in comparison to the HDPE and plastic containers. Efficacy and persistence were observed in earthen containers for a minimum period of 5.5 months (166 days) both without water replenishment and with weekly, 50% water volume, replenishment, and for a maximum period of 2.2 months (66 days) with daily, 50% water volume, replenishment. In plastic and HDPE containers, the tablet activity had a persistence of 2.1 months (63 days) without water replenishment and 1.8 months (54 days) with weekly water replenishment. The efficacy and persistence of the VectoBac DT was significantly longer in the earthen containers, with or without regularly treated water exchange, due to the Bti toxins being embedded in the porous earthen container surfaces, which protects them from rapid degradation. Lesser toxin amounts are removed from the water column during water exchange. The efficacy of VectoBac DT was also evaluated for the control of natural infestation of Aedes larvae which were resistant to temephos at the WHO diagnostic dosage of 0.012 mg/l. The tablet significantly reduced the pupal density by 8 fold in earthen containers for 67 days and 5 fold in HDPE containers for 55 days in comparison to untreated containers (p < 0.05). However, the tablet was effective for a shorter period of 25 days post-tablet-introduction due to fungal infestation in the treated plastic containers. There is a need to determine the capacity of the VectoBac DT to reduce the dengue vector population to a threshold which will prevent dengue outbreaks in dengue endemic areas.
The presence of two cry-like genes first identified in Clostridium bifermentans subsp. malaysia CH18 was investigated in Clostridium species including 12 subspecies of Clostridium bifermentans, 13 strains of other members of Clostridia genus, and 13 different subspecies of Bacillus thuringiensis. Oligonucleotides designed to amplify the two toxin genes, cmb71 and cmb72, were used. We found that these genes are present in 80% of the Clostridium bifermentans strains tested and in 8% of the other Clostridium and Bacillus thuringiensis strains.
Comparative laboratory bioassays of three formulations of Bacillus thuringiensis H-14 (IPS-78, San 402-I and Bactimos) were conducted against late 3rd/early 4th instar larvae of four species of mosquito, viz., Aedes aegypti, Culex quinquefasciatus, Anopheles balabacensis and Mansonia (Mansonioides) indiana, in Malaysia. From the average response of the mosquito larvae to the three formulations of B. thuringiensis H-14, Ae. aegypti was found to be most susceptible, followed by Cx. quinquefasciatus, An. balabacensis and M. (M.) indiana in decreasing order. The LC50 values for Ae. aegypti, Cx. quinquefasciatus, An. balabacensis and M. (M.) indiana after a 48-hour exposure to IPS-78 formulation were 50.9, 129.3, 117.8 and 169.6 International Toxic Unit (ITU) Ae. ae./l; to San 402-I formulation were 54.6, 223.1, 405.1 and 177.6 ITU Ae. ae/l and to Bactimos formulation were 57.2, 175.7, 35.6 and 514.5 ITU Ae. ae./l respectively. The efficacy of the bacterial product was also found to be determined by its formulation in relation to the feeding and resting habits of the mosquito larvae. No delayed pupation or emergence was observed on the larvae exposed to B. thuringiensis H-14 at sub-lethal concentrations.
Thirteen strains among 3 species of entomopathogenic bacteria were tested against 3 medically important mosquito species in French Polynesia. Two strains of Bacillus thuringiensis were highly toxic to Aedes polynesiensis, Aedes aegypti, and Culex quinquefasciatus. Six of 7 strains of Bacillus sphaericus tested were highly toxic to Cx. quinquefasciatus but not to the Aedes spp. Clostridium bifermentans serovar. malaysia was more toxic to Ae. polynesiensis than to the other 2 species. Entomopathogenic bacteria merit field testing for larval mosquito control in French Polynesia.
A novel Bacillus thuringiensis strain highly toxic to mosquitoes was isolated from soil samples in Malaysia. This strain was shown to display a new subfraction of the H-28 flagellar antigen determining a new serovar H28a28c, which was designated serovar jegathesan. Bioassays indicated that Culex quinquefasciatus larvae are the most susceptible to this new isolate, whereas toxicity to Anopheles maculatus and Aedes aegypti larvae was 10 times lower. The potency of this new serotype is also comparable to most of the Malaysian B. thuringiensis H-14 isolates.
Studies were carried out on the bioefficacy and residual activity of Bacillus thuringiensis israelensis H-14 (Bti) (water-dispersible granules of VectoBac ABG 6511 and liquid formulations of VectoBac 12AS) and pyriproxyfen (insect growth regulator, Sumilarv 0.5%) as direct applications for control of larvae of Aedes aegypti and Aedes albopictus. Two dosages of each Bti formulation (285 and 570 international toxic units [ITU]/liter) and the integration of both Bti formulations and pyriproxyfen were used for residual tests with 45-liter earthen jars for a period of 4 wk. In 1 test series, the treated water was replenished daily with 6 liters of seasoned untreated water. In the 2nd test series, the water in the jars was topped up to the 40-liter level during evaluation. Neither Bti formulation remained effective for a full week. Water-dispersible Bti granules provided effective initial control activity against Ae. aegypti and Ae. albopictus for both test designs (with replenishment and without replenishment of water). The higher dosage (570 ITU/liter) for both Bti formulations was only partially effective at the end of 1 wk after being diluted. After 1 wk, water-dispersible Bti granules provided greater larval mortality than did liquid Bti formulation against both mosquito species when integrated with pyriproxyfen. Pyriproxyfen (79.5 and 159 mg/liter) on its own showed low larvicidal activity but provided very effective control of adult emergence. In this study, integration of Bti (285 and 570 ITU/liter) with pyriproxyfen (79.5 mg/liter) extended the duration of partial larval control somewhat, but live larvae persisted throughout the 4-wk test. The integration effect was more obvious when water-dispersible Bti granules were integrated with pyriproxyfen than when liquid Bti was used. Integration of Bti with pyriproxyfen had a negative effect on adult emergence, which was completely inhibited by pyriproxyfen after day 1. Daily replenishment of water increased Bti activity and provided slightly better larval control. Aedes albopictus and Ae. aegypti were both completely susceptible to the higher concentration of Bti and pyriproxyfen in both test designs (with replenishment and without replenishment of water).
Studies were carried out on the residual efficacy of Bacillus thuringiensis H-14 (water dispersible granule, VectoBac ABG 6511) as direct application in the control of Aedes larvae in the field. Field Aedes sp populations in the earthen and glass jars were predetermined before initiation of the trial. On confirmation of the presence of Aedes species in the designated area, Sungai Nibong Kecil, Penang Island, Malaysia, Bti was introduced in the 55L earthen and 3L glass jars). Two test designs were carried out. The first design had treated water replenished daily with 6L of seasoned water and the second design is without the replenishment of water but evaporated water was replenished. Bti was effective in the field for at least 35 days with more than 80% reduction in the Aedes larvae in the treated containers. For earthen jars with daily replenishment of water, 100% reduction was recorded for the first 3 days, while more than 80% reduction was recorded up to day 40. At day 60, Bti still provided an efficacy of 54.32 +/- 4.61 (%) of reduction. Whilst for earthen jars without daily replenishment of water, 100% reduction was recorded for the first 5 days, while more than 80% of reduction was recorded up to day 40. For the glass jars studied, similar efficacy was observed. In jars with daily replenishment of water a better larval control was observed. Percentage of reduction from day 50 to 60 for replenishment of water was between 50 to 70% compared to without replenishment of water with less than 40%.
Laboratory efficacy and residual activity of a water dispersible granule formulation of Bacillus thuringiensis israelensis (Bti) at the dosages of 3000, 6000 and 15000 ITU/L were conducted in this study. The study was conducted in two different size containers, earthen jar (45 L) and glass jar (3 L) with or without daily replenishment of 6 L and 0.3 L of water in the earthen and glass jars, respectively. Results indicate that for both earthen jar and glass jar evaluations, Bti at the tested dosages, performed effectively against Aedes aegypti, giving a minimum of 42 days effective killing activity. When the dosage was increased from 3000 ITU/L to 6000 ITU/L or 15000 ITU/L, the effective periods of the Bti increased by an additional one to three weeks. The Bti water dispersible granule provided better larvicidal activity with replenishment of water compared with non-replenishment of water especially for the higher dosage (15000 ITU/L).
The efficacy of three formulations of Bacillus thuringiensis var. israelensis was studied against Aedes albopictus in discarded tires. The formulations were: Vectobac G (corn cob formulation), Vectobac 12AS (aqueous suspension), and Bactimos WP (wettable powder formulation). Both Vectobac G and Vectobac 12AS were effective for 24 hr with more than 80% mortality. Both Vectobac formulations were significantly more effective than Bactimos WP for 24 hr after treatment (P < 0.0005). A week after treatment, Vectobac 12AS was significantly different than Bactimos WP (P < 0.05). However, Vectobac G did not differ significantly from Bactimos WP (P > 0.05); two weeks after spraying there was no significant difference among the various formulations (P > 0.05).