Thuringiensis Var Research Articles

A review of the potential impacts of coastal mosquito control programs on Australian Stingless Bees (Apidae, Meliponini)-likely exposure pathways and lessons learned from studies on honey bees.

The impact of the programmatic use of larvicides for mosquito control on native stingless bees (e.g., Apidae, Meliponini) is a growing concern in Australia due to heightened conservation awareness and the growth of hobbyist stingless bee keeping. In Australia, the two most widely used mosquito larvicides are the bacterium Bacillus thuringiensis var. israelensis (Bti) and the insect hormone mimic methoprene (as S-methoprene). Each has a unique mode of action that could present a risk to stingless bees and other pollinators. Herein, we review the potential impacts of these larvicides on native Australian bees and conclude that their influence is mitigated by their low recommended field rates, poor environmental persistence, and the seasonal and intermittent nature of mosquito control applications. Moreover, evidence suggests that stingless bees may display a high physiological tolerance to Bti similar to that observed in honey bees (Apis mellifera), whose interactions with B. thuringiensis-based biopesticides are widely reported. In summary, neither Bti or methoprene is likely to pose a significant risk to the health of stingless bees or their nests. However, current knowledge is limited by regulatory testing requirements that only require the use of honey bees as toxicological models. To bridge this gap, we suggest that regulatory testing is expanded to include stingless bees and other nontarget insects. This is imperative for improving our understanding of the potential risks that these and other pesticides may pose to native pollinator conservation.

Empowering rural communities for effective larval source management: A small-scale field evaluation of a community-led larviciding approach to control malaria in south-eastern Tanzania

IntroductionLarval source management, particularly larviciding, is mainly implemented in urban settings to control malaria and other mosquito-borne diseases. In Tanzania, the government has recently expanded larviciding to rural settings across the country, but implementation faces multiple challenges, notably inadequate resources and limited know-how by technical staff. This study evaluated the potential of training community members to identify, characterize and target larval habitats of Anopheles funestus mosquitoes, the dominant vector of malaria transmission in south-eastern Tanzania. MethodsA mixed-methods study was used. First, interviewer-administered questionnaires were employed to assess knowledge, awareness, and perceptions of community members towards larviciding (N = 300). Secondly community-based volunteers were trained to identify and characterize aquatic habitats of dominant malaria vector species, after which they treated the most productive habitats with a locally-manufactured formulation of the biolarvicide, Bacillus thuringiensis var. israelensis. Longitudinal surveys of mosquito adults and larvae were used to assess impacts of the community-led larviciding programme in two villages in rural south-eastern Tanzania. ResultsAt the beginning of the program, the majority of village residents were unaware of larviciding as a potential malaria prevention method, and about 20 % thought that larvicides could be harmful to the environment and other insects. The trained community volunteers identified and characterized 360 aquatic habitats, of which 45.6 % had Anopheles funestus, the dominant malaria vector in the area. The preferred larval habitats for An. funestus were deep and had either slow- or fast-moving waters. Application of biolarvicides reduced the abundance of adult An. funestus and Culex spp. species inside human houses in the same villages, by 46.3 % and 35.4 % respectively. Abundance of late-stage instar larvae of the same taxa was also reduced by 74 % and 42 %, respectively. ConclusionThis study demonstrates that training community members to identify, characterize, and target larval habitats of the dominant malaria vectors can be effective for larval source management in rural Tanzania. Community-led larviciding reduced the densities of adult and late-stage instar larvae of An. funestus and Culex spp. inside houses, suggesting that this approach may have potential for malaria control in rural settings. However, efforts are still needed to increase awareness of larviciding in the relevant communities.

INSECTICIDE SUSCEPTIBILITY IN TWO POPULATIONS OF Aedes aegypti L. (Diptera: Culicidae) FROM GUERRERO, MEXICO, AND RECOMMENDATIONS FOR THEIR MANAGEMENT

The Aedes aegypti L. mosquito is a vector of diseases such as classic and hemorrhagic dengue (DENV), chikungunya (CHIKV), Zika (ZIKV), yellow fever (YFV), and Mayaro (MAYV). In 2019 alone, in Latin America, there were 2.7 million cases and 1206 deaths. In Mexico, government programs for managing this pest include the elimination of larval habitats and chemical control of larvae and adults. The objective of this study was to evaluate the response of two larvae and adult populations of A. aegypti from the state of Guerrero, Mexico, under laboratory conditions, to insecticides with different modes of action and to make considerations for their management. In the bioassays, larvae showed susceptibility to permethrin, malathion, deltamethrin, and Bacillus thuringiensis var. israelensis; low resistance to Temephos and propoxur; as well as moderate resistance to Spinosad. Both adult populations showed resistance to permethrin and susceptibility to deltamethrin, while the Acapulco population showed resistance to alpha-cypermethrin. For larvae, Spinosad is suggested to be used in times of high incidence of dengue. During drought, it is advisable to include rotations of B. thuringiensis var. israelensis with organophosphates. For adults, the use of imidacloprid in combination with botanical insecticides is considered a rational alternative to rotations with organophosphates and pyrethroids.

Efficacy of Biopesticides and Insecticides against Lepidopteran Pests in Rainfed Castor

Field experiments were conducted during kharif 2022 to evaluate the bio-efficacy of biopesticides and insecticides against tobacco caterpillar, Spodoptera litura (F.);semilooper, Achaea janata L. and shoot and capsule borer, Conogethes punctiferalis Guenee on castor. The results revealed that, all the insecticide treatments were significantly superior over untreated control. The highest% reduction of lepidopteran pest complex over the control after three sprays was recorded with spinetoram 11.7 SC followed by cyantraniliprole 10.26 OD, Bacillus thuringiensis var. kurstaki (Btk) SC, profenophos 50 EC, lambda cyhalothrin 5 EC and B. thuringiensis var. kurstaki (Btk) WP 1.5, Beauveria bassiana SC and Neemazal 10000 PPM. Highest seed yield was recorded with spinetoram (1434 kg/ ha) followed by cyantraniliprole (1338 kg/ ha) as against 940 kg/ ha in untreated control. The maximum incremental cost-benefit ratio of 1:3.13 was obtained with application of spinetoram followed by lambda-cyhalothrin (1:3.00) and Btk SC (1:2.73).

Insights into the whole genome sequence of Bacillus thuringiensis NBAIR BtPl, a strain toxic to the melon fruit fly, Zeugodacus cucurbitae.

Bacillus thuringiensis is the most widely used biopesticide, targets a diversity of insect pests belonging to several orders. However, information regarding the B. thuringiensis strains and toxins targeting Zeugodacus cucurbitae is very limited. Therefore, in the present study, we isolated and identified five indigenous B. thuringiensisstrains toxic to larvae of Z. cucurbitae. However, of five strains NBAIR BtPl displayed the highest mortality (LC50 = 37.3μg/mL) than reference strain B. thuringiensis var. israelensis (4Q1) (LC50 = 45.41μg/mL). Therefore, the NBAIR BtPl was considered for whole genome sequencing to identify the cry genes present in it. Whole genome sequencing of our strain revealed genome size of 6.87Mb with 34.95% GC content. Homology search through the BLAST algorithm revealed that NBAIR BtPl is 99.8% similar to B. thuringiensis serovar tolworthi, and gene prediction through Prokka revealed 7406 genes, 7168 proteins, 5 rRNAs, and 66 tRNAs. BtToxin_Digger analysis of NBAIR BtPl genome revealed four cry gene families: cry1, cry2, cry8Aa1, and cry70Aa1. When tested for the presence of these four cry genes in other indigenous strains, results showed that cry70Aa1 was absent. Thus, the study provided a basis for predicting cry70Aa1 be the possible reason for toxicity. In this study apart from novel genes, we also identified other virulent genes encoding zwittermicin, chitinase, fengycin, and bacillibactin. Thus, the current study aids in predicting potential toxin-encoding genes responsible for toxicity to Z. cucurbitae and thus paves the way for the development of B. thuringiensis-based formulations and transgenic crops for management of dipteran pests.

Exploring selected bioinsecticides for management of cotton aphids (Aphis gossypii Glover) of brinjal in Bangladesh

Brinjal (Solanum melongena L.) is a popular vegetable in Bangladesh being nutritious, tasty, and cultivable throughout the year. Insect pests are the major constraint to its successful cultivation and production. The present study was conducted during the winter season when the sucking insect pests especially cotton aphids (Aphis gossypii Glover) are most abundant. Aphid infestation was observed in the brinjal plants since the early vegetative stage and sometimes the infestation rate reached up to 100 percent. Moreover, the infestation rate fluctuated with plants or duration. Aphids suck the cell saps resulting in stunting the growth of plants and yield reduction. As brinjal is consumed without peeling, contamination with toxic insecticides is a health concern. To address this, some bioinsecticides including abamectin preparation ‘Biomax M’, sodium lauryl ether sulphate preparation ‘Fizimite’, azadirachtin preparation ‘Fytomax’, Saccharopolyspora spinosa and Bacillus thuringiensis var. Kurstaki broth mixture preparation ‘Spinomax’, and potassium salt of fatty acid preparation ‘Fytoclean’ were selected to combat aphids. Besides, Voliam Flexi was applied as chemical control. A field study showed that abamectin preparation Biomax M was very potent against aphids showing zero percent aphid infestation. In addition, the chemical control Voliam Flexi 300 SC also provided zero percent aphid infestation. Therefore, Biomax M might be the non-toxic alternative to Voliam Flexi 300 SC for controlling aphids.

Trophic effects of Bti-based mosquito control on two top predators in floodplain pond mesocosms

Chironomid (Diptera: Chironomidae) larvae play a key role in aquatic food webs as prey for predators like amphibian and dragonfly larvae. This trophic link may be disrupted by anthropogenic stressors such as Bacillus thuringiensis var. israelensis (Bti), a biocide widely used in mosquito control. In a companion study, we recorded a 41% reduction of non-target larval chironomids abundance in outdoor floodplain pond mesocosms (FPMs) treated with Bti. Therefore, we examined the diet of two top predators in the FPMs, larvae of the palmate newt (Salamandridae: Lissotriton helveticus) and dragonfly (Aeshnidae: predominantly Anax imperator), using bulk stable isotope analyses of carbon and nitrogen. Additionally, we determined neutral lipid fatty acids in newt larvae to assess diet-related effects on their physiological condition. We did not find any effects of Bti on the diet proportions of newt larvae and no significant effects on the fatty acid content. We observed a trend in Aeshnidae larvae from Bti-FPMs consuming a higher proportion of large prey (Aeshnidae, newt, damselfly larvae; ~42%), and similar parts of smaller prey (chironomid, mayfly, Libellulidae, and zooplankton), compared to controls. Our findings may suggest bottom-up effects of Bti on aquatic predators but should be further evaluated, for instance, by using compound-specific stable isotope analyses of fatty acids or metabarcoding approaches.

Encapsulation of Bacillus thuringiensis using sodium alginate and chitosan coacervates for insect-pest management

The study investigates the complex coacervation process of sodium alginate (SA) and chitosan (CS), aiming to optimize the yield of coacervates formed from these marine polysaccharides. Structural interactions between SA and CS were analyzed across varying chitosan concentrations (0.01 mg to 20 mg/mL) using turbidimetric analysis. The optimal chitosan concentration for maximum coacervate formation was determined to be 10 mg/mL. Under these conditions, Bacillus thuringiensis var. kurstaki (Bt) strain Bt-127 was successfully microencapsulated, achieving an entrapment rate of 56 %. Boric acid was selected as the cross-linking agent due to its compatibility with Bt and the SA-CS coacervates. Microscopic analysis confirmed the formation of coacervates/microcapsules and effective entrapment of Bt within them, with an entrapment efficiency of 98 %. Fourier transform infrared spectroscopy verified the chemical interactions between SA and CS within the coacervates. Bioassays against Spodoptera litura larvae using the leaf dip method demonstrated the efficacy of the encapsulated Bt formulation, showing an LC50 of 0.51 g/L. These findings highlight the potential of SA-CS coacervates for effective Bt microencapsulation and application in pest control.

Residual toxicity of pesticide active substance commonly used in tomato crop on the predator Nesidiocoris tenuis (Heteroptera: Miridae)

AbstractNesidiocoris tenuis (Reuter) (Heteroptera Miridae) is a key biological control agent of the tomato leaf miner Tuta absoluta (Meyrick). However, in cases of prey scarcity, this predator switches into a phytophagous pest causing ring injuries in stems of tomato plants. The aim of this study was to assess the side effects of dry residues and explore the presence of target site resistance mutations of 10 insecticides, two bioinsecticides, an acaricide and a fungicide widely applied in IPM, on adults of N. tenuis collected from two different regions of Crete; the Western and the Eastern side of the island during two successive years. Lethal toxicity trials were performed on sprayed tomato stems and toxicity of adults of N. tenuis was recorded 2 h, 7 and 14 days after exposure. At both populations, chlorpyrifos, acetamiprid and thiamethoxam were moderately harmful at the application day and slightly harmful 7 days after the application. Only chlorpyrifos maintained its toxicity for more than 7 days. All the rest tested pesticides (emamectin benzoate, abamectin, chlorantraniliprole+abamectin, chlorantraniliprole, deltamethrin, tebufenpyrad, spinosad, Bacillus thuringiensis var kurstaki, metaflumizone and myclobutanil) were classified as harmless. Additionally, analysis of insecticide target site sequences indicated the absence of resistance mutations in both populations. Overall, our findings illustrate the impact of 15 pesticides and their residual toxicity on the mortality rates of N. tenuis adults.

Field Efficacy of Selected Chemicals and Biopesticides against Brinjal Shoot and Fruit Borer (Leucinodes orbonalis) on Brinjal (Solanum melongena) at Prayagraj

A field experiment was carried out at the Central research farm of Sam Higginbottom University of Agriculture, Technology, and Sciences, located in Prayagraj, Uttar Pradesh, during the kharif 2023-24. The experiment was designed following a randomized block design with three replications. It encompassed eight treatments: T1 - Neem oil 3%@ 30ml/lit, T2 - Metarhizium anisopliae @ 2.5ml/lit,T3 - Bacillus thuringiensis var. kurstaki @ 2gm/lit, T4 - Spinosad 45 SC @ 0.3 ml/lit, T5 - Emamectin benzoate @ 0.4 gm/lit, T6 - Chlorpyrifos 20 EC @ 2.5ml/lit, T7 - Chlorantraniliprole 18.5 SC @ 0.4ml/lit and T8 - untreated control. The objective was to assess the field efficacy of selected chemicals and biopesticides against Leucinodes orbonalis (Guenee) infestation on brinjal in Prayagraj. Two rounds of spraying was conducted at 15-days interval. Data on shoot and fruit infestation was recorded after each spraying and picking, including the percentage of shoot infestation. The results showed that the initial population of the pest before the spray exhibited a non-significant distribution. Following the spray, the findings demonstrated that T5 – Emamectin benzoate @ 0.4 gm/lit exhibited significant effectiveness against shoot and fruit borer, comparable to T7 – Chlorantraniliprole 18.5 SC, at 3, 7, and 14 days post-spraying. Following closely in efficacy were Spinosad 45 SC and Chlorpyrifos 20 EC. The highest cost benefit ratio was recorded- T5-Emamectin benzoate, followed by T7-Chlorantraniliprole 18.5 SC. The highest cost-benefit ratio was recorded in T5– Emamectin benzoate @ 0.4gm/lit followed by T7- Chlorantraniliprole 18.5 SC @ 0.4ml/lit and the lowest monetary return was observed with the control (T0).

Effects of chironomid larvae density and mosquito biocide on methane and carbon dioxide dynamics in freshwater sediments.

Small lentic water bodies are important emitters of methane (CH4) and carbon dioxide (CO2), but the processes regulating their dynamics and susceptibility to human-induced stressors are not fully understood. Bioturbation by chironomid larvae has been proposed as a potentially important factor controlling the dynamics of both gases in aquatic sediments. Chironomid abundance can be affected by the application of biocides for mosquito control, such as Bti (Bacillus thuringiensis var. israelensis). Previous research has attributed increases in CH4 and CO2 emissions after Bti application to reduced bioturbation by chironomids. In this study, we separately tested the effect of chironomid bioturbation and Bti addition on CH4 production and emission from natural sediments. In a set of 15 microcosms, we compared CH4 and CO2 emission and production rates with high and low densities of chironomid larvae at the bioturbating stage, and standard and five times (5x) standard Bti dose, with control sediments that contained neither chironomid larvae nor Bti. Regardless of larvae density, chironomid larvae did not affect CH4 nor CO2 emission and production of the sediment, although both rates were more variable in the treatments with organisms. 5xBti dosage, however, led to a more than three-fold increase in CH4 and CO2 production rates, likely stimulated by bioavailable dissolved carbon in the Bti excipient and priming effects. Our results suggest weak effects of bioturbating chironomid larvae on the CH4 and CO2 dynamics in aquatic ecosystems. Furthermore, our results point out towards potential functional implications of Bti for carbon cycling beyond those mediated by changes in the macroinvertebrate community.

Fruit pests of plum plantations of the Right-Bank Forest-Steppe of Ukraine and efficiency of protection

Goal. To determine the technical effectiveness of pesticides of different origin against fruit-damaging pests of plum in the conditions of the Right-Bank Forest-Steppe of Ukraine.
 Methods. Field, field-laboratory. The species composition of plum fruit pests was studied during systematic surveys in plum plantations of the L.P. Symyrenko Experimental Station of Pomology of the Institute of Horticulture of NAAS during 2021—2023. Accounting was carried out according to generally accepted methods. The research scheme included 8 variants. Yield and marketability were recorded during harvesting. The technical efficiency of Mospilan, RP (acetamiprid, 200 g/kg), Proclaim, 5 SG, v.g. (emamectin benzoate, 50 g/ kg) and Bitoxibacillin-BTU®r (bacteria Bacillus thuringiensis var. Thuringiensis, 1 ml of the drug contains 3 billion cells and 0.5% — 0.7% exotoxin) was determined at different consumption rates.
 Results. In the Right-Bank Forest-Steppe of Ukraine, the species composition of plum fruit pests is represented by black plum trach (Hoplocampa minuta Christ.), plum moth (Grapholitha funebrana Tr.) and thick-skinned weevil (Eurytoma schreineri Schr.). The most numerous and harmful species in 2021—2022 was the black plum borer, and in 2023 — the plum moth.
 Conclusions. Mospilan RP, Proclaim, 5 SG, v.g. and Bitoxibacillin-BTU® in plum plantations provided a decrease in the number of fruit-damaging pests, which made it possible to obtain higher-grade products. The technical efficiency was: for plum trach — 78.5—88.5%, plum moth — 81.0—85.0, and the weevil — 73.0—79.0%. During the years of research, all preparations showed the lowest effectiveness against plum borer.

Efficacy of Chromafenozide Insecticide to Control Tirathaba rufivena and Its Impacts on Oil Palm Pollinator E. kamerunicus

Newly marketed insecticide known with active ingredient Chromafenozide claimed to be potent against various lepidopterous insects, but at the same time almost non-toxic to non-lepidopterous species, including pollinators, predators and parasitoids. This trial aim to evaluate the effectiveness of Chromafenozide insecticides to control population of Tirathaba rufivena in oil palm planted on peat soil and its impact on pollinator weevil, Elaedobius kamerunicus. The trial was divided into two parts which are field assessment of insecticides efficacy and laboratory assay to know the direct effect of insecticide application on E. kamerunicus. Besides Chromafenozide, insecticides used in this trial Cypermethrin and Bacillus thuringiensis var kurstaky as comparison. The results of efficacy test showed that Tirathaba infestation decreased significantly in the Cypermethrin, B. thuringiensis, and Chromafenozide treatments compared to control. However, among these treatments did not show a significant difference. Nevertheless, each of the tested insecticide caused significantly mortality to E. kamerunicus. E. kamerunicus mortality rate of each insecticide treatment showed that Chromafenozide was less detrimental as compared Cypermethrin, but significantly detrimental to B. thuringiensis. B. thuringiensis was not significantly different compared to control.

Insecticide resistance level of Aedes aegypti L. (Diptera: Culicidae) in northern Mexico

Objective: To determine the response of the larvae of three Ae. aegypti populations from the Mexican North Pacific region to insecticides with different mode of action.
 Design/Methodology/Approach: Three colonies were obtained placing ovitramps in peridomestic sites in Guadalajara (Jalisco), Culiacan (Sinaloa), and La Paz (Baja California Sur). Based on the methodology proposed by WHO, the bioassays were carried out with F1 larvae in the early fourth instar.
 Results: The larvae from the three field colonies had high resistance to permethrin and low resistance to deltamethrin; however, they were susceptible to Spinosad and Bacillus thuringiensis var. Israelensis. The Culiacan strain showed a high resistance to the malathion and propoxur insecticides.
 Study Limitations/Implications: The results provided valuable information about the response of these populations to insecticides, which are useful to establish resistance in the lab. Consequently, further studies should be carried out to complement the information obtained in these field tests.
 Findings/Conclusions: The data indicated resistance levels to pyrethroid insecticides (mainly permethrin), as well as to organophosphates and carbamates.

Management of Fruit and Shoot Borer, Leucinodes orbonalis (Guenee) in Brinjal through Sequential Application of Selected Insecticides and Biorationals

Leucinodes orbonalis Guenee (Lepidoptera: Crambidae), commonly known as brinjal shoot and fruit borer is a dreaded pest in India. The bio efficacy of insecticides and biorationals has been test verified in managing fruit and shoot borer through logical sequential schedules. The results of the present field experiment conducted during Summer 2023 in Agricultural and Horticultural research Station (AHRS), Bavikere revealed the most effective insecticidal schedule among the tested sequences. The sequence containing Chlorantraniliprole 18.5 SC @ 0.3 ml/L - Spinosad 45 SC @ 0.4 ml/L - Lufenuron 5 EC @ 1.0 ml/L - Bacillus thuringiensis var. kurstaki @ 2.0 g/L demonstrated remarkable success in reducing the damage caused by L. orbonalis along with economic viability and high cost-benefit ratio.

Phylogeny of a Mosquitocidal Bacillus thuringiensis var israelensis

Objectives: The study aims to compare the 16srRNA sequence of Bacillus thuringiensis var israelensis available in the National Center for Biotechnology Information, database, the sequence length, the relatedness, identity, and ancestral property by constructing a phylogenetic tree and by basic local alignment tool. Methods: The 16srRNA sequence of all the Bacillus thuringiensis var israelensis was retrieved from the database. A basic local alignment tool was used to study the description of the sequences, the percent identity, graphical summary, and alignment. Mega software was used to draw the phylogenetic tree. Results: The total number of mosquitocidal 16srRNA gene sequences was 19. One sequence VCRC-B17 strain was the complete genomic sequence deposited other 18 hits were partial sequences. The Expected value, percent identity, maximum, and total score of 18 hits shows a significant match with the query sequence VCRC-B17. The graphic summary result displays that the 18 hits align with the query sequence as they are coded with the highest score coding color bar, red with a ≥ 200 alignment score. The phylogenetic tree did not support the monophyletic status indicating there is a diversity in the strain. Conclusion: The 19 sequences deposited in the database are identified as a mosquito larvicidal Bacillus thuringiensis var israelensis based on the alignment score or match even though they do not possess an equal base pair length with the query sequence.

Physical and bio-control methodologies for integrated management of buffalo fly-Haematobia exigua (Diptera: Muscidae)

Haematobia exigua, the buffalo fly, is a common ectoparasite of buffaloes and cattle in India causing economic losses and underlines the necessity of effective control strategies against them. The present study was planned to evaluate larvicidal activity of few methods for physical and biological control for integarated management of Haematobia exigua flies. Out of four bacterial bio-control agents evaluated by in-vitro assay and Probit analysis, two bacteria i. e. Bacillus thuringiensis var israelensis and Bacillus thuringiensis var kurstaki showed excellent larvicidal activity against H. exigua with LC50 value of 134 and 135 mg per liter of water respectively. Whereas, other two bacteria i. e. Bacillus weihenstephanensis WSBC and KBAB4 failed to show desired larvicidal activity. It can be concluded that B ti and B tk have future as effective bacterial agents (BCAs) in the control and integrated management of buffalo and horn fly. An experiment was conducted in the laboratory and on field for judging the efficacy of a physical method of tightly covering dung pats with polythene sheet for control of larvae of H. exigua. The laboratory result showed only 14.73% larvae were survived and developed per 100 gm of the faeces in the pot covered with polythene sheet as against significantly higher number 78.33% in the control group. During field trial, average larval count from dung pits before the experiment was 86.33 per 250 gm of faeces and it has been significantly reduced to 11.80 after covered with polythene sheets for two weeks. It indicated that physical method of covering the dung pits works immensely and thus can be inducted in IPM program as one of the effective physical control alternatives.

Larvicidal effect of Spinosad and Bacillus thuringiensis var. israelensis on Aedes aegypti (Linnaeus, 1762) (Diptera: Culicidae)

The use of biological larvicide based on Bacillus thuringiensis var. israelensis (Bti) has stood out for its effectiveness in controlling mosquito Aedes aegypti. The larvicide Spinosad is used in the National Dengue Control Program. This study evaluated the effect of Spinosad and Bti larvicide at various temperatures in a laboratory environment. The assays were performed with 10 larvae in quintuplicate, at temperatures of 18° C, 25° C and 32° C, with 24-hour monitoring. The larvae exposed to Bti were eliminated within 0.5 hours at ambient and hot temperatures (32° C), while at colder conditions (18° C) it took 1.5 hours for complete elimination. Regarding Spinosad, 50% survived for 11 hours, but all larvae were killed after 24 hours. The results reinforce the indication of these products for larval control of the species under the conditions of temperature fluctuation.

Morphological Features of Mosquito Larvicidal Bacillus Thuringiensis Isolated From Soil Samples of Nepal

Anopheles, Culex, and Aedes spp are the main vectors for transmitting malaria, Japanese encephalitis, lymphatics filariasis, dengue, zika, chikungunya, etc. Mosquito-borne diseases are increasing especially dengue in Nepal. Additional tools are required to decrease the disease rate. Biological control tools like Gambusia fish, Cyclopods, Bacillus thuringiensis, etc., have not been adopted and are unavailable in Nepal. The research aims to isolate mosquitocidal Bacillus thuringiensis a biological control tool from the soil samples of Nepal. Bacillus thuringiensis (Bt) was isolated from the soil samples of Nepal by the acetate selection method. The larvicidal bioassay of Bt was studied against the field-collected mosquito larvae. The isolate showing larvicidal activity was coded as Bacillus thuringiensis -14P2A (Bt-14P2A). The growth pattern of the positive control strain Bacillus thuringiensis var israelensis (Bti-IPS-82) and the test strain were studied in different types of culture media. The microscopic morphology was studied by using different staining techniques. Bt-14P2A and Bti -IPS-82 caused 100% mortality of field-collected larvae. Both the strains showed the same type of colony morphology in a standard culture media and uniform turbidity with sedimentation type of growth pattern in broth media. The strains were Gram-positive single rod-shaped of size 1.2X4.8µm in both negatively stained slides and Gram-stained slides. A slight difference in the endospore location was terminal in Bti-IPS-82 and subterminal in Bt-14P2A. The newly isolated Bt-14P2A differs from Bti-IPS-82 in arrangement and endospore location but harbors the same morphological characteristic and larvicidal activity as the positive control strain.

Bio-Efficacy of Novel Insecticides and Biopesticides against Diamondback Moth, Plutella xylostella (Linn.)

The present investigation entitled ‘bio-efficacy of Novel insecticides and bio-pesticides against Diamondback moth, Plutella xylostella (Linn.) was carried out on the cabbage, variety ‘Golden Acre’ during Rabi, 2021-22 and 2022-23. At Crop Research Centre, Sardar Vallabhbhai Patel University of Agriculture and Technology, Meerut (UP). The data were recorded on five randomly selected plants once in a standard week. Pooled data of both the year (2021 and 2022), After treatments, spinosad 2.50% SC at 600 ml ha-1 consistently showed the lowest larval count on days 3, 7, and 14, with 3.33, 2.17, 2.25 larvae per five plants followed by emamectin benzoate 5% SG at 200 g ha-1, diafenthiuron 50% WP at 600g ha-1, Bacillus thuringiensis var. kurstaki at 1000 g ha-1, Beauveria bassiana at 1500 ml ha-1 and Metarhizium anisopiliae at 2000 g ha-1, and nimbecidine 0.03% at 2500 ml-ha, respectively. The nimbecidine 0.03% at 2500 ml ha-1 recorded the lowest efficacy. Chemical and biological treatments varied significantly, while chemicals had similar efficacy, and biologicals were equally effective. Control plots had the highest larvae count.