Efficacy and efficiency of new Bacillus thuringiensis var israelensis and Bacillus sphaericus formulations against Afrotropical anophelines in Western Kenya

We evaluated the efficacy of new water-dispersible granular (WDG) formulations of Bacillus thuringienis var. israelensis (Bti; VectoBac) and B. sphaericus (Bs; VectoLex), Valent BioScience Corp., Illinois, USA) for the control of larval Anopheles gambiae sensu lato Giles mosquitoes in a malaria-endemic area around Lake Victoria, Western Kenya. WDG and powder formulations were compared in laboratory bioassays and followed by efficiency and residual effect assessments of both WDG formulations in open field experiments. LC50 and LC95 values for the Bti/Bs strains and their formulations show high susceptibility of A. gambiae sensu stricto under laboratory conditions. The larvae proved more susceptible to Bs than to Bti and the WDG formulations were slightly superior to the powder formulations. High efficiency was also shown in the open field trials, and a minimum dosage of 200 g/ha Bti WDG, representing the LC95 of the laboratory tests, was sufficient to fully suppress emergence of mosquitoes when applied at weekly intervals. Bti WDG did not show a residual effect, irrespective of the concentration applied. The Bs WDG formulation, however, showed significant larval reductions up to 11 days post-treatment at application doses of either 1 or 5 kg/ha. We conclude that the main malaria vector in our study area is highly susceptible to these microbial control agents. Minimum effective dosages to achieve elimination of the larval population in a given habitat are extremely low and environmental impact is negligible. Microbial products for larval control have therefore great potential within Integrated Vector Management programmes and may augment control efforts against adult vector stages, such as the use of insecticide-treated bednets, in many parts of Africa.     

Toxicity of Bacillus thuringiensis var. Israelensis to Chironomids in Pond Mesocosms

A pond mesocosm study was conducted in a central Minnesota wetland to evaluate the potential toxicity of the microbially-derived insecticide Bacillus thuringiensis var. israelensis (B.t.i.) to chironomids. B.t.i. was applied as VectoBac® G to mesocosms on two occasions (21 d apart) at five rates (0.3X, 1X, 2.5X, 5X, 10X) with three replicate mesocosms per rate. The 1X rate (9 kg/ha) was that operationally used by the Minneapolis-St. Paul Metropolitan Mosquito Control District for early summer mosquito control. Chironomid abundances following B.t.i. treatment were compared to abundances in untreated control mesocosms. The abundance of Chironomidae larvae was significantly reduced at the 10X treatment 4 d after the first B.t.i. application. Chironomid abundance was also reduced after the second application with 10X, but showed strong signs of recovery within 32 d. Chironominae, the numerically dominant subfamily within the Chironomidae, showed a similar response. The abundance of Orthocladiinae larvae was significantly reduced at both the 10X and 5X treatments, whereas the Tanypodinae appeared unaffected by all B.t.i. treatments. Of the two tribes comprising the Chironominae, the Chironomini displayed a response very similar to that of its parent subfamily, although reductions in abundance were not statistically significant. The tribe was dominated by Dicrotendipes, Einfeldia, and Endochironomus, none of which were significantly reduced following either 10X application. The second tribe, the Tanytarsini, were slightly more susceptible to B.t.i. than the Chironomini, displaying significant reductions in abundance after both 10X applications. The Tanytarsini were dominated by Paratanytarsus, which were reduced by 91% 4 d after both 10X B.t.i. applications. Tanytarsini and Chironomini were also reduced in abundance (by 83 and 75%, respectively) at the 5X treatment, but reductions were not statistically significant. Regressions of larval chironomid abundance versus B.t.i. treatment rate indicated that the B.t.i. rates required to reduce chironomid abundance by 25, 50, and 75% were 1.5–2.0X, 2.1–3.3X, and 3.5–11.0X, respectively. Emergence of adult Chironomidae was significantly reduced at the 10X B.t.i. treatment, but not at 5X. The same trend was observed for the Chironominae, which comprised 82% of the family, but not for Orthocladiinae and Tanypodinae. Emergence of Ceratopogonidae and Chaoboridae was unaffected by all B.t.i. treatments.     

Suppression of exposure to malaria vectors by an order of magnitude using microbial larvicides in rural Kenya

OBJECTIVE: To determine the contribution larviciding could make to reduce the burden of malaria, by conducting a trial of microbial larvicides in a 4.5 km2 area in and around a large village in rural western Kenya. METHOD: The abundance of immature and adult mosquitoes was monitored for 12 months under baseline conditions. Then microbial larval control was implemented for 28 months. After the intervention, the abundance of immature and adult mosquitoes was monitored for a further 12 months. RESULTS: Of the 419 mosquito larval habitats identified, 336 (80%) originated from human activities. Application of Bacillus thuringiensis var. israelensis and Bacillus sphaericus larvicides reduced the proportion of aquatic habitats containing Anopheles larvae from 51% during non-intervention periods to 7% during the intervention. The occurrence of late instar Anopheles in habitats was reduced from 39% and 33% in pre-intervention and post-intervention periods to 0.6% during intervention. Overall, larviciding reduced Anopheles larval density by 95% and human exposure to bites from adults by 92%. The estimated cost of providing this protection to the human population in the study area was less than US$ 0.90/person/year. CONCLUSION: Appropriately applied microbial larvicides can substantially and cost-effectively reduce human exposure to malaria in rural sub-Saharan Africa.     

苏云金杆菌对斯氏按蚊Hor株幼虫杀伤效果的分析

目的检测苏云金杆菌以色列亚种(Bti)对斯氏按蚊Hor株四龄幼虫的杀灭效果及作用特点,为合理使用Bti进行蚊虫防治提供参考标准和理论依据。方法首先采用Probit analysis生物测定的方法研究Bti剂量与斯氏按蚊幼虫累计死亡率的关系,通过线性回归分析获得相关公式,计算半致死浓度(LC50)等重要参数,探讨Bti对斯氏按蚊的杀伤效果。然后利用半致死浓度的Bti处理不同密度的斯氏按蚊幼虫,分析按蚊幼虫密度对Bti杀伤效果的影响。结果Bti对斯氏按蚊四龄幼虫的累计死亡率随作用时间和浓度的升高而增大,Bti的浓度对数值与累计死亡率P值呈较好的线性关系,根据所获得的公式计算出Bti作用12、24、48和72h后,半数致死浓度(LC50)分别为(1242±60)IU/L、(1112±45)IU/L、(1010±73)IU/L、(855±32)IU/L,95%致死浓度(LC95)分别为(4 170±138)IU/L、(3746±444)IU/L、(3462±409)IU/L、(3080±464)IU/L。而且随着幼虫密度的增加,其累计死亡率显著降低。结论 Bti株对斯氏按蚊四龄幼虫具有较好的杀伤效果,作用强、起效快,是一种较为理想的的灭蚊生物制剂;在Bti的使用剂量的确定上,应充分考虑蚊虫密度的因素,蚊虫密度越大所需Bti剂量应适当加大。     

Spotted Fever Group Rickettsioses in Israel, 2010–2019

In a multicenter, nationwide, retrospective study of patients hospitalized with spotted fever group rickettsiosis in Israel during 2010–2019, we identified 42 cases, of which 36 were autochthonous. The most prevalent species was the Rickettsia conorii Israeli tick typhus strain (n = 33, 79%); infection with this species necessitated intensive care for 52% of patients and was associated with a 30% fatality rate. A history of tick bite was rare, found for only 5% of patients; eschar was found in 12%; and leukocytosis was more common than leukopenia. Most (72%) patients resided along the Mediterranean shoreline. For 3 patients, a new Rickettsia variant was identified and had been acquired in eastern, mountainous parts of Israel. One patient had prolonged fever before admission and clinical signs resembling tickborne lymphadenopathy. Our findings suggest that a broad range of Rickettsia species cause spotted fever group rickettsiosis in Israel.     

苏云金杆菌CryIVD转基因工程藻不同贮存时间对淡色库蚊不同龄期幼虫的杀灭效果

目的观察苏云金杆菌CryIVD转基因贮存藻对不同龄期淡色库蚊幼虫的杀灭效果。方法大量培养工程藻,干燥后保存,应用不同时间的贮存藻作用于不同龄期淡色库蚊幼虫。结果干燥贮存的工程藻数年后仍有较高的杀蚊毒效,尽管杀蚊毒效较新鲜工程藻有所下降,但在105个/ml数量级不同龄期的幼虫仍有50%以上死亡。对不同龄期淡色库蚊幼虫杀灭效果比较表明,1~3年贮存藻3组比较,在106个/ml数量级浓度的蚊幼虫死亡率差异无统计学意义（F=9.32,P〉0.01）,而贮存1年组和3年组在105个/ml数量级浓度及以下,死亡率差异有统计学意义（F=101.21,P〈0.01）。结论转基因蓝藻在干燥贮存情况下仍能保持毒蛋白的稳定遗传和杀幼虫作用,为今后的现场应用提供更方便的选择。     

苏云金杆菌以色列变种对伊蚊库蚊和按蚊幼虫毒效的实验观察

目的 目的 研究苏云金杆菌以色列变种 （Bti） 可湿性粉剂对伊蚊、 库蚊和按蚊幼虫的毒杀效果。方法 方法 采用生物测定 法, 测定Bti可湿性粉剂对白纹伊蚊幼虫、 淡色库蚊幼虫和中华按蚊幼虫的毒杀效果, 计算半数致死浓度 （LC50 ）。结果 结果 Bti 可湿性粉剂对Ⅲ龄白纹伊蚊幼虫、 淡色库蚊幼虫和中华按蚊幼虫的LC50 分别为0.104、 0.160 μg/ml和0.324 μg/ml, 效价 分别为0.125、 0.192 IU/ml和0.389 IU/ml; 连续接触中华按蚊Ⅲ龄幼虫 1、 2 d和 3 d的LC50分别为0.324、 0.092 μg/ml和0.032 μg/ml, 效价分别为0.389、 0.110 IU/ml和0.038 IU/ml; 对中华按蚊Ⅰ、 Ⅱ、 Ⅲ龄和Ⅳ龄幼虫的LC50分别为0.024、 0.137、 0.324 μg/ml和0.450 μg/ml, 效价分别为0.029、 0.164、 0.389 IU/ml和0.540 IU/ml。结论 结论 Bti对3种蚊虫幼虫均有较好的毒杀效 果, 但对伊蚊和库蚊幼虫效果更好, 且幼虫虫龄越小, 毒杀效果越好。     

微生物杀虫剂Vectobac G200和C_3-41乳剂杀灭淡色库蚊幼虫的现场效果

两种微生物制剂现场防制淡色库蚊幼虫的效果表明,Vectobac G200颗粒剂按0.5g/m~2、C_3-41乳剂按1ml/m~2施药,可有效地控制淡色库蚊幼虫的孳生,持效均为3天。增加施药剂量可明显增加持效期。上述两种微生物杀虫剂3g/m~2或3ml/m~2在污水中可分别持效7～9天和13天。     

苏云金杆菌cryIVD基因的表达及杀蚊毒效测定

目的研究苏云金杆菌(B.t.i)cryIVD基因用于蚊虫生物防治.方法经IPTG诱导,重组质粒在大肠埃希菌DH5α中进行表达,并进行十二烷基硫酸钠-聚丙烯酰胺凝胶电泳(SDS-PAGE)及免疫印迹(Western-blot)分析,观察其杀蚊毒效.结果经SDS-PAGE及Western-blot分析显示,特异蛋白带的分子质量单位为72 ku,并且该蛋白对蚊虫具有杀灭作用.结论在大肠埃希菌中B.t.i cryIVD基因单独表达,并具有杀蚊活性.     

苏云金杆菌以色列亚种晶体蛋白CryIVD基因的克隆及表达产物的效果测定

目的　　克隆、表达苏云金杆菌以色列亚种晶体蛋白CryIVD基因并测定其杀蚊毒效。　 方法　采用PCR技术 ,扩增得到CryIVD基因片段 ;通过双酶切及连接反应 ,将该基因克隆入大肠杆菌质粒 pUC18构建重组克隆及表达载体 ;转化E .coliDH5α,提取重组质粒进行酶切鉴定及DNA序列测定 ;以IPTG诱导表达CryIVD蛋白 ,SDS PAGE分析表达产物并进行杀蚊毒效测定。　结果　CryIVD基因成功克隆并在宿主菌中正确表达 ,表达产物对蚊幼的杀灭毒效测定显示其对淡色库蚊Ⅱ～Ⅲ龄健康幼虫的LC50 为 2 .3 8× 10 6 cells ml,对白纹伊蚊健康幼虫的LC50 为 1.6× 10 7cells ml。　结论　CryIVD基因被成功克隆和表达 ,且其表达产物有明显杀蚊幼活性。