title: Time-concentration-mortality modeling of the synergistic interaction of Beauveria bassiana and imidacloprid against Nilaparvata lugens.
abstract: Interactions between the entomopathogenic fungus, Beauveria bassiana SG8702, and imidacloprid on Nilaparvata lugens (Homoptera: Delphacidae) were studied in laboratory bioassays by spraying suspensions of unformulated conidia (assay 1) and aqueous dilutions of emulsifiable conidia formulation alone (assay 2) or together with imidacloprid at the sub-lethal rates of 0.5, 1.0 and 2.0 microg ml(-1) (assays 3-5). Each assay consisted of five conidia concentrations plus an appropriate control and three replicates, each including 30-40 third-instar nymphs, so as to generate time-concentration-mortality data for modeling analysis. A mineral oil-based emulsion used to formulate B bassiana slightly enhanced fungal activity but had no significant impact on the background mortality of N lugens. On the basis of LC50 estimates and associated variances on days 4-12 after spraying, synergistic interactions of both agents or formulations were determined by estimating relative potencies of assay 2 over assay 1 (1.2-9.0), assay 3 over assay 2 (1.3-1.7), assay 4 over assay 2 (7.5-9.6), assay 5 over assay 2 (22.7-101), assay 4 over assay 3 (3.8-5.8), assay 5 over assay 3 (16.1-61.0), and assay 5 over assay 4 (3.0-10.5). The time-concentration-mortality modeling method was not only mathematically but also biologically robust to evaluate the interactions of B bassiana and imidacloprid on N lugens. Compared with their counterparts, enhanced fungal formulations displayed consistently earlier or greater activities against the pest species based on LC50 and LT50 estimates determined from their time-concentration-mortality relationships. The results highlight a potential for pest control by combined formulation or application of B bassiana and imidacloprid.
authors.affiliation: Institute of Microbiology, College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang 310029, China. mgfeng@zju.edu.cn
authors.forename: Ming-Guang
authors.initials: MG
authors.lastname: Feng
authors.forename: Xiao-Ying
authors.initials: XY
authors.lastname: Pu
mesh_terms: D000818:Animals; D001203:Ascomycota; D006430:Hemiptera; D007093:Imidazoles; D007300:Insect Control / Q000379:methods*; D007306:Insecticides; D015233:Models, Statistical; D000073943:Neonicotinoids; D009574:Nitro Compounds; D010572:Pest Control, Biological / Q000379:methods*; D013997:Time Factors
chemical_list: D007093:Imidazoles; D007306:Insecticides; D000073943:Neonicotinoids; D009574:Nitro Compounds; C082359:imidacloprid