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Beauveria bassiana (Bal.-Criv.) is an important entomopathogenic fungus being used for the management of various agricultural pests worldwide. However, all strains of B. bassiana may not be effective against whitefly, Bemisia tabaci, or other pests, and strains show diversity in their growth, sporulation, virulence features, and overall bioefficacy. Thus, to select the most effective strain, a comprehensive way needs to be devised. We studied the diversity among the 102 strains of B. bassiana isolated from 19 insect species based on their physiological features, virulence, and molecular phylogeny, to identify promising ones for the management of B. tabaci. Strains showed diversity in mycelial growth, conidial production, and their virulence against B. tabaci nymphs. The highest nymphal mortality (2nd and 3rd instar) was recorded with MTCC-4511 (95.1%), MTCC-6289 (93.8%), and MTCC-4565 (89.9%) at a concentration of 1 × 106 conidia ml−1 under polyhouse conditions. The highest bioefficacy index (BI) was in MTCC-4511 (78.3%), MTCC-4565 (68.2%), and MTCC-4543 (62.1%). MTCC-4511, MTCC-4565, and MTCC-4543 clustered with positive loading of eigenvalues for the first two principal components and the cluster analysis also corresponded well with PCA (principal component analysis) (nymphal mortality and BI). The molecular phylogeny could not draw any distinct relationship between physiological features, the virulence of B. bassiana strains with the host and location. The BI, PCA, and square Euclidean distance cluster were found the most useful tools for selecting potential entomopathogenic strains. The selected strains could be utilized for the management of the B. tabaci nymphal population in the field through the development of effective formulations. Key points: • 102 B. bassiana strains showed diversity in growth and virulence against B. tabaci. • Bioefficacy index, PCA, and SED group are efficient tools for selecting potential strains. • MTCC-4511, 4565, and 4543 chosen as the most virulent strains to kill whitefly nymphs. [ABSTRACT FROM AUTHOR]

Whitefly Bemisia tabaci (Gennadius) is an important pest of cotton in India. The study of taxonomic diversity and its distribution on cotton is lacking. Such studies are necessary to identify the genetic groups of B. tabaci and its distribution on cotton in India. The proper identification of genetic groups and their distribution, which, ultimately, can lead to the timely development and utilization of management practices. The current study was undertaken to explore the genetic diversity and phylogeographic structure of B. tabaci from all the three major cotton growing zones representing different agro-climatic conditions of India. 290 partial mitochondrial Cytochrome Oxidase I (mt COI) sequences of whitefly population of six major cotton-growing states covering 22 districts were used in the analysis. Phylogenetic analysis revealed the presence of two monophyletic clades, Asia I and Asia II1 genetic groups represents South-Central India and North India respectively. Asia II1 is found more predominately distributed in the cotton leaf curl virus (CLCuV) disease-prone north Indian cotton-growing states. Higher genetic divergence (16.8–19.2%) was observed between the populations of Asia I and Asia II1 genetic group. Genetic differentiation analysis confirmed the phylogeographic structure of B. tabaci as isolated by distance. Our results in mapping the distribution of genetic groups in cotton ecosystems paved the way for the further studies and formulation of area-wide management practices for cotton whitely in India. [ABSTRACT FROM AUTHOR]

[Display omitted] • EPF varied in mycelial growth, sporulation, nymphal mortality of Bemisia tabaci. • New record of Fusarium verticillioides infection on Bemisia tabaci. • Bioefficacy index considered mycelial growth, sporulation, nymphal mortality by EPF. • BI proved as an effective predictor for selecting EPF for field efficacy. • MT-4511, IT-10499 showed higher efficacy against B. tabaci nymphs than insecticides. • These could be utilized as eco-friendly management of whitefly and CLCuD in cotton. The whitefly , Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae), is becoming a serious problem on Bt cotton. It causes enormous crop loss through its direct feeding and as a vector of cotton leaf curl virus. Chemical-dependent management is harming the environment and increased insecticide resistance is often observed in the fields. Identification of most virulent strains of entomopathogenic fungi (EPF) is essential to serve as an important component of an IPM program for management of B. tabaci. Compared to B. tabaci adults, the nymphal stage is reported to be more susceptible to entomopathogens, and targeting nymphs also helps vector management. We evaluated the bioefficacy of EPF and chemical pesticides against nymphs of B. tabaci on Bt cotton under polyhouse and field conditions. The bioefficacy index (BI) was considered as a mechanism to select the most effective EPF strains for field evaluation. The highest nymphal mortality under polyhouse conditions was recorded for Metarhizium anisopliae NA-01299 (86.7%), Beauveria bassiana MT-4511 (85.1%), Cordyceps javanica IT-10498 (81.1%), IT-10499 (81%), and B. bassiana NA-0409 (78.2%) relative to other EPF strains, spiromesifen (69.6%), buprofezin (62.2%) and pyriproxyfen (52.7%) at 7-days-post-spray treatment (DAS). However, among all the EPF, the highest BI was recorded in C. javanica IT-10499 (77%), IT-10495 (75.4%), Fusarium verticillioides IT-10493 (74.6%), and B. bassiana MT-4511 (73.1%). The pooled data of two-year field trials (2017–18 & 2018–19) revealed that the highest nymphal mortality was recorded for MT-4511 (85%), IT-10499 (83.2%), and pyriproxyfen 10% EC (78.6%) at 7-DAS. The BI-based selection of EPF proved to be a useful predictor of field efficacy. A sequential spray of the selected EPF would be a vital approach for resilient and sustainable integrated management of the B. tabaci nymphal population under field conditions. [ABSTRACT FROM AUTHOR]