Morphological and molecular identification of four Purpureocillium isolates and evaluating their efficacy against the sweet potato whitefly, Bemisia tabaci (Genn.) (Hemiptera: Aleyrodidae)

Background Entomopathogenic fungi are widely distributed and well described within the fungal kingdom. This study reports the isolation, characterization, and virulence of 4 Purpureocillium lilacinum isolates against the sweet potato whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae). Results Four strains of Purpureocillium lilacinum (XI-1, XI-4, XI-5, and J27) were isolated from soil samples from different localities of China. The morphological studies observed that four strains showed essentially the same morphological characteristics. After 7 days of cultivation, the colonies were purple, round, and bulged. Conidia were single-celled, oval to spindle-shaped, chain-like, and the spore size was about 2.0–2.3 × 3.1–4.0 μm. The genome-based identification results showed that ITS sequences of XI-1 (GenBank accession # MW386433), XI-4 (GenBank accession # MW386434), XI-5 (GenBank accession # MW386435), and J27 (GenBank accession # MW386436) were similar to another P. lilacinum. The newly identified strains of P. lilacinum proved pathogenicity to B. tabaci under laboratory conditions. In addition, the P. lilacinum isolate XI-5 was the most virulent one against different nymphal instars of whitefly having median lethal concentration (LC50) values of 4.99 × 106, 4.82 × 105, and 2.85 × 106 conidia/ml, respectively, 7 days post application. Conclusion The newly isolated strains of P. lilacinum can be developed as a potential biopesticide against the whitefly although extensive field bioassays as well as development of proper formulation are still required.

Effects of Mulch Type, Plant Cultivar, and Insecticide Use on Sweet Potato Whitefly Population in Chili Pepper

One of the most devastating pests of chili pepper is the sweet potato whitefly (SPW), Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae). It sucks plant sap, emits honeydew on which sooty mold fungi grow, and transmits the pepper yellow leaf curl Indonesia virus (PepYLCIV), the most damaging viral disease of chili in Indonesia. Farmers rely mainly on insecticide to control the insect with two to three sprays in a week. To reduce the insecticide use, an integrated approach needs to be developed. Therefore, the current study evaluated the effectiveness of the integration of reflective mulch, host plant resistance, and insecticide use for managing the sweet potato whitefly on the chili pepper. In 2018, a complete randomized block design was used in three separate trials to assess the effects of mulch, cultivar, or insecticide application frequency on the numbers of whitefly eggs, nymphs, and adults. In 2019, a split-split plot design was used to evaluate the effects of the integration of mulch, cultivar, and insecticide application frequency on the numbers of whitefly eggs, nymphs, and adults. The results showed that the reflective silver mulch had significantly lower numbers of whitefly eggs, nymphs, and adults, in comparison to the rice straw mulch and bare ground treatments. Chili plants cv. Bara was more resistant than Bhaskara against B. tabaci in the field; however, in the no-choice trial, no significant difference was detected between both cultivars. Insecticide applications twice per week and once per week were equally effective in controlling the whitefly on the susceptible cultivar (Bhaskara). Overall, the integration of reflective mulch, resistant cultivar, and insecticide application every two weeks effectively suppressed B. tabaci populations on the chili pepper. This approach could substantially reduce the number of insecticide applications from twice per week (commonly practiced by chili farmers in the area) to one application only in two weeks.