Susceptibility of Tetranychus urticae Koch. (Acari: Tetranychidae) to Isolates of Entomopathogenic Fungus Beauveria bassiana

Abstract

Bioassays with five isolates of the entomopathogenic fungus Beauveria bassiana (Bals.- Criv.) Vuillemin were conducted under laboratory conditions with a goal to estimate their virulence to the two-spotted spider mite Tetranychus urticae Koch. (Acari: Tetranychidae). Common bean plants with mites were treated by spraying conidial suspensions of isolates at concentrations of 106, 107 and 108 conidia/ml. Lethal effects of the fungal isolates were evaluated as percentages of cumulative daily mortality due to mycoses, corrected for mortality in the control variant. Virulence of the isolates was estimated based on values of the median lethal time (LT50) calculated by probit analysis for the variants treated with conidial suspensions at the concentration of 106 conidia/ml. The two-spotted spider mite was found susceptible to the examined isolates of the entomopathogenic fungus B. bassiana. Mycosis caused to T. urticae by the B. bassiana isolates 444 Bb and 445 Bb had fast lethal effect after treatment with conidial suspensions even at the concentration of 106 conidia/ ml. The mean mortality values of host individuals were 83.78 ± 3.62% and 68.49 ± 4.28% on the first day, respectively, and up to 100% in both variants on the fourth day. The isolates 426 Bb, 444 Bb and 445 Bb of B. bassiana were highly virulent to two-spotted spider mites with values of the median lethal time varied within overlapped narrow confidence intervals from 0.122 to 1.084 days (average value 0.162 days), from 0.117 to 1.398 days (average value 0.146 days) and from 0.106 to 1.162 days (average value 0.131 days), respectively. Significant differences regarding virulence of the three isolates at p-level < 0.05 could not been proved. The other two examined isolates were distinctly less virulent to T. urticae than these three B. bassiana isolates.

Pet izolata entomopatogene gljive Beauveria bassiana (Bals.-Criv.) Vuillemin ispitivano je u biotestu pod laboratorijskim uslovima sa ciljem da se proceni njihova virulentnost za grinje- paučinare Tetranychus urticae Koch. (Acari: Tetranychidae). Biljke pasulja sa grinjama tretirane su rasprskavanjem suspenzija izolata u koncentracijama od 106, 107 i 108 konidija/ml. Letalno dejstvo izolata gljive ocenjivano je kao procenat kumulativne dnevne smrtnosti kao posledice mikoze, korigovan za smrtnost u kontroli. Virulentnost izolata je procenjivana na osnovu vrednosti srednjeg letalnog vremena (LT50) izračunatog probit analizom u varijantama sa suspenzijom konidija u koncentraciji od 106 konidija/ml. Grinje-paučinari su pokazale osetljivost na ispitivane izolate entomopatogene gljive B. bassiana. Mikoze koje su na T. urticae prouzrokovali izolati B. bassiana sa oznakom 444 Bb i 445 Bb pokazale su brzo letalno dejstvo nakon tretmana suspenzijama, čak i u koncentraciji od 106 konidija/ml. Srednje vrednosti smrtnosti grinja domaćina bile su respektivno 83,78 ± 3,62% i 68,49 ± 4,28% prvog dana, a četvrtog dana do 100% u obe varijante ogleda. Izolati B. bassiana sa oznakom 426 Bb, 444 Bb i 445 Bb bili su visokovirulentni za grinjepaučinare, a vrednosti srednjeg letalnog vremena varirale su uz preklapanje uskih intervala poverenja respektivno od 0,122 do 1,084 dana (prosečno 0,162 dana), od 0,117 do 1,398 dana (prosečno 0,146 dana) i od 0,106 do 1,162 dana (prosečno 0,131 dana). Nisu potvrđene značajne razlike u pogledu virulentnosti ova tri izolata na nivou p < 0,05. Manja virulentnost druga dva izolata za T. urticae bila je jasno izražena u odnosu na ova tri izolata B. bassiana.