Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Abstract Only
Publication Acceptance Date: 1/10/2014
Publication Date: 2/10/2014
Citation: Portilla, M., Snodgrass, G.L., Luttrell, R.G. 2014. Effects of morning and night application of Beauveria bassiana strains NI8 and GHA against the tarnished plant bug in cotton. National Cotton Council Beltwide Cotton Conference. Belwide Cotton conference, January 5-8, 2014, New Orleans, LA. pp.729-734.
Interpretive Summary: The survival of conidia deposited on substrates exposed to direct solar radiation is highly affected, but the mortality obtained by contact mainly in the second day after spray indicated that spores also can be protected from UV-radiation within the canopy suggesting that the period of time that TPB feed or exist on the canopy could be long enough to get infected. This investigation showed that the rapid inactivation of B. bassiana spores by solar radiation could be considered a major impediment to the success of the control of the TPB; nevertheless, the NI8 strain represents a valuable resource to be utilized within an IPM framework, and it will significantly contribute to reduction in chemical pesticide use.
Technical Abstract: The tarnished plant bug, (TPB), Lygus lineolaris (Palisot de Beauvois), (Hemiptera: Miridae) an important pest of cotton (Gosssypium hirsutum L.) found in the Mississippi Delta is naturally attacked by the entomopathogenic fungus Beauveria bassiana (Balsamo) Vueillemin. In this study, two isolates of B. bassiana including the commercial strain GHA and the Mississippi Delta native NI8 strain were evaluated in the field for pathogenicity and infectivity against TPB. Effects of application times and solar radiation on mortality and sporulation were evaluated. In order to evaluate pathogenicity by direct spray, two-d old TPB adults from a laboratory colony were placed in cages located on the top part of cotton plants in the field prior to spraying B. bassiana strains with a multi-sprayer tractor calibrated to deliver 6.5 x 1012 spores/acre. Detailed observations were made on the effect of solar radiation by releasing 2-d old TPB adults in cages with sprayed branches of cotton plants cut 0, 1, and 2 days after morning and night applications. Differences on mortality and sporulation on TPB exposed to sprayed cotton branched for 24 hours were significant among treatments. Mortality and sporulation drastically decreased from 1.7-fold by the next day to 5.6-fold by the second day after B. bassiana NI8 night application and a reduction of 1.5-fold by the next day to 8.2-fold by the second day in morning application. Less than 10% sporulation was found two days after B. bassiana application for both strains. Overall, these results indicated that B. bassiana application resulted in decreased survival of TPB regardless of the isolates by direct spray or by contact. However, the superior performance of the Delta native strain NI8 was observed in all treatments applications and times of evaluation. An important obstacle to the efficacy of each isolates is their inability to survive exposure to solar radiation, which affects the use of this entomopathogenic fungus for the control of the TPB. However, the >50% mortality of TPB adults obtained by direct spray or by contact should make this fungi an attractive alternative for TPB control.