Influence of some environmental conditions on stability and activity of Bacillus thuringiensis formulations against the cotton leaf worm, Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae)

Abstract

The entomopathogenic bacterium Bacillus thuringiensis (Bt) has been used in crop protection for the last 70 years; however, many environmental conditions affect its activity. The present study was directed to evaluate the influence of certain environmental conditions on stability and activity of Bt samples of the two commercial formulations (Dipel 2 × 6. 4% WP and Protecto 9.4% WP), when stored under accelerated hot storage, shelf, and outdoor storage. Photo degradation of the two formulations was studied in aqueous solution. The results revealed that the loss percentage of Protecto formulation was above the permissible limits of WHO specifications after 2 years of storage at ambient conditions and the thermal stability of the Bt was affected negatively depending on the storage periods. In accordance with this trend, the bioassay tests versus neonate and second instar larvae of the cotton leaf worm, Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae), showed a decrease in toxicity of the formulations to (60%) after storage at 35 ± 2°C for 12 weeks and about (70%) after storage under sunlight for 2 days. Photolysis of aqueous solutions reduced the half-life of formulations by about 1-2 days. The stability of Bt should be evaluated prior to submission for registration as these products have showed less stability under storage at ambient conditions. The stakeholders and decision-makers can utilize these results and examine such products case by case.

Viability and reconstitution of delta-endotoxins from Bacillus thuringiensis var. israelensis extracts after forty years of storage against Aedes aegypti (Diptera: Culicidae)

“…According to different studies, it is suggested that the larger the protein size, the longest it persists: Cry4 (130 kDa)> Cry11 (70 kDa)> Cyt (28 kDa) (Tetreau et al 2012 andBen 2014). In this study, it was clear that all Bti extracts tested had a high storage stability, in contrast with findings of different studies reporting poor protein stability of endotoxins under storage periods, in which shelf life was often low and the viability of products did not exceed 2 years under ambient conditions (Moustafa et al 2018).…”

“…All this can produce conformational changes in its structure (Hung et al 2016), thus hinder toxic activity. However, there are some reports highlighting UV light and sunlight as a primary degradation pathway (Hung et al 2016;Moustafa et al 2018). Further research is needed to understand the role that this disaccharide could have in moderately conserving the activity and viability of the larvicidal proteins.…”

“…Each one of the Bti proteins had demonstrated different patterns of persistence (Cry4>Cry11>Cyt) in the environment (Tetreau et al 2012). It is known that products based on natural molecules tend to be less stable than synthetic compounds; hence, shelf life of entomopathogen formulations is often low (Villaverde et al 2014;Moustafa et al 2018). Few studies have evaluated the persistence of the insecticidal activity of B. thuringiensis formulations under storage conditions, whereby the percentage loss of the formulated Bt products after a period of over 2 years (24%) was higher than the permissible limit (16%) demonstrating low shelf life (Moustafa et al 2018).…”

Monitoring Resistance and Biochemical Studies of Three Egyptian Field Strains of Spodoptera littoralis (Lepidoptera: Noctuidae) to Six Insecticides

“…However, modification of the target site could lead to insensitivity of insect pests to insecticides [ 55 ]. In addition, factors such as UV light, sunlight, photolysis in water and shelf life could affect the insecticide efficiency and delay the development of the resistance/prevent it from occurring [ 56 ]. Thus, we speculate that the inconsistency with other studies might be due to the different species of insect, type of insecticide, time of sampling or method of treatment.…”

The Effects of Ultraviolet B on The Efficacy of Bacillus thuringiensis var. kurstaki Formulations Against Tobacco Armyworm, Spodoptera litura (Lepidoptera: Noctuidae)

“…Thus, it is inexpensive and practically can be propagated by the farmers. Unfortunately, this bacterium is sensitive and easily degraded by climatic factors (Abbaszadeh et al 2011;Moustafa et al 2018;Van Bokhorst-van de Veen et al 2015), for example, by ultraviolet sunlight. Ultraviolet is the main cause of cry toxin degradations (Pan et al 2017).…”