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

Moataz A. M. Moustafa,Mohammed A. Saleh,Mohamed A. Kandil,Izat R. Ateya

doi:10.1186/s41938-018-0064-x

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.

Highlights

Bacillus thuringiensis (Bt) is one of the earliest developed entomopathogens and widely used as biopesticide
Radiation from sunlight or ultra violet (UV) light is the main limitation that obviously reduced the potency of Bt crystals against different insect pests (Dunkle and Shasha 1988; Ignoffo 1992; Khorramvatan et al 2014)
Insect rearing and bioassays Insect source Spodoptera littoralis larvae were obtained from the laboratory of pesticide, Cairo University, Egypt, that reared under a complete absence of insecticides (Eldefrawi et al 1964)

Summary

Introduction

Bacillus thuringiensis (Bt) is one of the earliest developed entomopathogens and widely used as biopesticide. It produces insecticidal proteins (δ-endotoxins) which exhibit toxicity to many insect species belong to order Lepidoptera, Diptera, and Coleoptera. As it is known that products based on natural molecules tend to be less stable than synthetic compounds, their residual effects are biodegradable (Gupta and Dikshit 2010; Villaverde et al 2014). These products are not stable under natural environmental stresses such as temperature, ultra violet (UV) radiation, and sunlight. Radiation from sunlight or UV light is the main limitation that obviously reduced the potency of Bt crystals against different insect pests (Dunkle and Shasha 1988; Ignoffo 1992; Khorramvatan et al 2014)

Methods

Results

Conclusion