Quantification of pH tolerance levels among entomopathogenic nematodes

Area of Science:

• Agricultural Science
• Environmental Science
• Microbiology

Background:

• Soil pH critically influences nutrient availability, plant development, and soil microbial communities.
• Entomopathogenic nematodes (EPN) are beneficial soil microorganisms and natural parasites of insects, offering an alternative to chemical insecticides.
• Understanding EPN tolerance to environmental factors like soil pH is crucial for their effective application in biological control.

Purpose of the Study:

• To investigate the pH tolerance of 11 steinernematid and 6 heterorhabditid entomopathogenic nematode species.
• To determine the survival rates of EPN populations when exposed to a range of pH levels (pH 2 to pH 11).
• To identify EPN species suitable for deployment in soils with varying pH conditions.

Main Methods:

• EPN populations were exposed to pH levels from 2 to 11, prepared using ammonium-acetate and citrate-phosphate buffer solutions.
• Survival rates of infective juvenile EPNs were assessed after exposure to different pH conditions.
• Comparative analysis of survival data between different EPN species and families (Steinernematidae and Heterorhabditidae) was performed.

Main Results:

• Highest infective juvenile survival for most EPN populations occurred between pH 3 and pH 10 in citrate-phosphate solutions, with over 50% survival.
• Steinernema carpocapsae populations exhibited greater than 90% survival from pH 3 to pH 11 in citrate-phosphate solutions.
• Steinernematids generally showed higher survival in ammonium-acetate solutions compared to heterorhabditids, with S. carpocapsae and S. riobrave demonstrating broad pH tolerance.

Conclusions:

• Certain entomopathogenic nematode species, particularly Steinernema carpocapsae and Steinernema riobrave, possess significant tolerance to both acidic and alkaline soil pH levels.
• These findings support the selection of specific EPN strains for biological control strategies in soils with extreme pH conditions.
• The differential pH tolerance among EPN species highlights the importance of species-specific selection for optimizing biological pest control efficacy.