Bottom-Up Effects of Various Plant Growth Promoting Treatments on Fitness Parameters of Hippodamia variegata.

Abstract

Plant growth-promoting activities using biological, chemical, and organic fertilizers are well-documented for pest insects, their impacts on predators are less commonly studied. This research investigates whether bell pepper plants treated with plant growth-promoting rhizobacteria (PGPRs), arbuscular mycorrhizal fungi (AMF), vermicompost (30%), and zinc sulfate either separately or in selected combinations affect the nutrient indices and population growth traits of the ladybug predator, Hippodamia variegata (Goeze), when fed on aphids, Myzus persicae (Sulzer). Bell pepper plants were individually treated with two PGPRs (Bacillus subtilis and Pseudomonas fluorescens), one AMF (Glomus intraradices), soil amended with 30% vermicompost (v/v), and foliar application of zinc sulfate under greenhouse conditions. Combined treatments of AMF × B. subtilis and AMF × P. fluorescens were also tested. Nutritional indices and population growth parameters of predator were reared on the treated plants infested with aphids. Results showed that the efficiency of conversion of ingested food (ECI) in predator larvae was highest on B. subtilis-treated aphids and lowest on vermicompost-treated aphids. The relative growth rate (RGR) of predator was the highest on zinc sulfate-treated aphids and lowest on vermicompost-treated aphids. Predators fed on vermicompost-treated aphids had the lowest net reproductive rate (R₀) and intrinsic rate of increase (r), while R₀ was highest for predators fed on B. subtilis-treated aphids and r was highest on P. fluorescens- and B. subtilis-treated aphids. These findings suggest that zinc sulfate and biological fertilizers involving PGPRs can enhance the ecological fitness of predators and could be effective in biocontrol-based integrated pest management of aphids.