Side Effects of Three Recommended Insecticides Against Wheat Pests on Population of Natural Enemies Active in Wheat Fields of Ardabil, Tehran, and Golestan Provinces, Iran

Abstract

Background and Objectives

Wheat is a critical crop in Iran and pivotal in food security, economic stability, and political landscapes. Wheat fields are the habitat of many insects, including both beneficial and pest species. Therefore, various insecticides are employed in wheat fields to safeguard crop yields. However, pursuing pest control often entails unintended consequences for non-target organisms, particularly pollinators and natural enemies. This study aimed to evaluate the effect of both chemical and herbal insecticides on non-target insect populations within Iranian wheat fields. Although plant-derived insecticides may offer ecological benefits, the study emphasizes the need to evaluate their efficacy against pests and their impact on beneficial insects. Therefore, it is necessary to consider the possible effects of herbal and chemical insecticides on natural enemies.

Materials and Methods

This study evaluated the adverse effects of some recommended insecticides for wheat pests on some natural enemies. A completely randomized block design with five treatments and four replicates was employed. The experiment was conducted in Ardabil, Tehran, and Golestan, Iran. The size of each plot was 100m2 (10 x10), with a distance of 2m between blocks and plots. A total of 30 wheat stalks were randomly selected for sampling in each plot, and all larvae on these stalks were counted within the wheat field. Sampling was performed on four occasions: one day before and 3, 7, and 14 days after spraying. The treatments included matrine (at concentrations of 1.5 and 2ml/L), deltamethrin (0.3ml/L), fenitrothion (1ml/L), and a control treatment (water). The potential effects of the insecticides were examined on the larvae of natural enemies, including the seven-spotted ladybird, flower fly, and green lacewing. Tehran and Ardabil provinces had low flower fly and green lacewing populations across all treatments, including control. However, the ladybird population was sufficient for evaluation. Therefore, the effects of the insecticides on ladybirds were investigated in these provinces.

Results

The reduction in the population of seven-spotted ladybirds in Ardabil caused by the insecticides was insignificant on days 3 and 7 and significant on day 14. Deltamethrin caused the most negative effect on days 3 and 7, while matrine 2ml/L had the most negative effect on day 14. Deltamethrin consistently caused the largest ladybird population decline in Tehran, with a significant difference from other treatments on all days except day 3. Fenitrothion exhibited the least adverse effect throughout the experiment. Golestan had the healthiest natural enemy populations. In this province, a suitable population of seven-spotted ladybirds, flower flies, and green lacewings was observed. The study confirmed insecticide-induced declines in these populations, with deltamethrin causing the most significant reductions for ladybirds and flower flies, while fenitrothion had the least impact. All insecticides severely reduced green lacewing populations. Based on the results of the 7th day, the reduction of the population of seven-spotted ladybirds in different provinces caused by matrine 1.5 and 2ml/L, fenitrothion, and deltamethrin was 31.04% – 57.91%, 54.19% – 77.58%, 25.01% – 70.16% and 72.02% – 89.35%, respectively. In addition, population reduction caused by matrine 1.5 and 2 ml/L, fenitrothion, and deltamethrin was 31.61%, 67.01%, 24.58%, and 79.06% for flower fly, and 73.24%, 82.79%, 73.24% and 95.94% for green lacewing, respectively. In all cases, the reduction caused by matrine 2ml/L was higher than matrine 1.5ml/L. On day 7, most insecticides were slightly harmful to seven-spotted ladybirds in all provinces except Tehran and Golestan, where fenitrothion was harmless and deltamartin moderately harmful. On this day, matrine, fenitrothion, and deltamethrin were slightly harmful, harmless, and moderately harmful to flower flies, respectively. Moreover, matrine 1.5ml/L and fenitrothion were slightly harmful to green lacewing, while matrine 2ml/L and deltamethrin were moderately harmful.

Discussion

Deltamethrin consistently exhibited the most pronounced adverse effects across all treatments and natural enemy populations, while fenitrothion had the least severe impact. Green lacewing populations displayed the highest insecticide sensitivity among the studied natural enemies. Based on the results, the effect of insecticides on non-target beneficial organisms was essential when developing integrated pest management (IPM) strategies. Avoiding the application of insecticides, particularly deltamethrin, during peak natural enemy populations was crucial to minimize unintended ecological consequences and promote a balanced ecosystem within wheat fields.