Pre-Crop Chemical Control Has No Effects on Corn Leaf Aphid, Rhopalosiphum maidis (Fitch) (Hemiptera: Aphididae) Endosymbiotic Bacterial Diversity Along an Industrial Maize Management

TL;DR

This study found that pre-crop pesticide use does not affect the bacterial symbionts of corn leaf aphids in industrial maize fields.

Contribution

The study provides new evidence that pre-crop pesticide treatments have no significant impact on aphid endosymbiont diversity.

Findings

The primary symbiont Buchnera aphidicola was present in all aphid samples.

Facultative symbionts like Serratia symbiotica and Wolbachia spp. showed no significant variation due to pesticide use.

Pre-crop pesticide application had no measurable effect on aphid endosymbiotic bacterial diversity.

Abstract

In the present study, the endosymbiotic bacterial species diversity was assessed in a conventionally managed maize (Zea mays) field, that represents more than 90% of the Central European maize crops. Because no insecticide treatment is allowed legally in Europe to control corn leaf aphids (Rhopalosiphum maidis) in industrial maize crops, the only method is the assessment of the pre-crop treatment effects on corn leaf aphids endosymbionts that confers adaptation to host. This is also important because in the last five years, the corn leaf aphid population is increasing; therefore, alternative methods must be considered as no treatments before harvest are allowed in accordance with the European Green Deal. In our study, the primary symbionts Buchnera aphidicola as well as a few facultative species (Serratia symbiotica, Wolbachia spp.) dominate corn leaf aphid communities in all sites and between generations. No effect of pre-crop pesticide treatment on endosymbionts was detected.

During this research, the corn leaf aphids endosymbiotic bacterial diversity was tested in the same crop systems (monoculture industrial maize as grain for livestock) and the same soil type (Chernozem) when pre-crop pesticide management was used. Bacterial symbionts were analyzed using Illumina systems, and the Silva 16S NR99 V138.2 database was used to assign bacterial taxa on genus and species levels. The presence of the obligate endosymbiont B. aphidicola has been clearly detected in all cases, and in all samples but its abundance varied between samples inside crops, but not between crops and generations. The facultative symbionts S. symbiotica and Wolbachia spp. frequency varied between generations, and increased at generation II; however, differences were not significant. We concluded that the pre-crop pesticide application has no effect on corn leaf aphids bacterial symbionts, so the indirect pesticide application on aphids adaptation is low or nonexistent.

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