Tri-Trophic Impacts of Bt-Transgenic Maize on Parasitoid Size and Fluctuating Asymmetry in Native vs. Novel Host-Parasitoid Interactions in East Africa.

Josephine Songa,Dennis Ndolo,Gábor Lövei

doi:10.3390/insects9020038

Josephine Songa, Dennis Ndolo + Show 1 more

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https://doi.org/10.3390/insects9020038

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Abstract

Environmental stress can affect trait size and cause an increase in the fluctuating asymmetry (FA) of bilateral morphological traits in many animals. For insect parasitoids, feeding of hosts on transgenic maize, expressing a Bacillus thuringiensis toxin gene is a potential environmental stressor. We compared the size of antennae, forewings, and tibia, as well as their FA values, in two parasitoids developed on two East African host species feeding on non-transgenic vs. transgenic maize. The two lepidopteran stem-borer hosts were the native Sesamia calamistis Hampson (Lepidoptera: Noctuidae) and a recent invader, Chilo partellus Swinhoe (Lepidoptera: Crambidae). The two braconid parasitoids were the native, gregarious larval endoparasitoid Cotesia sesamiae and the recently introduced Cotesia flavipes. Both parasitoids attacked both hosts, creating evolutionarily old vs. novel interactions. Transient feeding of hosts on transgenic maize had various effects on FA, depending on trait as well as the host and parasitoid species. These effects were usually stronger in evolutionarily novel host–parasitoid associations than in the older, native ones. These parameters have capacity to more sensitively indicate the effects of potential stressors and merit further consideration.

Highlights

The use of genetic transformation technology in crops allowed several crop plants to express genes that encode insecticidal proteins from the bacterium Bacillus thuringiensis Berliner.One of the first such plants is maize, Zea mays L., expressing the Bt toxin [1], because one of the main pests of maize in North America, the European corn borer, Ostrinia nubilalis Hubner (Lepidoptera: Pyralidae), is difficult to control by conventional pesticides, agronomic measures, or biological control agents [2]
We found that transient feeding on transgenic Bt maize had a negative effect on some body size parameters and, to a lesser degree, on fluctuating asymmetry (FA) in two hymenopteran parasitoids kept on two species of African stem borers, and these effects were stronger in the evolutionarily novel host–parasitoid associations than in the evolutionarily older, native ones
Wing length in parasitoids was sensitive to host plant effects: in all combinations but one, wing lengths were significantly lower on parasitoids developing on hosts subjected to transient feeding on Bt maize than on the control (F = 49.3, d.f. = 1,38, p = 0.0005 for C. flavipes on C. partellus; F = 5.7, d.f. = 1.38, p = 0.022 for C. sesamiae on C. partellus; F = 13.6, d.f. = 1.38, p = 0.001 for C. flavipes on S. calamistis)

Summary

Introduction

The use of genetic transformation technology in crops allowed several crop plants to express genes that encode insecticidal proteins (delta endotoxins) from the bacterium Bacillus thuringiensis Berliner. One of the first such plants is maize, Zea mays L., expressing the (activated) Bt toxin [1], because one of the main pests of maize in North America, the European corn borer, Ostrinia nubilalis Hubner (Lepidoptera: Pyralidae), is difficult to control by conventional pesticides, agronomic measures, or biological control agents [2]. Bt maize has been commercially grown in the USA since 1995 [3]. Maize is an important staple crop in sub-Saharan Africa (SSA), and is much affected by insect pests there [4]. In Africa, insect-resistant Bt maize is commercially grown only in South Africa [5], though several projects involving transgenic maize are underway.

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