Use of a Pollen-Based Diet to Expose the Ladybird Beetle Propylea japonica to Insecticidal Proteins

Xiaojie Zhang,Xinming Yin,Yunhe Li,Jörg Romeis,Kongming Wu,Yufa Peng

doi:10.1371/journal.pone.0085395

Abstract

A rape seed pollen-based diet was developed and found to be suitable for use in a dietary exposure assay for Propylea japonica. Using the diet, we established and validated a dietary exposure assay by using the protease inhibitor E-64 as positive control. Dose-dependent responses were documented for all observed life-table parameters of P. japonica including survival, pupation and eclosion rates, development time and adult weight. Results suggested that the dietary assay can detect the effects of insecticidal compounds on the survival and development of P. japonica. Using the established dietary assay, we subsequently tested the toxicity of Cry1Ab, Cry1Ac and Cry1F proteins that are expressed by transgenic maize, cotton or rice plants to P. japonica larvae. The diet containing E-64 was included as a positive control. Survival and development of P. japonica larvae were not adversely affected when the diet contained purified Cry1Ab, Cry1Ac, or Cry1F at 500 µg/g diet representing a worst-case exposure scenario. In contrast, P. japonica larvae were adversely affected when the diet contained E-64. The bioactivity and stability of the Cry proteins in the diet and Cry protein uptake by the ladybird larvae were confirmed by bioassay with a Cry-sensitive insect species and by ELISA. The current study describes a suitable experimental system for assessing the potential effects of gut-active insecticidal compounds on ladybird beetle larvae. The experiments with the Cry proteins demonstrate that P. japonica larvae are not sensitive to Cry1Ab, Cry1Ac and Cry1F.

Highlights

Before commercial cultivation, a new genetically engineered (GE) plant variety has to pass a rigorous environmental risk assessment
The objective of these studies was to identify the potential toxicity of the insecticidal proteins produced by the insect-resistant GE (IRGE) plants on surrogate species, i.e., on species that are representative of valued non-target organisms (NTOs) in the environment in which the IRGM crop is going to be released [1,4,5,6,7]
Pollen Consumption of P. japonica To establish a rape seed (Brassica napus L.) pollen-based diet that can be used to provide high doses of insecticidal compounds to P. japonica, we measured whether the larvae readily accept the rape seed pollen and how many pollen grains were consumed

Summary

Introduction

A new genetically engineered (GE) plant variety has to pass a rigorous environmental risk assessment. The non-target risk assessment follows a tiered framework that typically starts with laboratory toxicity studies that are referred to as Tier-1 assays and are conducted under controlled, worst-case exposure conditions [1,4,5] The objective of these studies was to identify the potential toxicity of the insecticidal proteins produced by the insect-resistant GE (IRGE) plants on surrogate species, i.e., on species that are representative of valued NTOs in the environment in which the IRGM crop is going to be released [1,4,5,6,7]. Ladybird beetles (Coleoptera: Coccinellidae) are well-known predators of Sternorrhyncha (Hemiptera), such as aphids, scale insects, psyllids, and white flies, and prey on a variety of other soft-bodied arthropods They play an important role in biological pest control in multiple crop systems including cotton, maize, and rice [8,9]. This group of insect predators has been in the focus of risk assessment studies with IRGE plants [10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26]

Methods

Results

Conclusion