Effects of transgenic Bt corn pollen on a non-target lycaenid butterfly, Pseudozizeeria maha

Abstract

To evaluate the effect of pollen released from transgenic insecticidal corn on non-target lepidopteran insects, corn pollen deposition density on the leaves of sunflower and black nightshade was measured near a cornfield. At 12 d from the start of anthesis, the highest cumulative pollen density on leaves was approximately 160 grains per cm 2 at 1 m from the edge of the cornfield, falling to 20 grains at 5 m and less than 10 grains at 10 m. The pollen density calculated using a mathematical model in a previous study evidently had overestimated values. To evaluate precisely the effect of corn pollen expressing Bacillus thuringiensis (Bt) endotoxin (Cry1Ab) on the survival of lepidopteran larvae, we improved the bioassay methods using the pale grass blue, Pseudozizeeria maha, the leaf disc of the wood sorrel, Oxalis corniculata, and transgenic Bt corn (Event-176). When the surface of the leaf was pretreated with a small amount of 80% acetone solution, the preselected pollen dose was successfully applied onto the leaf disc. Larval survival of P. maha was significantly affected at pollen density of more than 20 grains per cm 2 on the leaf disc. It is unlikely that pollens from Bt corn expressing Cry1Ab have wide-scaled deleterious effects on non-target P. maha near cornfields, because of low pollen deposition dose on the leaves.

Laboratory evaluation of effects of transgenic Bt corn pollen on two non-target herbivorous beetles, Epilachna vigintioctopunctata (Coccinellidae) and Galerucella vittaticollis (Chrysomelidae)

“…Therefore, it is worth evaluating the effect of pollen exposure on non-target herbivorous beetles which live on wild host plants near cornfields. This study investigated larval survival and development using leaf discs exposed to Bt corn pollen for 10-day periods since pollen deposition was most abundant at 3 to 7 d after anthesis and markedly decreased from 10 days in cornfields (Pleasants et al, 2001;Shirai and Takahashi, 2005). G. vittaticollis did not show any adverse larval survival and development between doses of 500 and 2,000 grains/cm 2 of Bt corn pollen.…”

“…According to Shirai and Takahashi (2005), a corn pollen suspension containing the pre-selected pollen dose was prepared. Before larval bioassay, the number and weight of corn pollen grains on a micro-cover grass were determined with a stereomicroscope (E400, Nikon Eclipse, Tokyo, Japan) and a micro-balance (MX-5, Mettler Toledo, Tokyo, Japan) to weigh 1,000 grains of pollen, since pollen weight fluctuates under storage conditions.…”

“…When 1,000 grains of pollen weighed 0.245 mg, 18.86 mg (= 1.54ϫ0.245ϫ1,000Ϭ20) of pollen was added to 1 ml of distilled water in a vial. Unlike a leaf disc of wood sorrel, Oxalis corniculata (Shirai and Takahashi, 2005), pretreatment with a small amount of 80% acetone solution on the leaf disc was unnecessary since the leaf surfaces of S. nigrum and R. japonicus are hydrophilic.…”

“…These studies have revealed that only a small number of corn pollen are deposited onto the leaves of host plants and there are few risks to this butterfly in and near cornfields (Pleasants et al, 2001;Jesse and Obrycki, 2003;Anderson, 2004;Lang et al, 2004). The author also confirmed that the highest cumulative pollen dose on leaves was approximately 160 grains/cm 2 at 1 m from the edge of cornfields, and suggested the following procedure of risk assessment for Bt corn pollen: First, the Bt endotoxin level in corn pollen is evaluated by enzyme linked immunosorbent assay (ELISA), and then a bioassay using non-target insect larvae should be conducted in the laboratory when significant expression is detected in corn pollen (Shirai and Takahashi, 2005).…”

“…At that time, a bioassay method using native non-target coleopteran species had not yet been developed in Japan, so the potential risk of pollen exposure to non-target beetles was evaluated based on an artificial diet overlay bioassay using larvae of the Colorado potato beetle, Leptinotarsa decemlineata (Say) (Yamane, 2005). Subsequently, Shirai and Takahashi (2005) developed a simple bioassay method to evaluate the effect of pollen exposure on non-target lepidopteran larvae, which is also suitable for risk assessment in coleopteran species.…”