Sweet Corn Sentinel Monitoring for Lepidopteran Field-Evolved Resistance to Bt Toxins

As part of an insect resistance management plan to preserve Bt transgenic technology, annual monitoring of target pests is mandated to detect susceptibility changes to Bt toxins. Currently Helicoverpa zea (Boddie) monitoring involves investigating unexpected injury in Bt crop fields and collecting larvae from non-Bt host plants for laboratory diet bioassays to determine mortality responses to diagnostic concentrations of Bt toxins. To date, this monitoring approach has not detected any significant change from the known range of baseline susceptibility to Bt toxins, yet practical field-evolved resistance in H. zea populations and numerous occurrences of unexpected injury occur in Bt crops. In this study, we implemented a network of 73 sentinel sweet corn trials, spanning 16 U.S. states and 4 Canadian provinces, for monitoring changes in H. zea susceptibility to Cry and Vip3A toxins by measuring differences in ear damage and larval infestations between isogenic pairs of non-Bt and Bt hybrids over three years. This approach can monitor susceptibility changes and regional differences in other ear-feeding lepidopteran pests. Temporal changes in the field efficacy of each toxin were evidenced by comparing our current results with earlier published studies, including baseline data for each Bt trait when first commercialized. Changes in amount of ear damage showed significant increases in H. zea resistance to Cry toxins and possibly lower susceptibility to Vip3a. Our findings demonstrate that the sentinel plot approach as an in-field screen can effectively monitor phenotypic resistance and document field-evolved resistance in target pest populations, improving resistance monitoring for Bt crops.

Sebelas Tahun Perkembangan Jagung Bt dan Statusnya secara Global

<p>Major insect pests of corn are the Asian<br />corn borer, the European corn borer, and the corn root<br />worm. The value of crop losses due to the insect pests in<br />America is $2.6 billion, Asia $1.6 billion, Africa $0.8 billion,<br />and Europe $0.6 billion. Prior to the use of Bt corn, farmers<br />used a lot of insecticides to control the insect pests.<br />Following introduction of the Bt corn in 1996, this crop has<br />been grown over 21 million hectares by millions of farmers<br />from 13 countries in North America, Latin America, Asia,<br />Africa and Europe. Globally, the farmers had been benefited<br />by grownt the Bt corn. The benefits varies, dependent on<br />countries and level of the corn borer infestations. In 2001,<br />the US farmers gained $125 million benefit from growing the<br />crop. In 2002, farmers in Spain gained 11-15 million benefit<br />from the Bt corn alone. During the period of 2003-2005, corn<br />farmers in the Philippines gained $8 million from the Bt corn.<br />Bt corn has not been grown commercially in Indonesia,<br />although Bt corn MON810 has been declared as save to<br />release in the environment by the Indonesian Biosafety<br />Committee. In 2001-2002, farmers in South Sulawesi with<br />had grown Bt cotton, this was the first time Bt crop in the<br />country since the placement and implementation of the<br />biosafety regulation by the Indonesian Government in 1998.</p>

Plot Refugi untuk Pengelolaan Resistensi Hama terhadap Tanaman Transgenik Bt

<p>Refugea Plot as Insect Resistance Management in<br />Transgenic Bt Crops. Bahagiawati. The objective of this<br />review is to share information on several cases of target<br />insects became resistance to transgenic-Bt crops in the field<br />and the refuge strategy used to manage this problem. Bt<br />corn and Bt cotton have been planted widely for several<br />years globally. One of the risks of planting transgenic Bt crop<br />is the ability of the target insects adapted to the Bt protein<br />and caused the resistance breakdown the transgenic Bt<br />plants. This phenomenon was hypothesized in early 1990s<br />based on the cases of several insects resistance to microbial<br />Bt sprayed in laboratories and in the field. The mode of<br />action of the pest resistance to Bt-toxin have been studied in<br />several laboratories. In USA, to avoid the target insect<br />resistance to transgenic Bt crops, a program called Insect<br />Resistance Management (IRM) has been applied since 2001<br />for farmers growing Bt crops. Lately, there have been some<br />reports of target insects became resistance to cry1F, cry1Ab,<br />and cry1Ac in transgenic Bt crops. A report informed about<br />the resistance of target insect in Puerto Rico was published<br />in 2006, and so in South Africa in 2006/2007, and the last one<br />in India in 2009. To avoid target’s insect become resistance<br />to Bt crops, a program called structural IRM and unstructural<br />IRM were introduced and applied in several<br />countries. One of the components of IRM is planting refuge<br />plot, a plot that planting with isogenic line of Bt crops in/near<br />by the area of Bt crops. This review will discuss about the<br />cases of target insect became resistance to Bt crops in the<br />field, mode of action of insect resistance to Bt, the model of<br />IRM program in USA and the Philippines and finally the<br />recommendation for Indonesia to prepare its IRM program<br />for implementing Bt crops.</p>