By Caroline Stauffer SAO DESIDERIO, Brazil (Reuters) – Brazilian farmers are battling a voracious caterpillar that likely arrived from Asia, challenging the agricultural superpower’s widely touted mastery of tropical farming just as it is on the verge of becoming the world’s top soybean producer. The caterpillar, a variety known as helicoverpa armigera that thrives in dry heat, was spotted for the first time in the Americas on cotton farms in drought-prone western Bahia in early 2012, fuelling panic among farmers who had no idea what it was. The caterpillar was soon in soybean fields thousands of kilometers away thanks to the long-distance flying power of its moths, consuming everything from tomatoes to sorghum. While crop losses have thus far been limited, Brazil is now on red alert over the nation’s third major pest outbreak in 30 years.