Invasion of fall armyworm led to the succession of maize pests in Southwest China

The invasive fall armyworm Spodoptera frugiperda (J. E. Smith) invaded Asia in 2018, colonizing the tropical and southern subtropical regions as well as migrating with the monsoons into Northeast Asia during spring and summer. This has resulted in widespread infestations, with significant impacts on maize production in various Asian countries. Previous studies have shown that the invasion of this pest can alter the species relationships of maize pests, but the actual impact on maize pest management is still unclear. This study investigated the changes in maize pest occurrence and pesticide use in the annual breeding areas of S. frugiperda in Yunnan Province and the Guangxi Zhuang Autonomous Region of China during 2017–2021, based on surveys and interviews with small farmers in maize production. The results showed that S. frugiperda has emerged as the dominant species among maize pests after invasion and colonization, replacing traditional pests such as Ostrinia furnacalis, Spodoptera litura, Agrotis ypsilon, and Rhopalosiphum maidis. The variety of pesticides used for maize pest control has changed from chlorpyrifos, lambda-cyhalothrin, and acetamiprid to emamectin benzoate-based pesticides with high effectiveness against S. frugiperda. Furthermore, the frequency of maize pest chemical applications has increased from an average of 5.88 to 7.21 times per season, with the amounts of pesticides used in summer and autumn maize being significantly higher than in winter and spring maize, thereby increasing application costs by more than 35%. The results of this study clarified the impact of S. frugiperda invasion on maize pest community succession and chemical pesticide use in tropical and south subtropical China, thereby providing a baseline for modifying the regional control strategies for maize pests after the invasion of this relatively new pest.