Development and validation of a dynamic action threshold for sugarcane aphids in sorghum
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abstract
The invasive sugarcane aphid (Melanaphis sacchari) is threatening sorghum productionin the U.S. Outbreaks of the aphid have caused significant economic losses to sorghum production since they began colonizing the crop in 2013. Sorghum is an important crop in the U.S. In 2016, nearly 6.2 million acres of grain sorghum valued at $1.35 billion were harvestedand sugarcane aphid infestations were confirmed in 98% of the sorghum producing regions in the country.Insecticides are currently the only means of suppressing sugarcane aphids in sorghum, but are limited to two insecticides with similar mode of action, which is likely to result in development of insecticide resistance.Thus, there is an urgent need to explore and integrate additional, non-chemical management tactics that will maintain profitability of sorghum production regardless of insecticide efficacy. To address this need, we propose to use greenhouse experiments todevelop and then validate in the fielddynamic action thresholds that account for the suppressive effects of predators and plant resistance. The goal of this research is to identify predator densities that maintain or suppress sugarcane aphids below their economic injury level in resistant and susceptible varieties of sorghum. Our ultimate aim is to reduce the number of insecticide applications in sorghum and increase sorghum profitability.Impacts of the proposed work will benefit sorghum production not only in Texas but also throughout the southeastern U.S. and High Plains, where sugarcane aphids colonize sorghum during vegetative and reproductive stages, respectively. Dynamic action thresholds that provide effective suppression of sugarcane aphid in susceptible and resistant sorghum regardless of timing of aphid colonization will reduce the number of insecticide applications without diminishing sorghum yield and can be implemented across major sorghum-producing regions in the U.S. This outcome will have environmental benefits of reducing exposure of predators and pollinators associated with sorghum to toxins, decrease human exposure to insecticides during applications, and improve the net profits of sorghum production by eliminating or reducing the number of required insecticide sprays. In the long term, outcomes of this work have the potential to improve sorghum profitability nationwide and as a result contribute to increased sorghum acreage.
