Project Overview

Reports

Commodities

• Agronomic: sorghum (milo), sorghum (sweet)

Target Pests

• Target Pests: aphids

Practices

• Pest Management: behavioral control, biological control

• Production Systems: agroecosystems

Problem: A new sorghum pest, the sugarcane aphid (SCA), was first reported on sorghum in Beaumont, Texas during the summer of 2013. Since then, SCA has spread from Florida to California and it is now a serious problem for US sorghum. Growers in states affected by SCA have experienced yield reductions ranging from 20 to 100%. In the southern US, SCA feeds predominantly on grain sorghum and Johnson grass. In Johnson grass its susceptibility to predators and parasitoids is significantly lower than on sorghum. This is important because SCA in the southern US overwinters in Johnson grass, where it builds up large populations by the time sorghum is planted, spilling over into sorghum where it reaches population numbers that require insecticide sprays. Increasing SCA vulnerability to its natural enemies in Johnson grass can delay SCA population build up in sorghum, reducing the number of insecticide applications needed against this aphid.

Approach: The generalist parasitoid wasps Aphelinus nigritus and Lysiphlebus testaceipes are the two most common parasitoids of SCA in the US and are currently being considered as potential biological control agents. These wasps are known to feed on honeydew and use honeydew-associated cues to help locate potential hosts. Sugar, amino acid and fumaric acid concentration in honeydew varies significantly between SCA feeding grain sorghum and Johnson grass. Bacterial symbionts have been shown to alter honeydew nutritional quality and/or attractiveness for natural enemies in other aphid species.  Preliminary data from our laboratory, shows significant differences in microbiota composition between honeydew from sorghum and Johnson grass SCA. This proposal characterizes changes in honeydew bacterial communities and assesses whether chemical and microbial composition covary on Johnson grass and sorghum as well as explores the influence of honeydew bacterial composition in attracting natural enemies. 

Anticipated impact: Data generated by this project will inform future studies examining artificial manipulation of SCA honeydew aimed to increase SCA vulnerability to its natural enemies. Our long-term goal is to use this information to design future management practices aimed to increase the vulnerability of SCA to its parasitoids in Johnson grass so that fewer SCA move to sorghum fields.

Outputs:

1- Characterize variation in bacterial microbiota of SCA honeydew when feeding on Johnson grass and grain sorghum

2- Assess attractiveness of parasitoids to SCA honeydew from aphids feeding on Johnson grass and grain sorghum

Outcomes:

1-Determine if the bacterial microbiota of SCA honeydew differs between aphids feeding on Johnson grass and sorghum 

2-Determine whether host plant mediated differences in SCA honeydew influence parasitoid attraction