.. Repelling locusts

Break into the van at the roadblock.

Check out the lockers. You will find a sonic repellent.

Drop it on the yard of the farmhouse. It will repel locusts if tuned into the correct frequency.

Examine the two corpses and the sticky note you found in the van.

The sticky note tells you the correct frequency. Compare the bug you find on one of the corpses on the images in the note.

You can set the frequency of the repellent with the remote controller.