How is the velvetbean caterpillar primarily spread?

The velvetbean caterpillar is primarily spread by overhead sprinkler irrigation. This method of irrigation can create a moist environment conducive to the movement of the caterpillar, as the water droplets can carry eggs and larvae from one plant to another. When water is sprayed, it can dislodge caterpillars or their eggs, facilitating their spread to adjacent crops or areas.

In contrast, while soil disturbance, wind, and animal movement can contribute to the dispersal of various pests and pathogens, they are not the primary means of spreading the velvetbean caterpillar. Soil disturbance generally pertains to the movement of soil-borne organisms, wind tends to spread lightweight organisms or genetic material, and animals can carry pests but their role in specifically spreading the velvetbean caterpillar is not as significant as the water movement caused by overhead irrigation systems. Thus, overhead sprinkler irrigation plays an important role in the distribution and proliferation of this pest in agricultural settings.