Are These Citrus Pests Afraid of Heights?

Pests don't appear to be as fearless in their pursuit for food as we might think. The Asian citrus psyllid (ACP), an invasive pest that recently found its way into Florida and Puerto Rican citrus farms, seems to avoid heights, according to new research, offering some new clues about the voracious insect's vulnerabilities.

That's at least according to a study recently published in the Journal of Economic Entomology, which details how a team of researchers decided to investigate anecdotal evidence that the ACP (Diaphorina citri) is far less abundant, even in heavily invaded regions, at higher elevations.

Choosing 17 different sites between 10 and 880 meters (33-2,887 feet) above sea level, the researchers monitored citrus trees and other common chew-toys of the ACP using yellow sticky traps for two years.

As expected, the traps were full of the tiny insects at low elevations. However, as elevations increased, ACP populations decreased.

"There was a strong trend in both years for decreasing psyllid abundance with increased elevation based on the number of psyllids captured on traps and the proportion of trees shown to be infested," the researchers wrote. "No psyllids were collected at an elevation of >600 m."

The researchers also found no evidence of greening disease - an illness transported by the pests to new trees, at the highest elevations. Interestingly, there doesn't seem to be any physiological explanation for this behavior.

Is this to say that the insects suffer from an irrational fear of heights (acrophobia)? Probably not, but the researchers do admit that the reason behind ACP avoiding heightened elevations remains a mystery. It may have to do with environmental factors on the insects not yet observed, such as the effects of short wave radiation, or elevated air pressure.

What is known, is that farmers will do well to relocate their citrus nurseries to areas 600 meters above sea level when possible.

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