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Squash bugs with symbiotic bacteria in their guts. The bacteria have been tagged with fluorescent proteins
Courtesy of Scott Villa
Shortly after hatching, young squash bugs go on a mission to find and eat adults’ faeces so they can acquire bacteria they need to survive. They are forced into this unusual behaviour because they don’t inherit the vital bacteria from their parents.
Squash bugs (Anasa tristis) are agricultural pests that commonly attack courgette, also known as zucchini, and pumpkin crops in North and Central America.
The bugs have a symbiotic relationship with Caballeronia bacteria, which live in their guts and are crucial for their growth, development and survival.
Other species that require symbiotic bacteria, like stink bugs, get immediate access at birth because their mothers leave bacteria-rich faeces on top of their eggs.
However, squash bugs aren’t left the same inheritance, says Scott Villa at Davidson College in North Carolina. “Squash bugs need [these bacteria] to live, yet, for such an important piece of their lives, parents do not simply give it to their offspring,” he says. “Instead, they basically leave it up to each generation to find it on their own in the environment.”
Villa and his colleagues discovered that newborn squash bugs – called nymphs – do this by seeking out and feeding on the faeces of adult squash bugs, which are packed with Caballeronia bacteria.
The team placed nymphs in an arena in which they could choose to move towards saline solution or adult faeces. In 99 per cent of trials, the nymphs headed to the faeces, which they liquefied with their saliva and slurped into their mouths.
Separate experiments found that the nymphs could still locate adult faeces in the dark and from long distances away.
The nymphs had been provided with ample summer squash to munch on, so they didn’t appear to be eating the faeces out of hunger. Plus, once they had acquired Caballeronia bacteria, they didn’t seek out any more faeces and concentrated on eating the summer squash.
Interestingly, the nymphs mostly avoided the faecal matter of a related species called Anasa andresii, even though it also contained Caballeronia bacteria, suggesting that the nymphs are precisely attuned to the faeces of their own species.
Villa believes that squash bug parents don’t need to directly pass their bacteria to their offspring because adults and nymphs live in close-knit communities, meaning there are ample adult faeces lying around for nymphs to feed on and acquire the bacteria themselves.
The researchers hope their findings will lead to new strategies for eliminating the pests from crops.
“Squash bugs can be a devastating pest, and we now know a key vulnerability in their life cycle,” says Villa. “If we can somehow break their ability to find their [bacteria] or remove their [bacteria] from the environment, we can halt population growth.”
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