- Parasitic monsters, genetic manipulation, being forced to watch in silence as someone eats you alive, tomatoes… This story has it all.
According to the tagline of the 1979 scifi horror classic Alien, no one can hear you scream in space. Apparently, that’s also true for gardens.
Did you know that plants are actually able to call for help when they’re being attacked? Indeed, to paraphrase another science fiction bestseller, they have no mouth but they must scream.
Only, the plants’ pleas for aid are not based on sound. Instead, they release a variety of chemicals – depending on the plant – that attract animals to help them or warn other plants around them about the danger.
Researchers have now discovered that a certain species of caterpillar employs a horror movie-inspired method to silence its victim, the tomato. The plant can scream all it wants, but no one will ever hear it – while the caterpillar feasts on its living tissues.
Nature is cruel, in case you hadn’t already noticed.
Revenge of the Body Snatcher Wasp
But the caterpillars actually have a very good reason to gag the tomato plant. If they didn’t, their life would very soon turn into a horror movie all of its own, the study published in the journal New Phytologist explains.
When a tomato plant finds itself under attack, for example by the caterpillar, it releases what are called herbivore-induced plant volatiles (HIPV). As mentioned, these chemicals are designed to bring in help in some way or form.
In this case, the tomato plant has learned to enlist the caterpillar’s natural enemy to fight the threat. The HIPVs the tomato emits attract a certain kind of parasitic wasp.
This particular wasp uses live caterpillars in its reproductive cycle. Namely, it lays its eggs inside the caterpillar while it’s still fresh and squirming.
The eggs will eventually hatch inside the still-living caterpillar, and the larvae start consuming their host from the inside out. Once they’re big enough, they will burst out of the ‘pillar like the offspring of the xenomorph creature from Alien.
Seriously, everybody in this story has been watching way too many scifi flicks.
The Silence of the Tomatoes
However, the scientists observing the phenomenon noticed that sometimes the wasps just didn’t show up. To their minds, this begged the question: are the caterpillars doing something to bring forth the silence of the tomatoes?
It turns out that they indeed are. The study’s lead author Po-An Lin, from the Department of Entomology at Pennsylvania State University, told Phys.org that the secret to silencing the tomato is in the caterpillar’s saliva.
As the caterpillar starts munching on the tomato’s leaves, it injects its enzyme-laden saliva into the plant. These enzymes prevent the pores in the leaves from opening up as wide as they usually do.
As a result, the tomato can’t emit as much of the wasp-attracting HIPVs. The wasps can’t hear (or smell) the call for aid, and therefore never arrive to help.
All the tomato can do is sit in silence while the caterpillar slowly consumes its body.
Modifying the Caterpillar
To test whether this was actually the case, Lin’s team measured both the width of the tomato’s leaf pores and the level of HIPVs that it emits. Then, they unleashed hordes of caterpillars onto their unsuspecting test subjects.
But there was one catch. Some of the caterpillars were normal, but others had been genetically modified for this experiment.
To be precise, Lin’s team used the CRISPR technology to erase the gene that produces the tomato-silencing enzymes in the caterpillar’s saliva. After both the modified and natural caterpillars had feasted on the tomatoes, the team repeated their earlier measurements.
They found out that the tomatoes that were eaten by the modified caterpillars produced HIPVs as usual. But those that were attacked by the unmodified bugs had their pore widths significantly reduced.
The results of the experiment were clear. The caterpillars indeed gag the tomato so it can’t scream.
Farmers Call for Aid
The scientists note that their research could be beneficial for agriculture. The caterpillars they studied – known among other names as corn earworms and cotton bullworms – don’t limits their diets to tomatoes, after all.
As their multitude of names implies, these ‘pillars like just about any crop. Corn, cotton, soy, strawberry, and hemp farmers across North and South America regularly encounter these pests in their fields.
Lin suggests that it might be possible to selectively breed tomato plants to resist the caterpillar saliva. This would result in hardier plants and increased yields.
Over the last 20 years, many other studies have been published on caterpillar saliva’s effects on other crops. For example, research has shown that some ‘pillars lower the amount of nicotine in tobacco leaves, making the plants safe for them to eat.