Insects and That
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Insects and That

Could breeding meaner predators boost pest control?

Robber fly attacking a smaller fly on a plant
Insect predators form a highly useful part of natural pest control

Biological controls are farmers’ friends, able to reduce populations of crop pests without the potentially-damaging use of pesticides.

Such controls can come in the form of pests’ natural enemies that are already present in agricultural environments, but increasingly, growers are adding to their ranks with commercially-reared specimens. This is particularly common for crops grown in greenhouses and polytunnels, where chances of escape are limited, so it’s easier to get more bug ‘bang for buck’.

Predators are a big part of biological control, given their nature to hunt down and feast on plant-eating arthropods. But wouldn’t it be better if they were guaranteed to be more aggressive than average? That’s certainly the question that researchers in Canada went out to answer.

Towards a super predatory bug?

Animal ‘personality’ is something of a hot topic. It is certainly is a ‘thing’, and applies to the bugs as much as anything else. Sure, they can’t consciously stand apart from the crowd, so it’s not a matter of character or disposition as we know it, but where there are observable differences in behaviour between individuals, it’s still considered personality.

The Canadian team ascertained that individuals of the predatory damsel bug, Nabis americoferus, which is a potential biocontrol of the plant bug Lygus lineolaris, do fall into distinctly aggressive and docile groups.

They worked this out by testing nine genetically-different lines with a lure, with responses recorded ranging from -2 for fleeing from the stimulus to +2 for launching an attack. As a side note, knowing how frustrating insect behavioural research can be, respect is due to the scientists for their patience in these tests.

The damsel bug Nabis americoferus, walking on the gound
Can a hyper-aggressive Nabis americoferus prevail?

Armed with this information, it could be concluded that the aggressive cadre would be more likely to do more damage to pest numbers than the rather more laissez-faire cohort. The remaining question that needed to be addressed was: would it be possible to selectively breed for such traits?

As it turned out, the answer was a fairly resounding yes. Three generations saw aggressiveness increased, while efficient selection for the trait was in place after five. Males were consistently more aggressive than females throughout breeding generations — no surprises there, some might say.

Little is simple in the predator-prey game

In theory, then, there is the potential to breed what appears to be a more valuable biocontrol ‘product’ — but there are possible downsides to such a move, which the researchers didn’t shy away from in their write-up.

Firstly, aggressiveness is likely to mean more willing to take on attacks against not just the organism the grower wants rid of, but members of its own species and other beneficial insects too. Would increased predation on the target pest outweigh the effects of the more scattergun approach to bug-on-bug violence? As it stands, this is unknown on an agri-ecosystem scale.

Another aspect where the classic ‘more research needed’ mantra rings true is in regards to how long the bred aggressiveness would last for in the field, given the tendency of insects to move about, find sub-niches and mate with whichever of its kind competition and circumstance favours.

It’s possible that after reaping the benefits of an initial burst of hyper-aggression, reversion to the mean would come apace. This might especially prove true if male-biased populations were bred for their aggressiveness, meaning that with fewer potential mates in the immediate surrounds, longer journeys to reproduce could be likely, increasing the chances of doing so with non-selected individuals.

From an anthropocentric point of view, it does seem that you can breed ‘better’ biocontrols — though as ever in ecology, things aren’t as straightforward as they seem. For growers, it may be that employing a genetically-unselected mix of predators and/or parasites, and ensuring that conditions are just right for their thriving, would be as good a bet as any in the quest for sustainable pest control.

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Gary Hartley

Gary Hartley

Writer of different things. Come for the insects, stay for the odd literary works, or vice versa. @garyfromleeds https://medium.com/insectsandthat