Knowing Your Roots

Blog 35We all want the good guys to win, right?  Well, it is even more important in agriculture where there are good guys with wonderful names like assassin bugs and pirate bugs, which regularly seek out, kill and eat the bad guys that are eating our crops.  This is how nature keeps the balance between good and bad, and our potato and vegetable growers have learned nature’s tricks; they are masters at manipulating the system in their favor.  This concept is called biological control, and it uses a broad range of beneficial species that occur naturally in diverse ecosystems to attack pest species that feed on crops, keeping them at levels which do not harm the crops.

This process of one organism regulating populations of another is found throughout nature from microscopic bacteria to alpha predators, like wolves.  If we look with inquisitive eyes, we can see this in action in our very own back yards.  In production agriculture, biological control can be seen at a much larger scale.  It has become a vital component of the farmer’s toolbox that can be used in tandem with other approaches to keep pest populations below damaging levels.  The whole system is called Integrated Pest Management; the goal is to use pesticides only as a last resort when pests increase to damaging levels.  

Biological control can be achieved in multiple ways, and beneficial organisms (often called natural enemies) fall into three categories: predators that eat multiple prey; parasites that grow inside and usually kill their hosts; and pathogens (fungi, bacteria and viruses) that infect their targets and multiply inside the bodies causing disease, which then spreads to other hosts.  Biological control works best when growers can identify beneficial populations in the field and promote their success at the expense of pests. This can be done by ensuring that there is an adequate supply of prey, hosts or alternative food in times when pests are scarce.  This is achieved by providing diverse habitats where the natural enemies can survive.    Many growers are now planting multi-species windbreaks and hedges adjacent to fields where specific flowers, bushes, and landscape areas maintain the good guys close to fields by providing alternate food sources.  Some growers have even spread artificial food for natural enemies. In a remarkably successful example of biological control in greenhouse vegetables, pests are actually raised by growers and released in cucumbers and tomatoes to infest plants prior to releasing the natural enemies to control them.  The ability to monitor the competing pest and natural enemy populations and adjust them if needed is extremely important.  Therefore, growers carefully choose their pesticides and use ones which are very specific to manage the pest species without disrupting natural control.

Biological control works best when several natural enemies are involved, each exploiting a specific niche in the lifecycle.  Take for example, the Colorado potato beetle. This voracious pest is the most serious worldwide pest of potatoes and related crops.  There are several naturally occurring enemies that feed on all life stages of the Colorado potato beetle—eggs, larvae and pupae.  These include fungal diseases, parasitic flies, predatory stinkbugs, assassin bugs, pirate bugs, ground beetles and several species of the ever-lovely lady bug.  The ten-spotted ladybird beetle (one of many species of lady bug), for example, is a generalist predator that feeds on both eggs and young larvae, and they can cause as much as 35% mortality in first-generation Colorado potato beetles and up to 60% in the second generation.  Then, needing food later in the season, they anxiously await for the arrival of aphids.  This voracious lady beetle, which loves a tasty aphid, is already in place to thwart this new pest threat.

Parasites are more specific in what hosts they attack but are equally as deadly.  On Cole crops, for example, there are three destructive moth/butterfly pests whose young caterpillar can quickly reduce your cabbage or broccoli patch to tatters. Nature, however, has provided us with three very effective parasites— all in the wasp family— that can attack the pest complex at different life stages and provide effective damage control. The tiny Trichogramma wasp lays its egg in individual pest eggs, kills them and emerges as an adult to seek new hosts. The Diadegma wasp inserts its egg into larvae of the diamondback moth and kills it in the pupal stage, often achieving over 70% control. Perhaps the most remarkable of all, the Copidosoma wasp lays single eggs in small cabbage looper larvae where they divide into several hundred offspring, which let the pest survive to the pupal stage before emerging as a swarm of minute wasps which quickly overwhelm the next pest generation.

Biological control is an exciting and valuable process. We encourage you to actually look and see how this process occurs in your own home landscapes and gardens and experiment with ways to help it flourish.  Commercial vegetable growers in Central Wisconsin are using this dynamic in their production fields regularly, and the good ones are winning, helping us maintain a safe and plentiful food supply!

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