This is a continuation of my Integrated pest management (IPM) post. When the proper cultural and physical IPM controls are in place, but there is still a pest problem, the next tactic on the IPM list is biological control (biocontrol). Biocontrol is the use of living organisms such as insects, mites, nematodes, fungi and bacteria to control pests and diseases. Simply put, good bugs are used to fight the bad bugs. To be successful, biocontrol requires the support of cultural and physical controls but if done correctly it can be very effective in managing pests. Below is a video from Penn State University that touches on the subject of biocontrol:
In the attempt to reduce their pesticide use, PSU adopted biocontrols which they say has given them the opportunity to work with natural systems instead of against them. “Sometimes it is as simple as purchasing the right bug and releasing it in the right place at the right time, from there the good bugs take over and start controlling the bad ones.” With their experiences they said their pesticide use is substantially lower than it was before the used biocontrol. This was a huge plus for their scenario because it cut their pesticide costs as it promoted a healthier learning environment for their students.
So which bugs are good for which scenario? Here is a list copied straight from the University of Vermont’s agriculture website naming some of the beneficial insects and brief descriptions of what they can accomplish:
Aphidius of several species are tiny wasps that inject their eggs into the bodies of immature aphids (the nymphs). Aphidius wasps are parasitoids, meaning they reside in their host and eventually kill them. In this case, a wasp hatches inside an aphid and, as it grows, it consumes the aphid’s innards. When the food is gone, the wasp cuts a neat exit hole in the backside of the host and emerges, leaving behind a hollow aphid shell, or ‘mummy.’ Your friendly biocontrol distributor can help you select the species of Aphidius that will work best on the type of aphid pest you may have.
Aphidoletes aphidimyza is a midge that looks like a tiny mosquito. In the immature stage, this guy is a predator, meaning it hunts and consumes prey. The adults fly at night, locate colonies of aphids, and lay their eggs nearby. The eggs soon hatch into fast-moving orange larvae with a hankering for aphid meat. They run after the aphids, bite them on the knees, and inject them with a paralyzing toxin. Then, they literally suck their guts out. On a good day, a single A. aphidimyza larvae can chow down on 50 aphid Slurpies. They eat most all flavors of aphids, except melon aphids.
Many ladybugs are also predators. In the greenhouse, the convergent ladybeetle, Hippodamia convergens, feeds on aphids and spider mites. Ladybugs do not always provide successful, long-term control but they are useful to “knock down” an infestation. These predators are collected in the wild, but availability is good, except during the early summer months when supplies may be sold out. Ladybugs can be stored in the refrigerator for several weeks and released one handful at a time. They are usually thirsty when released, so plants should be misted prior to release. Releasing them in the evening is also important.
Encarsia formosa is a tiny parasitoid wasp used to control greenhouse whitefly. It lays its eggs inside whitefly larvae, which young wasps later consume and kill. Encarsia formosacomes to the grower as parasitized whitefly pupae stuck to small cards. The cards are easy to hang on plants below the canopy, out of direct sunlight. The wasps do best when daytime temperatures exceed 72 degrees and nights are above about 60 degrees. At lower temperatures, and at low light levels, the whiteflies reproduce too fast for Encarsia formosato control them.
Phytoseiulus persimilis is a predatory mite for control of two-spotted spider mite. This is a case of a fast mite that can run down and eat slower mites. The predator is shipped mixed with vermiculite or bran and must be released carefully by sprinkling a little on every infested leaf. It becomes established in the crop in about one week. Predatory mites prefer moderate temperatures and humid conditions (60 to 90% relative humidity). Spider mite populations have a tendency to explode when it gets hot and dry, so early or preventative releases of Phytoseiulus persimilis are key to success.
Steinernema species and Heterorhabditis species are parasitic nematodes that attack a variety of soil dwelling insect pests. These include the larvae, or grubs, of certain beetles, and weevils. The nematodes enter the pest larvae then they multiply inside their bodies, killing them and then leaving by the thousands, seeking out other susceptible larvae. A moist soil environment is a requirement for success with parasitic nematodes. The nematodes can be supplied in a spray concentrate or a moist granular carrier. Some growers apply them using injector systems or diluting them with water and using a pump sprayer, hose end sprayer, watering can or pail.
Brutal! Biocontrol is essentially the same as unleashing biological warefare in your greenhouse. Using insects to fight insects almost sounds too easy, but there are several things to keep in mind when using biocontrol:
- No single pest control method is 100% effective.
- This method often involves more work at first than chemical control, and it may require changes in production methods.
- The good bugs are often highly susceptible to pesticides. When choosing pesticides, select those with the shortest residual life and the highest specificity.
- Biocontrols work slowly, they are best used when pest numbers are fairly low.
- Most predators and parasites perform best at moderate temperatures (65-85°F) and humidity (60-90%).
- If the greenhouse is allowed a dormant period (either very hot or very cold), the good bugs will die.
- If all the plants leave the greenhouse, so will the good bugs.
- If all the pests are destroyed, the good bugs will starve.
- Different types of plants have different reactions to biocontrol.
Insects and diseases are major challenges in greenhouse production, but they can be mitigated with Integrated Pest Management. Through the use of physical, cultural, and biological tactics pests can be kept at a manageable level without using harmful chemicals to fully eliminate them. IPM is the opportunity to grow healthy greenhouse crops by using methods that are safe, profitable, and environmentally compatible.
Do you have any experience with this topic? How do you feel about using insects to fight insects? Please share your thoughts in the comment section below.