How to Ensure Your Predatory Insects Thrive

This article originally appeared in the August 2018 print issue of Cannabis Business Times. To subscribe, click here.

By releasing biological control agents such as parasitoids or predators, cannabis cultivators can control or eliminate harmful pest outbreaks.

The characteristics of an effective biological control agent include:

1. a high female reproduction rate,
2. short generation (maturation) time,
3. efficient dispersal (flight) capabilities and
4. a life cycle that is synchronized with generations of the prey or pest (meaning predators hatch at the same time as prey).

Furthermore, biological control agents must compete with pest-population development and reproduction to successfully regulate populations. In fact, the intrinsic rate of increase—the rate of increase of populations that reproduce within discrete time intervals and have generations that fail to overlap—of biological control agents must be similar to pests to provide sufficient regulation.

It also is important to understand the application procedures that will ensure success when using biological control agents, including:

• ordering biological control agents early,
• checking to make sure biological control agents are alive,
• releasing biological control agents immediately upon arrival, and
• applying biological control agents before pest populations reach outbreak proportions.

Another critical factor that can influence the effectiveness of biological control agents in regulating pest populations is environmental conditions associated with greenhouses and other indoor facilities, including: temperature, relative humidity, day length (photoperiod) and light intensity. These environmental parameters, if not appropriate for the specific biological control agent, can negatively affect foraging behavior, reproduction and survival. Therefore, the environment must be taken into consideration when implementing a biological control program.

Temperature

Temperature can alter the development and reproduction rates of biological control agents and pests. For example, the predatory mite Phytoseiulus persimilis is most effective at temperatures between 20°C and 30°C (68°F and 86°F) because at this temperature range, the development time of Phytoseiulus persimilis is shorter than its prey, the twospotted spider mite, Tetranychus urticae, so your predators will be fully grown faster than their prey/your pests. However, other predatory mites such as Neoseiulus californicus tolerate higher temperatures and a lower relative humidity than Phytoseiulus persimilis.

The optimal temperature for development, foraging and reproduction is 25°C to 30°C (77°F to 86°F). However, foraging activity decreases when temperatures exceed 30°C (86°F). In addition to reducing yield or killing your crop, temperatures greater than 30°C (86°F) will shorten the development time of the twospotted spider mite to less than Phytoseiulus persimilis, which will allow twospotted spider mite populations to undergo more generations than Phytoseiulus persimilis.

Other harmful pests can thrive in the temperature range best suited for cannabis cultivation. For example, whiteflies disperse more quickly and at farther distances at temperatures between 17°C and 30°C (63°F and 86°F), which may affect the success of the greenhouse whitefly, Trialeurodes vaporariorum (whose parasitoid is Encarsia formosa, a species of chalcidoid wasp), in regulating populations. This underscores the importance of timing the life cycle and release of the predatory insects to that of the prey.

To read the full article in Cannabis Business Times' August 2018 issue, click here.

Top photo courtesy of Adobe Stock