IPM is a holistic approach to managing insects, mites and diseases in the greenhouse. This is done through a combination of cultural, physical, biological and chemical practices, with chemical use typically being the last resort. In recent years, biological control of greenhouse pests has become the shining star of pest management. Rather than eliminating insects, mites and pathogens from the greenhouse, IPM brings in predatory or parasitic species to manage pests and diseases.
For this white paper, we will focus on the relationship between supplemental lighting, pest insects and mites, as well as biological control agents. And we will refer to pest insects and mites collectively as pests, and biological control agents simply as biologicals.
Pests and biologicals both have vision systems and photoreceptors that make them sensitive to light conditions. Many studies have observed the behavior of pests and biologicals under different light spectra, photoperiod and intensities.
Effect of photoperiod on diapause
When greenhouse conditions are unfavorable to insects and mites, many species enter diapause. This dormant state can be triggered by temperature, photoperiod, low food supply, population pressure and the presence of predators.
Of these, photoperiod is considered the strongest signal as it indicates the arrival of the winter season (Bryon et al., 2017). For the classic greenhouse crops (i.e., cucumbers, tomatoes, peppers and strawberries), a photoperiod of ≥16 hours is typically recommended. This is above the diapause threshold of most greenhouse pests and biologicals, so most species will not enter diapause. While greenhouse pests may not enter photoperiod-induced diapause, growers also need to think about their biologicals’ diapausing behavior.
For example, Orius insidiosus is highly effective against thrips during the summer but is notoriously difficult to establish in a greenhouse during the winter. However, supplemental lighting may make it easier to use Orius for winter production as growers will be able to provide the necessary photoperiod. Recent work by OMAFRA showed that while Orius develops rapidly under summertime conditions, females lived longer and produced more eggs under supplemental LED lighting for 20 hours. The researchers also reported that Dicyphus lived longer under high-intensity LED lighting (Labbé and McCreary, 2020).
Behavioral effects of light spectrum and light intensity
When transitioning towards lit production, it is important to communicate that to your biologicals provider and discuss which biologicals will perform well under supplemental lighting. For now, most of that focuses on applying the appropriate photoperiod to keep your biologicals out of diapause. In the future, we expect this to be finetuned according to light intensity and spectrum.
Various studies have explored the effect of light spectrum on greenhouse pests’ behaviors. Most insects and mites that we come across in greenhouse settings reportedly have trichromatic vision and are most sensitive to blue, green and ultraviolet light. For example, a study found that two-spotted spider mites may be driven to enter diapause under blue light (Suzuki et al., 2008). Another study then looked at western flower thrips and reported that thrips settled more under blue light and were possibly less active, whereas green wavelengths were linked to more feeding on leaves (Stukenberg et al., 2020).
Takeaway: Greenhouse pests and biologicals can see, and they are sensitive to certain wavelengths over others. Because of this, light spectrum and light intensity can affect the activity of pests and biologicals in the greenhouse.
Bryon, A., Kurlovs, A.H., van Leeuwen., T., Clark, R.M. 2017. A molecular-genetic understanding of diapause in spider mites: current knowledge and future directions. Physiological Entomology. 42(3): 211-224.
Labbé, R., McCreary, C. 2020. Arthropods and greenhouse lighting: Like moths to a flame. Greenhouse Canada.https://www.greenhousecanada.com/arthropods-and-greenhouse-lighting-like-moths-to-a-flame/
Stukenberg, N., Pietruska, M., Waldherr, A., Meyhofer, R. 2020. Wavelength-specific behavior of the western flower thrips (Frankliniella occidentalis): evidence for a blue-green chromatic mechanism. Insects. 11:423.
Suzuki, T., Yoshifumi, F., Amano, H., Takeda, M., Goto, E. 2008. Effects of light quality and intensity on diapause induction in the two-spotted spider mite, Tetranychus urticae. Applied Entomology and Zoology. 43(2):213-218.