In the light of new greenhouse technologies: 1. Plant-mediated effects of artificial lighting on arthropods and tritrophic interactions

This review describes the effects of the current and emerging lighting technologies on plants, and the plant-mediated effects on herbivorous and beneficial arthropods in high-technology year-round greenhouse production, where light quality, quantity and photoperiod differ from the natural environment. The spectrum provided by the current lighting technology, high-pressure sodium lamp (HPSL), differs considerably from that of solar radiation. The major plant-mediated effects on arthropods were predicted to result from (a) extended photoperiods and lower light integrals, (b) the attenuation of ultraviolet (UV) wavelengths, particularly UV-B, (c) the high red: far-red (R : FR) ratio and lower blue : red (B : R) in comparison with solar radiation and (d) the high proportion of yellow wavelengths during winter months. Of these light factors (a-d) (ceteris paribus), (a) and (b) were hypothesised to result in increased performance of herbivores in winter months, whereas the high R : FR ratio decreased herbivore performance or not affected it, at least when interlights are used. The predictions obtained on the basis of this review are also discussed in relation to the modifying factors prevailing in these production environments: enriched CO2 levels, high nutrient amounts, optimised irrigation and temperatures optimal for plants' needs. Based on the carbon/nitrogen and growth/differentiation balance theories, these modifying factors tend to produce plants that allocate most resources to growth at the expense of defensive secondary metabolism and physicochemical defensive structures. At the end, this review discusses knowledge gaps and future research prospects, in which light-emitting diodes, the emerging lighting technology, play an important role by enabling the targeted manipulation of plant responses to different wavelengths.