Deleterious Effects of Uv-B Radiation on Herbivorous Spider Mites: They Can Avoid It by Remaining on Lower Leaf Surfaces

Abstract

The herbivorous spider mite Tetranychus urticae usually remains on the lower leaf surfaces of its host plants. Although terrestrial animals are generally thought to be well protected from damage because of UV radiation, insect herbivory frequently increases when solar UV-B (280-315 nm) radiation is attenuated. As UV transmission through leaves is generally low because of the accumulation of compounds that act as selective sunscreens (e.g., phenolics), we hypothesized that T. urticae avoids solar UV-B radiation by staying on lower leaf surfaces. We examined whether artificial UV irradiation and solar UV affected the survival and reproduction of T. urticae and whether staying on lower leaf surfaces was beneficial to their performance under ambient UV radiation. We found that T. urticae was not well protected from UV-B radiation, because artificial UV-B irradiation strongly decreased survivorship and egg production. More importantly; compulsory solar UV irradiation treatments also had lethal effects on T. urticae, whereas the mites could avoid them if they remained on the lower leaf surfaces of their host plants. These results showed that access to habitats protected from sunlight, such as lower leaf surfaces, is likely essential for T. urticae survival under ambient UV-B radiation. The lethal effects of solar UV radiation may also affect the population dynamics of spider mites, and habitat (resource) limitation may increase the probability of interspecific interactions, such as competition and predation. In turn, the occurrence of these interactions in sheltered areas may be associated with observed increases in herbivory under conditions of solar UV-B-attenuation.

Difference between Nighttime and Daytime UV-B Irradiation with Respect to the Extent of Damage to Perilla Leaves

“…Artificial UV-B irradiation was reported to reduce the incidence of fungal diseases, such as strawberry powdery mildew (Kanto et al, 2009(Kanto et al, , 2014, rose powdery mildew (Kobayashi et al, 2013), and eggplant leaf mold caused by Mycovellosiella nattrassii (Oka et al, 2011). Moreover, it was reported that UV-B irradiation hindered the survival and reproduction of the herbivorous spider mite Tetranychus urticae (Murata and Osakabe, 2013;Ohtsuka and Osakabe, 2009). The mortalities of adult females, larvae, and eggs of T. urticae were proportional to the cumulative UV-B irradiance to which they were exposed (Murata and Osakabe, 2013).…”

Cross-talk between high light stress and plant defence to the two-spotted spider mite in Arabidopsis thaliana

“…While cited reports point to the reaction of stressed plants, there could be a direct light influence on herbivores. For instance, UVA and UVB radiation have an effect on mite survival, reproduction, and spatial distribution on host-plants (Ohtsuka and Osakabe 2009;Sakai and Osakabe 2010). It was also determined that visible light treatment after UVB treatment caused photoreactivation of adult females, resulting in the increased survival recovery of T. urticae and Tyrophagus putrescentiae (Santos 2005), and effects on the egg hatchability of T. urticae as well as predatory mite (Koveos et al 2017;Murata and Osakabe 2014).…”

Do plant mites commonly prefer the underside of leaves?

“…However, recent studies demonstrated that solar UVB radiation also largely affected the behavior of spider mites (Ohtsuka and Osakabe 2009;Sakai and Osakabe 2010) and phytoseiid mites (Onzo et al 2010), and possibly restricted their foliar surface availability. Since Phytoseius nipponicus Ehara was the phytoseiid mite species commonly observed on VEP (Sudo et al 2010) and that preyed upon B. obovatus eggs (M. Sudo, unpublished data), it is likely that P. nipponicus was also vulnerable to UVB radiation as well as other phytoseiid mites.…”

“…Recently, the effects of solar UV radiation on survival and spatial distribution between the upper and lower leaf surfaces have been investigated in herbivorous spider mites (Ohtsuka and Osakabe 2009;Suzuki et al 2009;Sakai and Osakabe 2010) and predaceous phytoseiid mites (Onzo et al 2010). 'Reverse gravity' experienced by inhabitants on the upper or lower leaf surfaces was also suggested to affect the distribution of a spider mite, i.e., mites preferred the leaf surface facing downward, regardless whether this was the morphological adaxial or abaxial side (Li and Margolies 1991).…”