UV-B susceptibility and photoreactivation in embryonic development of the two-spotted spider mite, Tetranychus urticae

Interactive effects of changes in UV radiation and climate on terrestrial ecosystems, biogeochemical cycles, and feedbacks to the climate system

Terrestrial organisms and ecosystems are being exposed to new and rapidly changing combinations of solar UV radiation and other environmental factors because of ongoing changes in stratospheric ozone and climate. In this Quadrennial Assessment, we examine the interactive effects of changes in stratospheric ozone, UV radiation and climate on terrestrial ecosystems and biogeochemical cycles in the context of the Montreal Protocol. We specifically assess effects on terrestrial organisms, agriculture and food supply, biodiversity, ecosystem services and feedbacks to the climate system. Emphasis is placed on the role of extreme climate events in altering the exposure to UV radiation of organisms and ecosystems and the potential effects on biodiversity. We also address the responses of plants to increased temporal variability in solar UV radiation, the interactive effects of UV radiation and other climate change factors (e.g. drought, temperature) on crops, and the role of UV radiation in driving the breakdown of organic matter from dead plant material (i.e. litter) and biocides (pesticides and herbicides). Our assessment indicates that UV radiation and climate interact in various ways to affect the structure and function of terrestrial ecosystems, and that by protecting the ozone layer, the Montreal Protocol continues to play a vital role in maintaining healthy, diverse ecosystems on land that sustain life on Earth. Furthermore, the Montreal Protocol and its Kigali Amendment are mitigating some of the negative environmental consequences of climate change by limiting the emissions of greenhouse gases and protecting the carbon sequestration potential of vegetation and the terrestrial carbon pool.

Mechanisms underlying the impact and interaction of temperature and UV-B on the hatching of spider mite and phytoseiid mite eggs

BACKGROUND

A spider mite control method using night-time ultraviolet (UV)-B irradiation was recently developed for strawberry greenhouses (UV method). The control effect of this UV method is negatively affected by increasing temperature. Tetranychus urticae eggs are more resistant to a single dose of UV-B irradiation than Neoseiulus californicus eggs. By contrast, N. californicus can better survive nightly UV-B irradiation with the UV method compared with T. urticae. To elucidate the mechanism underlying these phenomena, we explored the hypotheses that higher temperature promotes photoenzymatic repair (PER) and that mortality is determined by UV-B susceptibility in the embryonic stage exposed to UV-B.

RESULTS

PER efficacy was not promoted by increasing temperature. The lowest hatchability (around zero) of T. urticae eggs after a single dose of UV-B irradiation (0.288 and 0.432 kJ m^-2 ) without photoreactivation was seen in the morphogenesis stages between "cleavage ended" and "eye points became colored". Based on these results, we developed a linear function of daily UV-B irradiance and deviation of cumulative irradiance during vulnerable embryonic developmental phases from 50% lethal dose (LD₅₀ ) after a single dose of UV-B irradiation. The difference between T. urticae and N. californicus and changes in UV-B vulnerability due to temperature could be explained by this simple relationship.

CONCLUSION

Slower development in T. urticae than N. californicus in nature and developmental delay under low temperatures increase the ovicidal effects of the UV method. This shows the advantage of the simultaneous use of the UV method and biological control, contributing to the development of integrated pest management. © 2022 Society of Chemical Industry.

Acaricidal efficacy of ultraviolet-C irradiation of Tetranychus urticae adults and eggs using a pulsed krypton fluoride excimer laser

BACKGROUND

Pulsed ultraviolet (UV)-C light sources, such as excimer lasers, are used in emerging non-thermal food-decontamination methods and also have high potential for use in a wide range of microbial decontamination applications. The acaricidal effect of an experimental UV-C irradiation device was assessed using female adults and eggs of a model organism, the two-spotted spider mite Tetranychus urticae.

METHODS

UV-C light was generated by a pulsed krypton fluoride excimer laser operating at 248-nm emission wavelength. The pulse energy and pulse repetition rate were 5 mJ and up to 100 Hz, respectively. The distance from the light source to the target was 150 mm; the target surface area was 2.16 cm2. The exposure time for the mites and fresh eggs varied from 1 to 4 min at 5-300 mW, which corresponded to UV doses of 5-80 kJ/m2. Post-irradiation acaricidal effects (mite mortality) were assessed immediately and also measured at 24 h. The effects of UV-C irradiation on the hatchability of eggs were observed daily for up to 12 days post-irradiation.

RESULTS

The mortality of mites at 5 and 40 kJ/m2 was 26% and 92%, respectively. Mite mortality reached 98% at 80 kJ/m2. The effect of exposure duration on mortality was minimal. The effect of irradiation on egg hatchability was even more significant than that on adult mite mortality, i.e. about 100% egg mortality at an accumulated dose of as little as 5 kJ/m2 for each exposure time.

CONCLUSIONS

A high rate of mite mortality and lethal egg damage were observed after less than 1 min of exposure to 5 mJ UV-C pulsed irradiation at 60 Hz. Pending further developments (such as beam steering, beam shaping and miniaturisation) and feasibility studies (such as testing with mites in real-life situations), the reported results and characteristics of the UV-C generator (modulation of energy output and adaptability to varying spot sizes) open up the use of this technology for a vast field of acaricidal applications that require long-range radiation.

Strawberry pollen as a source of UV-B protection ingredients for the phytoseiid mite Neoseiulus californicus (Acari: Phytoseiidae)

BACKGROUND

A new physical control method using ultraviolet-B (UV-B) lamps and light-reflecting sheets (UV method) significantly suppressed a spider mite population on greenhouse strawberries. Although UV-B radiation may adversely affect the survival of phytoseiid mites, previous research has suggested that Neoseiulus californicus can improve its survival on exposure to UV-B irradiation by consuming antioxidants contained in tea and peach pollen. In this study, we evaluated strawberry pollen as an alternative food source for N. californicus and examined whether antioxidants in the pollen mitigated UV-B damage to N. californicus.

RESULTS

The fecundity of N. californicus females reared on Tetranychus urticae decreased on shifting their diet to pollen. By contrast, females reared continuously on strawberry pollen produced as many eggs as females reared continuously on T. urticae. Survival and fecundity after UV-B irradiation were higher in females on the pollen diet. Oxygen radical absorbance capacity analysis revealed that the high antioxidant activity of strawberry pollen was due to four hydroxycinnamoyl spermidine derivatives.

CONCLUSION

Strawberry pollen was an adequate alternative food source for N. californicus. Feeding on strawberry pollen, which contains spermidine derivatives with high antioxidant activity, mitigated UV-B damage. This shows the potential of combining the UV-method with N. californicus for controlling T. urticae in strawberries.

Effects of Growth Phase and Ultraviolet-B Pretreatment in Perilla Leaves on the Two-Spotted Spider Mite

Perilla, Perilla frutescens (L.) Britton var. crispa (Thunb.) H. Deane, is traditionally cultivated as an edible/medicinal crop in East Asia. Its essential oil contains many bioactive compounds that are expected to have high pharmacological functionality, as well as antimicrobial and insecticidal activity. Spider mites are a major pest group for perilla cultivation. The two-spotted spider mite, Tetranychus urticae Koch, possesses divergent detoxification enzymes and has developed resistance against most acaricides. The essential oil content of perilla halves from the pre-flowering phase to the flowering phase, and ultraviolet (UV)-B radiation generally increases defense compounds. To clarify the effects of this change in essential oil content and the effects of UV-B pretreatment, we investigated the developmental success and egg production of T. urticae on leaves from the preflowering and flowering phases cultivated with and without nighttime UV-B irradiation. Both the parameters significantly increased on leaves from the flowering phase in comparison with that from the preflowering phase, suggesting that constitutively produced essential oil provided protection against mite pests in a growth phase-specific manner. The defense system also extended the developmental period of mites on red perilla leaves, but not on green perilla leaves, in preflowering phase. Although egg production was lower on red perilla leaves pretreated with UV-B, no negative effects were caused on the developmental success and duration on red and green perilla and the egg production on green perilla by UV-B pretreatment. Our findings reveal a significant impact of investment allocation of perilla plants and a small contribution of UV-B irradiation to the plant defense system.

Dose-Response and Temperature Dependence of the Mortality of Spider Mite and Predatory Mite Eggs Caused by Daily Nighttime Ultraviolet-B Irradiation

The two-spotted spider mite, Tetranychus urticae, is an economically important agricultural pest. A novel physical control method involving daily nighttime UV-B irradiation was recently developed for use in strawberry greenhouses. However, the overlapping of leaves after March prevents direct irradiation to T. urticae on the lower leaf surface, decreasing control effect. Excessive UV-B irradiation causes leaf sunscald in winter. Therefore, optimization of UV-B irradiance and a compensatory control agent are desired. Temperature may affect the survival of organisms exposed to UV-B, although the temperature dependence of UV-B damage is controversial. A phytoseiid mite, Neoseiulus californicus, is a prominent predator but vulnerable to a single UV-B irradiation. We compared dose-response and temperature dependence of UV-B damage between T. urticae and N. californicus eggs under daily nighttime UV-B irradiation. Unexpectedly, N. californicus showed greater resistance to UV-B than T. urticae, and the mortality was increased and decreased at low and high temperatures, respectively. This makes possible the application of UV-B doses that are lethal for spider mites but safe for phytoseiid mites. Overall, we concluded that combined use of phytoseiid mites with UV-B lamps is advantageous to spider mite management in strawberry greenhouses.