Influence of abiotic factors on diapause termination and temperature requirements for postdiapause development in the European red mite, Panonychus ulmi (Acari: Tetranychidae).

The European red mite Panonychus ulmi (Koch) is widely distributed and it can severely affect pome fruit crops, particularly apple. Pest outbreaks are related to an overuse of non-selective pesticide treatments that lead to the development of resistance and the absence of natural enemies in the orchard. A key aspect to optimize the use of pesticide treatments in the context of IPM is to increase the knowledge on the biology and ecology of the pest to better predict population dynamics and outbreaks. For the European red mite, knowledge on the conditions that lead to diapause breaking by winter eggs is essential to model population dynamics. To increase this knowledge, winter eggs were collected during field surveys in northen Spain during three years and egg hatching was monitored under controlled temperature and photoperiod conditions in the laboratory. The "number of days exposed to cold temperatures" was the most significant factor that positively affected hatching of overwintering eggs. The time required for 50% of the egg population to hatch (T50%) was also negatively modulated by the duration of exposure to cold temperature. The temperature threshold for postdiapause eggs development collected from the field was estimated between 5 and 6 ºC in 2005 and 2007, respectively. Moreover, the degree-days required for post diapause development were estimated between 263.2 and 270.3, depending on the year of collection. Collectively, we provide additional information on the diapause termination and postdiapause development of the European red mite that may effectively contribute to optimize pest population models.

Prey stage preference of Amblyseius paraaerialis (Acari: Phytoseiidae) on varied life stages of the spider mites Tetranychus urticae, Tetranychus macfarlanei and Oligonychus biharensis (Acari: Tetranychidae) and exploring the mass rearing possibilities of this predatory mite on alternative diets.

Spider mites Tetranychus urticae, Tetranychus macfarlanei and Oligonychus biharensis are considered to be highly polyphagous in nature and causes severe damage to a wide range of plants around the world. Amblyseius paraaerialis is an efficient phytoseiid predator of spider mites with a potential to survive on both natural and alternative diets. Evaluation of predatory potential and prey stage preference provides valuable information on the efficacy of the predatory species in controlling mite population. Feeding experiments were conducted on mulberry leaf discs under the laboratory conditions of 30 ± 2 °C and 70 ± 5% relative humidity (RH). After 24 h of feeding experiment, the adult female predator exhibited a significant preference in feeding towards the eggs of T. macfarlanei (42.6%) and the larval stages of T. urticae (46%) and O. biharensis (25.3%). The mass rearing possibilities of A. paraaerialis was tested by tracking and comparing the developmental duration of individual life stages on varied food sources like, honey, castor (Ricinus communis) pollen, honey-pollen mixture and mixed life stages of T. urticae. The predator was failed to complete its development on honey and pollen when supplied separately. However it was successfully developed on honey-pollen mixture and mixed life stages of T. urticae. The developmental studies unravelled a shortest developmental duration and an extended adult longevity and lifespan of A. paraaerialis when reared on the alternative diet, thus opened up the mass rearing possibility of the predatory species under laboratory conditions.

An exploratory analysis of the structure of tetranychid and phytoseiid assemblages in walnut orchards in California.

Spider mites were considered secondary pests of walnut production in California, under the control of phytoseiid predators. Due to increased importance as walnut pests in recent decades there is renewed interest in the structure and function of the associated phytoseiid assemblage. In this study we report the results from a 3 year survey of the tetranychid and phytoseiid assemblages in walnut orchards in the Central Valley of California. The survey was conducted to determine the range and dominance of web-spinning Tetranychus species present, to investigate the species richness and dominance of the phytoseiid species present, and to explore whether patterns of variation in the relative abundance of phytoseiid species could be explained by one or more explanatory variables. Tetranychus urticae was the dominant spider mite in all growing regions and years with T. pacificus and T. turkestani also present in orchards in the southern San Joaquin Valley. Phytoseiid species richness declined with latitude among the three walnut growing regions and of the 13 species found Amblyseius similoides, Euseius stipulatus, Galendromus occidentalis and Typhlodromus caudiglans were the most abundant and widespread species present. Mean proportional abundance significantly increased from early (mid May-July) to late (August-mid October) season and from southern to northern growing regions for Type II and IV predators, but significantly decreased from early to late season and from southern to northern growing regions for Type III predators. The mean proportional abundance of Type II predators, particularly G. occidentalis, significantly increased and that of Type III predators significantly decreased with mean Tetranychus density in individual orchards. The current survey provides a more in-depth analysis of mite assemblages in walnut orchards in California and can be used to better inform adaptive management strategies for integrated mite management in the future.

Herbivore-induced plant volatiles emitted by citrus in response to spider mite infestation can attract predatory mites.

Understanding the nutritional interplay among plants, pests, and natural enemies is essential for sustainable pest management. Enhancing the efficiency of natural enemies, such as Neoseiulus californicus (McGregor) (Acari: Phytoseiidae) is critical, and exploiting herbivore-induced plant volatiles (HIPVs) offers a promising approach. However, N. californicus has rarely been reported to utilize HIPVs to improve their biological control capabilities. Our research revealed a significant difference in the diversity of volatile compounds detected in clean Citrus reticulata Blanco leaves compared to those in C. reticulata leaves infested with Panonychus citri (McGregor) (Acari: Tetranychidae), regardless of mite presence. This suggests that P. citri infestation induces a wide array of HIPVs in C. reticulata leaves. We conducted olfactory behavioral assays to evaluate the response of N. californicus to synthetic HIPVs. Results revealed that linalool (1.00 mg/mL), 2,2,4-trimethylpentane (10.0 mg/mL), undecylcyclohexane (1.00 mg/mL), and (+)-dibenzoyl-L-tartaric anhydride (10.0 mg/mL) significantly attracted N. californicus while pentadecanal (1.00 mg/mL) significantly deterred it. A 3-component blend of linalool, undecylcyclohexane, and (+)-dibenzoyl-L-tartaric anhydride was better than other combinations in attracting N. californicus. This combination provided the basis for developing an attractant for N. californicus, facilitating the rate of its dispersal to enhance its biological control of pests. Consequently, this research offers vital insights into improving the sustainable pest control potential of predatory mites.

A new spider mite elicitor triggers plant defence and promotes resistance to herbivores.

Herbivore-associated elicitors (HAEs) are active molecules produced by herbivorous insects. Recognition of HAEs by plants induces defence that resist herbivore attacks. We previously demonstrated that the tomato red spider mite Tetranychus evansi triggered defence in Nicotiana benthamiana. However, our knowledge of HAEs from T. evansi remains limited. Here, we characterize a novel HAE, Te16, from T. evansi and dissect its function in mite-plant interactions. We investigate the effects of Te16 on spider mites and plants by heterologous expression, virus-induced gene silencing assay, and RNA interference. Te16 induces cell death, reactive oxygen species (ROS) accumulation, callose deposition, and jasmonate (JA)-related responses in N. benthamiana leaves. Te16-mediated cell death requires a calcium signalling pathway, cytoplasmic localization, the plant co-receptor BAK1, and the signalling components SGT1 and HSP90. The active region of Te16-induced cell death is located at amino acids 114-293. Moreover, silencing Te16 gene in T. evansi reduces spider mite survival and hatchability, but expressing Te16 in N. benthamiana leaves enhances plant resistance to herbivores. Finally, Te16 gene is specific to Tetranychidae species and is highly conserved in activating plant immunity. Our findings reveal a novel salivary protein produced by spider mites that elicits plant defence and resistance to insects, providing valuable clues for pest management.

Combined nighttime ultraviolet B irradiation and phytoseiid mite application provide optimal control of the spider mite Tetranychus urticae on greenhouse strawberry plants.

BACKGROUND: Tetranychus urticae is a hard-to-control pest of greenhouse strawberry production. Nighttime ultraviolet B (UV-B) radiation using light reflection sheets (LRS) has been applied as a physical method to control T. urticae through direct ovicidal effects (the UV method). However, because strawberry leaves grow more densely, UV-B radiation fails to reach the lower leaf surfaces inhabited by spider mites; therefore, a complementary method is required. We propose the supplemental application of phytoseiid mites in greenhouse strawberry production. We evaluated the control effects of UV-B irradiation, phytoseiid mite application and their combined use. The effects of UV-B irradiation on the degree of overlap relative to the independent distributions (ω) between predators and prey were also analyzed. RESULTS: The UV method alone maintained low T. urticae density levels from November to February; however, mite populations increased from March onward. Phytoseiid mite application in January and February without UV-B irradiation resulted in a temporary increase in spider mites in March and/or April. By contrast, combined application of the UV method and phytoseiid mites had a greater control effect during the strawberry growing season. The ω values were higher for the UV method compared with no UV-B irradiation, suggesting that UV-B irradiation increased phytoseiid mite foraging rates. CONCLUSION: The release of phytoseiid mites compensated for the shortcomings of the UV method, and UV-B irradiation promoted predation by phytoseiid mites by increasing the behavioral numerical response. Consequently, combined application of UV-B irradiation and phytoseiid mites is optimal for T. urticae control in greenhouse strawberry production. © 2023 Society of Chemical Industry.

Functional response of Neoseiulus californicus (Acari: Phytoseiidae) to Tetranychus urticae (Acari: Tetranychidae) at different temperatures.

Environmental factors like temperature have a great impact on the predation potential of biological control agents. In the present study, the functional response of the predatory mite Neoseiulus californicus (Acari: Phytoseiidae) to the pest mite Tetranychus urticae (Acari: Tetranychidae) at moderate to high temperatures under laboratory conditions was determined. The study aimed to understand the prey-predator interaction under different temperatures and prey densities. Five constant temperatures (24 °C, 27 °C, 30 °C, 33 °C, and 36 °C), and thirteen prey densities (4, 5, 8, 10, 12, 15, 16, 20, 24, 25, 30, 32, and 40) of each stage (adult, nymph, larvae, and egg stage) were employed in the experiment. Observations were made 24 h after the start of each experiment. Results revealed that the predatory mites showed type II functional response to adult females of T. urticae, whereas type I to other stages (nymphs, larvae, and eggs) of T. urticae. The predation capability of adult predatory mites on T. urticae was significant at 24-36 °C. The instantaneous attack rate (a) of N. californicus increased and the handling time (Th) decreased with an increase in temperature. The maximum attack rate was recorded at 36 °C (1.28) for the egg stage. The longest handling time was (0.78) for the larval stage of T. urticae at 30 °C. Daily consumption increased with increasing prey density. Maximum daily consumption was observed at 33 °C (30.00) at the prey density of 40. Searching efficiency decreased with the increase in prey density but was found to increase with the rise in temperature. N. californicus was found to be voracious on the larval and egg stages. Conclusively, the incorporation of N. californicus at earlier stages (larvae and eggs) of T. urticae would be beneficial under warm conditions because managing a pest at its initial stage will save the crop from major losses. The results presented in this study at various temperatures will be helpful in different areas with different temperature extremes. The results of the functional response can also be applied to mass rearing, quality testing, and integrated pest management programmes.

Sperm-depleted males of the two-spotted spider mite can replenish sperm in a few hours.

In many animals, males increase their reproductive success by mating with as many females as possible. The number of females a male can fertilize is often limited by male competition for access to females, sperm competition, and the cost of sperm production. Especially, recent studies have shown that sperm production is more costly than previously expected. In the two-spotted spider mite, Tetranychus urticae Koch, the number of females a male can inseminate is limited mainly by male competition for access to females. However, in the absence of rivals, males mate with so many females that they can become sperm-depleted. Mating without sperm transfer does not produce any offspring, although it takes time and energy. Therefore, a question arises as to why males continue to mate even after sperm depletion. In this study, we hypothesized that males continue to mate because sperm is replenished after a short period. To test the hypothesis, we investigated how long it takes for sperm replenishment after sperm depletion. We found that in 3 h, sperm can be replenished enough to inseminate a few females. As 3 h is sufficiently short not to lose the next mating opportunity, the results support the hypothesis. However, copulation duration in the sperm-replenished males was significantly longer than in the sperm-depleted males but shorter than in males before sperm depletion. To explain the differences, further research would be necessary. In addition, anatomical physiology study in males is also required to confirm that sperm is indeed depleted and replenished.

Is there a downside to plant ecological services in the city? Influences of particulate matter on the two-spotted spider mite (Tetranychus urticae) foraging on the small-leaved lime in urban conditions.

The aim of this research was to examine how particulate matter (PM) pollution affects the life history of the two-spotted spider mite (TSSM), Tetranychus urticae (Trombidiformes: Tetranychidae), in modelled urban conditions. For this purpose, experimental populations of TSSM were cultured on the foliage of small-leaved lime (Tilia cordata) contaminated with PM at intensities corresponding to differing city zones such as a park, a busy road and an industrial area. The control samples in the study were washed, unpolluted leaves. The spider mite was selected as a model organism due to its cosmopolitan distribution, broad host spectrum, resistance to a variety of pesticides and food-intake mode involving cell-content sucking, while T. cordata is widely planted in cities and has demonstrated a considerable capability for PM capture. Data on the longevity and mortality of particular instars and on female fecundity at different pollution levels were collected and statistically evaluated. Concentrations of PM typical for roads and industrial city zones significantly reduced total female fecundity (avg. 53.9 and 55.9 eggs/female, respectively, vs 79.2 in control), which entailed a slower population increase, while the survival rate of particular developmental instars (P = 0.52) and fertility curves (P = 0.19) remained unchanged. The presence of PM caused physiological effects in the mites, despite the lack of direct consumption of the pollutant by adult and juvenile instars. Considering the incomparable resilience of TSSM to unfavourable environmental factors, it is predicted that the detrimental influence of PM on other representatives of urban arthropods may be even more severe. The results suggest that there is a need for further investigations into the ecological ramifications of air purification provided by urban green spaces.

Presence of nontarget prey, Tetranychus truncatus, affected the predation by Neoseiulus bicaudus on Tetranychus turkestani.

Neoseiulus bicaudus (Wainstein) (Acari: Phytoseiidae) is a generalist predatory mite that consumes several pest species, including Tetranychus turkestani (Ugarov et Nikolskii) (Acari: Tetranychidae) in the Xinjiang Uygur Autonomous Region. The release numbers of predatory mites are based on the populations of target pests and their ability to control them. Populations of T. turkestani and T. truncatus Ehara (Acari: Tetranychidae) often coexist and damage many crops. To determine whether the presence of the non-target prey T. truncatus affects the ability of N. bicaudus to control the target prey T. turkestani. The study evaluated the predation rate and functional response of N. bicaudus to 4 stages of T. turkestani in the presence of T. truncatus. The consumption of T. turkestani by N. bicaudus gradually decreased as the proportion of T. truncatus increased. The functional response of N. bicaudus to T. turkestani was not changed when T. truncatus was presented, which was consistent with a type II response. The attack rate of N. bicaudus on the egg, larva, and nymph of T. turkestani was significantly decreased and the handling time of N. bicaudus on T. turkestani was significantly extended when T. truncatus was presented. The preference index showed that the preference of N. bicaudus for eggs and female adults of T. turkestani decreased with increasing density of T. turkestani in the same proportion as T. truncatus. The presence of T. truncatus can negatively affect the predation of T. turkestani by N. bicaudus. We suggest that the number of N. bicaudus released to control T. turkestani should be increased when T. truncatus coexist.

Tissue-specific regulation of volatile emissions moves predators from flowers to attacked leaves.

Plant-predator mutualisms have been widely described in nature.1,2 How plants fine-tune their mutualistic interactions with the predators they recruit remains poorly understood. In the wild potato (Solanum kurtzianum), predatory mites, Neoseiulus californicus, are recruited to flowers of undamaged plants but rapidly move downward when the herbivorous mites, Tetranychus urticae, damage leaves. This "up-down" movement within the plant corresponds to the shift of N. californicus from palynivory to carnivory, as they change from feeding on pollen to herbivores when moving between different plant organs. This up-down movement of N. californicus is mediated by the organ-specific emissions of volatile organic compounds (VOCs) in flowers and herbivory-elicited leaves. Experiments with exogenous applications, biosynthetic inhibitors, and transient RNAi revealed that salicylic acid and jasmonic acid signaling in flowers and leaves mediates both the changes in VOC emissions and the up-down movement of N. californicus. This alternating communication between flowers and leaves mediated by organ-specific VOC emissions was also found in a cultivated variety of potato, suggesting the agronomic potential of using flowers as reservoirs of natural enemies in the control of potato pests.

Expression and functional analysis of Niemann-Pick C2 gene in Phytoseiulus persimilis.

As a new protein class of semiochemical binding and transporting, Niemann-Pick proteins type C2 (NPC2) in arthropods have received more attentions in recent decade. However, the gene function has not been studied in phytoseiid mites with biocontrol potential. In the current study, we cloned a NPC2 gene PpNPC2a from the transcriptome of Phytoseiulus persimilis Athias-Henriot. By encoding 181 amino acids with a conserved ML domain, PpNPC2a was found a homolog of NPC2-1 in Galendromus occidentalis Nesbitt. We then measured the spatio-temporal expression of PpNPC2a in P. persimilis, and found the highest expression in female adults compared to other stages. Due to the tiny body size of predatory mites, we only examined tissue expressions in two sections: the anterior part (gnathosoma and the first pair of legs) and the posterior part (idiosoma without the first pair of legs). Higher transcription of PpNPC2a was found in the posterior part. To investigate the potential function of PpNPC2a in P. persimilis, we interfered gene expression in female adults by feeding dsRNA, which resulted in a decrease of relative expression by 59.1 and 78.2% after 24 and 72 h, respectively. Compared with the control, dsNPC2a-treated P. persimilis were insensitive to the scent of leaves or plants infested by spider mites, suggesting a role of PpNPC2a in response to plant volatiles. However, the dsNPC2a-interfered mites could still respond to four representative compounds of herbivore-induced plant volatiles, including 4,8,12-trimethyl-1,3,7,11-tridecatetraene (TMTT), methyl salicylate (MeSA), ß-caryophyllene and linalool. In short, our results indicated PpNPC2a may be involved in the chemosensory process of P. persimilis in response to whole-plant volatiles.

Exogenous methyl jasmonate induced cassava defense response and enhanced resistance to Tetranychus urticae.

Exogenous application of methyl jasmonate (MeJA) could activate plant defense response against the two-spotted spider mite (TSSM), Tetranychus urticae Koch, in different plants. However, whether MeJA can also serve as an elicitor in cassava (Manihot esculenta Crantz) remains unknown. In this study, induced defense responses were investigated in TSSM-resistant cassava variety C1115 and TSSM-susceptible cassava variety KU50 when applied with MeJA. The performance of TSSM feeding on cassava plants that were pre-treated with various concentrations of MeJA was first evaluated. Subsequently, the activities of antioxidative enzymes (superoxide dismutase and catalase), detoxification enzymes (glutathione S-transferase, cytochrome P450 and carboxylesterase) and digestive enzymes (protease, amylase and invertase) in TSSM were analyzed at days 1, 2, 4 and 8 post-feeding. The results showed that MeJA treatment can induce cassava defense responses to TSSM in terms of reducing egg production and adult longevity as well as slowing development and prolonging the egg stage. Noticeably, C1115 exhibited stronger inhibition of TSSM development and reproduction than KU50. In addition, the activities of all the tested enzymes were induced in both C1115 and KU50, the most in C1115. We conclude that exogenous methyl jasmonate can induce cassava defense responses and enhance resistance to TSSM.

Rapid cold hardening response of the phytoseiid mite Neoseiulus striatus: increased cold tolerance but not reduced predation.

The predatory mite Neoseiulus striatus (Wu) (Acari: Phytoseiidae), which has been found on maize plants in Inner Mongolia, is regarded as a promising biological control agent of small sucking pests, especially Tetranychid mites. Temperature is an important abiotic factor, and a sudden drop in temperature may affect its performance when released in areas with big circadian temperature differences. Rapid cold hardening is a type of phenotypic plasticity that allows ectotherms to quickly enhance their cold tolerance in response to a brief chilling exposure. However, it is not clear whether N. striatus possesses such plasticity. To understand how this species of phytoseiid mite copes with short-term low-temperature stress, its rapid cold hardening response was studied in the laboratory by first exploring its critical temperature. Then, the effects of exposure to a series of temperatures (0, 5, 10, 15, and 20 °C) for different durations on the survival of N. striatus were investigated to determine the optimal temperature and duration for cold hardening. Moreover, the effect of cold hardening on the consumption of Tetranychus urticae by N. striatus was also investigated, as was the response of immature stages. The critical temperature for N. striatus was - 15 °C, at which its survival dropped below 10%. An exposure to 5 °C for 2 h was optimal for rapid cold hardening, efficiently increasing survival in N. striatus. Rapid cold hardening was found in all developmental stages of N. striatus, and there was no significant effect of exposure on the consumption of spider mites. Our study shows that exposure to low temperatures during a limited period can enhance the cold hardiness but not reduce predation by N. striatus, which will be advantageous to its field applications during a period of large diurnal temperature fluctuations.

A conserved protein disulfide isomerase enhances plant resistance against herbivores.

Herbivore-associated molecular patterns (HAMPs) enable plants to recognize herbivores and may help plants adjust their defense responses. Here, we report on herbivore-induced changes in a protein disulfide isomerase (PDI) widely distributed across arthropods. PDI from the spider mite Tetranychus evansi (TePDI), a mesophyll-feeding agricultural pest worldwide, triggered immunity in multiple Solanaceae plants. TePDI-mediated cell death in Nicotiana benthamiana required the plant signaling proteins SGT1 (suppressor of the G2 allele of skp1) and HSP90 (heat shock protein 90), but was suppressed by spider mite effectors Te28 and Te84. Moreover, PDIs from phylogenetically distinct herbivorous and nonherbivorous arthropods triggered plant immunity. Finally, although PDI-induced plant defenses impaired the performance of spider mites on plants, RNAi experiments revealed that PDI genes are essential for the survival of mites and whiteflies. Our findings indicate that plants recognize evolutionarily conserved HAMPs to activate plant defense and resist pest damage, pointing to opportunities for broad-spectrum pest management.

Temperature-dependent Functional Response of the Arboreal Rove Beetle, Oligota flavicornis (Coleoptera: Staphylinidae), a Voracious Predator of Tetranychus urticae (Acarina: Tetranychidae).

The functional responses of Oligota flavicornis (Boisduval & Lacordaire) (Coleoptera: Staphylinidae) preying on the eggs of Tetranychus urticae Koch (Acarina: Tetranychidae) were examined at seven constant temperature settings (12, 15, 18, 22, 25, 30, and 32°C) to elucidate the predator-prey interactions between them. Logistic regression showed that O. flavicornis exhibited type II functional responses to T. urticae eggs at different temperatures. The reciprocal of handling time declined exponentially with warming, and the search rate presented a single hump-shaped relationship with temperature. For the search rate, the lower temperature thresholds were 9.1°C (linear) and 8.7°C (Briere). The optimal temperature and upper temperature threshold were 29.1 and 37.8°C for Logan and 29.7 and 35.8°C for Briere, respectively. The predation threshold window of O. flavicornis reached 27.1°C with a range of 8.7-35.8°C. The predator could consume 244.7-388.4 T. urticae eggs in a day in the optimal temperature range (18-32°C). The voracious predatory behavior of O. flavicornis against T. urticae eggs over a broad temperature range indicates that the predator shows promise as a potential biological control agent and that temperature-dependent predation could be a basis for formulating strategies to control tetranychid mites.

Potential of UV-C for management of two-spotted spider mites and thrips in Florida strawberry.

BACKGROUND: Major pests of Florida strawberry (two-spotted spider mites, Tetranychus urticae Koch; chilli thrips, Scirtothrips dorsalis Hood; and western flower thrips, Frankliniella occidentalis Pergande) are difficult to manage using only conventional chemical control. Previous research has demonstrated high mortality of T. urticae eggs after exposure to ultraviolet B (UV-B) light. Additionally, ultraviolet C (UV-C) light has been shown to suppress powdery mildew in strawberry at doses between 85 and 200 J m-2 with no damage to the plant. Therefore, UV-C may also have the potential to be used as an integrated pest management tool for arthropod pests of strawberry. The objectives of this study were to: (i) determine the effect of UV-C on T. urticae, S. dorsalis, and F. occidentalis natural populations in open-field strawberry; and (ii) determine the effect of UV-C on T. urticae egg hatch after application in open-field strawberry. Field studies were conducted during the 2019-2020 and 2020-2021 strawberry seasons in Florida, USA. Four treatments were compared: (i) foliar application of spinetoram in response to natural pest pressure; (ii) application of UV-C 200 J m-2 twice a week; (iii) application of UV-C 350 J m-2 twice a week; and (iv) a non-treated control. RESULTS: In the field trials, suppression of T. urticae was observed at 350 J m-2 in 2020-2021. In the other field trials, no effect was observed due to low natural infestations. No negative impact on yield was observed from UV-C applications. CONCLUSION: UV-C shows promise as a component of an integrated pest management program for T. urticae in strawberry. © 2022 Society of Chemical Industry.

The Microbiota of a Mite Prey-Predator System on Different Host Plants Are Characterized by Dysbiosis and Potential Functional Redundancy.

Microbiota has diverse roles in the life cycles of their hosts, affecting their growth, development, behavior, and reproduction. Changes in physiological conditions of the host can also impact the assemblage of host-associated microorganisms. However, little is known of the effects of host plant-prey-predatory mite interactions on mite microbiota. We compared the microbial communities of eggs and adult females of the two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), and of adult females of the predatory mite Neoseiulus californicus (McGregor) (Acari: Phytoseiidae) on four different host plants (cotton, maize, pinto bean, and tomato) by metabarcoding sequencing of the V3-V4 region of the 16S ribosomal RNA gene (16S rRNA), using the Illumina MiSeq platform. Only the egg microbiota of T. urticae was affected by the host plant. The microbiota of the predatory mite N. californicus was very different from that of its prey, and the predator microbiota was unaffected by the different host plant-prey systems tested. Only the microbiota of the eggs of T. urticae carried Serratia as a high fidelity-biomarker, but their low abundance in T. urticae adult females suggests that the association between Serratia and T. urticae is accidental. Biomarker bacteria were also detected in the microbiota of adult females of T. urticae and N. californicus, with different biomarkers in each host plant species. The microbiota associated with eggs and adult females of T. urticae and adult females of N. californicus differed in their functional potential contributions to the host mite.

Predator- and killed prey-induced fears bear significant cost to an invasive spider mite: Implications in pest management.

BACKGROUND: The success of biological control using predators is normally assumed to be achieved through direct predation. Yet it is largely unknown how the predator- and killed prey-induced stress to prey may contribute to biological control effectiveness. Here, we investigate variations in life-history traits and offspring fitness of the spider mite Tetranychus ludeni in response to cues from the predatory mite Phytoseiulus persimilis and killed T. ludeni, providing knowledge for evaluation of the nonconsumptive contribution to the biological control of T. ludeni and for future development of novel spider mite control measures using these cues. RESULTS: Cues from predators and killed prey shortened longevity by 23-25% and oviposition period by 35-40%, and reduced fecundity by 31-37% in T. ludeni females. These cues significantly reduced the intrinsic rate of increase (rm ) and net population growth rate (R0 ), and extended time to double the population size (Dt ). Predator cues significantly delayed lifetime production of daughters. Mothers exposed to predator cues laid significantly smaller eggs and their offspring developed significantly more slowly but these eggs had significantly higher hatch rate. CONCLUSION: Predator- and killed prey-induced fears significantly lower the fitness of T. ludeni, suggesting that these nonconsumptive effects can contribute to the effectiveness of biological control to a great extent. Our study provides critical information for evaluation of biological control effectiveness using predators and paves the way for identification of chemical odors from the predator and killed prey, and development of new materials and methods for the control of spider mite pests. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

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.