Spider Mite Eggs Research Articles

Effect of Methyl Jasmonate on the Performance of Tetranychus evansi Baker & Pritchard, 1960 (Acari: Tetranychidae) and Phytoseiulus longipes Evans, 1968 (Acari: Phytoseiidae) on Tomato Plants

Inducible anti-herbivore defenses in plants are predominantly regulated by jasmonic acid (JA). The red spider mite Tetranychus evansi Baker & Pritchard, 1960 (Acari: Tetranychidae) is an invasive pest known for its detrimental impact on tomato plants and other Solanaceae crops. Here, we investigated the extent to which T. evansi and the predatory mite Phytoseiulus longipes Evans, 1968 (Acari: Phytoseiidae) are affected by induced JA-defenses. Initially, we artificially induced the JA-response in tomato plants using exogenous methyl jasmonate (MeJA) and subsequently assessed the effect of JA defenses on spider mite by evaluating mortality and oviposition rates. Our findings revealed a higher mortality and lower oviposition rates on plants treated with MeJA compared to non-treated control plants. Furthermore, we examined the predatory mite's predation rates on spider mite eggs produced on MeJA-treated and non-treated tomato plants. The results showed a reduced predation on T. evansi eggs derived from MeJA-treated plants, indicating a potential negative impact of JA-induced defenses on the predator's performance. Finally, we released five predatory females on T. evansi-infested tomato plants treated and non-treated with MeJA, monitoring the predator population density for three generations. Predator population was not affected, as the abundance of larvae and adults was not significantly different between treatments. These findings underscore the negative impact of JA defenses on herbivores and highlight the trade-off it may pose on natural enemies.

Contact Toxicity of an Essential Oil from Acorus calamus (Acoraceae) Rhizomes against Tetranychus urticae and Tetranychus macfarlanei (Acari: Tetranychidae) and Amblyseius longispinosus (Acari: Phytoseiidae)

Abstract The contact toxicity activity of an essential oil extracted from Acorus calamus (L.) (Acoraceae) was evaluated against the phytophagous spider mites Tetranychus urticae Koch and Tetranychus macfarlanei Baker & Pritchard (Acari: Tetranychidae) and the predatory mite Amblyseius longispinosus (Evans) (Acari: Phytoseiidae). Adult mortality 24 h following application of 5% (v/v) concentration of the essential oil exceeded 90% for T. urticae and T. macfarlanei. Application of 1.2–5% concentrations of the essential oil to mite eggs reduced egg viability, with 0–54% hatch of T. urticae eggs and 0% hatch of T. macfarlanei eggs 6 d following treatment. At 2.5%, the essential oil was toxic to A. longipinosus by residual contact toxicity (58% mortality) and direct contact toxicity (0% mortality). No eggs and 47.6 eggs of A. longispinosus were oviposited with residual contact toxicity and direct contact toxicity, respectively. The chemical constituents of the essential oil, as determined with gas chromatography–mass spectrometry, showed that camphor (41.07%) and 5,5-dimethyl-2-ethynylcyclopent-2-en-1-ol (27.96%) were the major chemical compounds of the essential oil. These results indicate that this essential oil extracted from fresh A. calamus rhizomes could prove useful in controlling T. urticae and T. macfarlanei. Our findings also showed that the essential oil had no deleterious effects against A. longispinosus by direct contact toxicity test; however, A. longispinosus consuming spider mite eggs treated with essential oil were negatively impacted.

Development, survival, and reproduction of Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseiidae) feeding on fresh versus frozen eggs of Tetranychus urticae Koch (Acari: Tetranychidae)

Phytoseiulus persimilis Athias-Henriot is an important biocontrol agent for controlling spider mites (Tetranychus spp). Rearing P. persimilis is relatively expensive due to the need to raise spider mites (e.g. Tetranychus urticae Koch), as prey, on live plants. Frozen eggs of T. urticae can be easily stored and used as a potential feed for laboratory rearing of P. persimilis. This study investigated the performance of frozen T. urticae eggs compared with fresh eggs as food for rearing P. persimilis. Under laboratory conditions, the survival, immature development, consumption, and oviposition of P. persimilis given frozen or fresh T. urticae eggs were observed. The influence of the dietary experience of P. persimilis females (i.e. fed on frozen or fresh spider mite eggs) on offspring’s development and consumption was also examined. The survival and development of P. persimilis were not affected by the different diets. However, individuals fed on frozen T. urticae eggs had a reduced oviposition rate and an increased consumption compared with those given fresh eggs. The maternal dietary experience did not affect the development and consumption of P. persimilis. As the nutritional quality of T. urticae eggs is likely reduced during freezing, the frozen eggs of T. urticae may be inadequate compared with fresh eggs in rearing P. persimilis. Nevertheless, frozen eggs have the potential as supplementary food for P. persimilis. Future studies can investigate the performance of frozen T. urticae eggs on the lifespan and lifetime fecundity and in maintaining a population of P. persimilis in the field.

Molecular gut-content analysis in phytoseiid mites

Molecular gut content analysis has been used widely to elucidate predator-prey interaction both in natural and agricultural ecosystems. The two-spotted spider mites, Tetranychus urticae (Acari: Tetranychidae), is one of the most important pest species worldwide, mainly due to their acaricide resistance. In greenhouses, commercially available biological control agents (BCAs), such as Phytoseiiulus persimilis and Neoseiulus californicus (Acari: Phytoseiidae), have been used. However, in open fields like orchards, conservation biological control (CBC) is desirable rather than augmentation, because natural populations of phytoseiid mites, which can potentially control spider mites, are distributed. There can be several species of phytoseiid mites feeding on spider mites in the same habitat, and therefore it is important to know which species can control spider mites effectively. To this end, Hinomoto (2017) elucidated the effectiveness of molecular gut-content analysis in the predatory mite, N. californicus, and showed that ordinary agarose gel electrophoresis of PCR products could not detect any bands, but fluorescent-labeled primers successfully detected the gut contents of phytoseiid mites and confirmed they were derived from spider mite eggs. Furthermore, he also found that newly deposited spider mite eggs (less than 3 hr of oviposition) consumed by the predatory mites could not be detected even if fluorescent-labeled primers were used. To apply this technique in the fields, this should be carefully taken in the consideration, although it is unknown whether old or new eggs of spider mites are preferred. Regardless of this phenomenon, a combination of barcoding of phytoseiid mite species and molecular cut-content analysis will reveal real predator-prey food web in fields.

FRUIT TREES MCDANIEL SPIDER MITE

The article аlthough the McDaniel spider mite is less polyphagous than the two spotted spider mite, its host range is nevertheless rather diverse. It turns a dull ivory hue just before hatching, and the embryo's crimson eyespots are evident. McDaniel spider mite eggs and two spotted spider mite eggs are indistinguishable. The estimate of mites per leaf is calculated by dividing the total number of mites on the plate by the number of leaves brushed onto that plate

Prey requirement and development of a predatory mite under diet restriction: Phytoseiulus persimilis Athias-Henriot (Phytoseiidae) feeding on Tetranychus urticae Koch (Tetranychidae)

Phenotypic plasticity is a mechanism where different phenotypes are expressed from a genotype allowing individuals to survive variable environments. Diet-induced phenotypic plasticity was observed in the developmental time and size at maturity of the specialist predatory mite Phytoseiulus persimilis. As a preliminary study, we investigated variations in developmental time and size at maturity of P. persimilis under intermediate diet restriction of 10 and 20 spider mite (Tetranychus urticae) eggs using enclosed rearing cells. Analysis of covariance using consumption as a covariate showed no difference in the developmental time of P. persimilis between the different prey densities. Additionally, the size at maturity of P. persimilis given different prey densities was similar from the Wilcoxon rank sum test. However, when given 20 prey eggs, a relatively high variation was found in the consumption rate of both female and male P. persimilis. The findings of this study are essential for designing our later studies on the influence of diet restriction and lifespan of P. persimilis. This study also expands our understanding of the viability and adaptability of P. persimilis under food stress.

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

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. 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. 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.

Influence of Alternative Food Sources on Different Biological Aspects of Cydnoseius negevi (Acari: Phytoseiidae) تأثير مصادر الغذاء البديلة على النواحي البيولوجيه المختلفه للمفترس الأکاروسي Cydnoseius Negevi (Acari: Phytoseiidae)

The predatory mite Cydnoseius negevi (Swirski & Amitai), (Family Phytosidae), is a predaceous mite of different mite and insect pests, such as two-spotted spider mite and castor whitefly. This work aimed to study the role of C. negeviin controlling the four arthropod pests, Spodoptera littoralis (Boisduval), Trialeurodes ricini (Misra), and Anagasta (Ephestia) kuehniella (Keller) as wellas spider mite Tetranychus urtica (Koch) compared with date palm pollenas food options under controlled conditions. The predatory mite C. negevican feed and complete its life span successfully on these foods. Trialeurodes ricini and A. kuehniella eggs prolonged the life cycle of C. negevi. Likewise, the shortest period observed when male and female fed on eggs of T. urtica. Egg production of the tested mite was the highest when it fed on pollen, while oviposition was lower when the predatory mite fed on T. ricini. Food sources also affected all life tables where spider mite eggs and pollen grains were the most favorable foods increased Ro, rm, erm and GRR values. Insect eggs prolonged T and Dt times ofthe tested mite C. negevi. Therefore, C. negevi could be reared successfully on date palm pollen and eggs of S. littoralis, T. ricini, A. kuehniella and T. urticae.

Oviposition-site shift in phytophagous mites reflects a trade-off between predator avoidance and rainstorm resistance.

Predators can reduce prey population densities by driving them to undertake costly defences. Here, we report on a remarkable example of induced antipredator defence in spider mites that enhances the risk to rainstorms. Spider mites live on the undersides of host plant leaves and usually oviposit on the leaf undersurface. When they are threatened by predatory mites, they oviposit on three-dimensional webs to avoid egg predation, although the cost of ovipositing on webs has not yet been clearly determined. We prepared bean plants harbouring spider mite (Tetranychus kanzawai) eggs on either leaf surfaces or webs and exposed them to rainstorms outdoors. We found that fewer eggs remained on webs than on leaf surfaces. We then examined the synergistic effect of wind and rain by simulating both in the laboratory. We conclude that ovipositing on webs comes at a cost, as eggs are washed off the host plants by wind and rain. This may explain why spider mite populations decrease drastically in the rainy season, although they inhibit leaf undersides where they are not directly exposed to rainfall.

Age-Dependent Functional and Numerical Responses of Neoseiulus cucumeris (Acari: Phytoseiidae) on Two-Spotted Spider Mite (Acari: Tetranychidae).

The age-specific functional and numerical responses of Neoseiulus cucumeris Oudemans (Mesostigmata: Phytoseiidae) on eggs of the two-spotted spider mite, Tetranychus urticae Koch (Prostigmata: Tetranychidae), were assessed in the laboratory using bean leaf discs. Densities of 2, 4, 8, 16, 32, 64, and 128 prey were provided to 4- (protonymph), 6- (deutonymph), 8-, 13-, 18-, 23-, 28-, 33-, and 40-d-old N. cucumeris individuals. The functional response of 28- and 40-d-old N. cucumeris fitted type II, whereas the other ages displayed a type III functional response. The longest handling time observed at the age of 4 d was 0.515 h, whereas the shortest handling time and highest value of maximum attack rate (T/Th) were associated with the age of the 28-d-old treatment (0.261 h and 91.95 prey/d, respectively). The numerical response of N. cucumeris showed a significant increase with increasing prey density, but its rate gradually decreased at higher densities. Therefore, the efficiency of conversion of ingested food was relatively higher at low two-spotted spider mite densities, whereas it was reduced at high two-spotted spider mite densities. The stronger functional response and predation capacity of N. cucumeris on two-spotted spider mite eggs indicated the high potential of this predatory mite as an effective biological control agent against two-spotted spider mite especially at its early and middle ages and also when higher prey densities are present.

BIOLOGICAL ACTIVITIES OF ESSENTIAL OILS FROM ANETHUM GRAVEOLENS L. AND ALLIUM SATIVUM L. FOR CONTROLLING TETRANYCHUS TRUNCATUS EHARA AND TETRANYCHUS URTICAE KOCH

ABSTRACT The essential oils of Anethum graveolens L. and Allium sativum L. were investigated for the biological activities against Tetranychus urticae Koch and Tetranychus truncatus Ehara. The results indicated that A. sativum oil at 20% (v/v) had high contact toxicity (73.50% mortality) on adult females of T. truncatus. The LC50 value was 12.71% for 24 h after treatment. Eggs of both spider mites were also susceptible to 5-20% and 20% concentrations of A. sativum and A. graveolens oil, respectively. Allium sativum oil caused 97-100 and 84% mortality against T. truncatus and T. urticae eggs with LC50 values of 1.62 and 11.58% at 7 d after exposure, respectively. In repellency test, A. graveolens oil at 5-20% concentrations showed a high percentage of repellency on T. truncatus (62-96%) and T. urticae (98-100%) during 1-5 h after treatment. On the other hand, 5-20% and 15-20% concentrations of A. sativum oil appeared high percentage of repellency on T. truncatus (98-100%) and T. urticae (86-100%) during 1-5 h after treatment, respectively. In a fumigant toxicity test, A. sativum and A. graveolens oils were toxic to both spider mites. Allium sativum oil (LC50 = 4.94 µL/L in air) and A. graveolens oil (LC50 = 13.67 µL/L in air) were toxic to adult females of T. urticae whereas T. truncatus adult females were responsible to A. graveolens oil (LC50 = 5.24 µL/L in air) and A. sativum oil (LC50 = 5 µL/L in air). The results suggested that essential oils of A. sativum had potential for ovicidal activity on T. truncatus and T. urticae and acaricidal activity on T. truncatus. Both oils showed repellent activity against both spider mites. Oils of A. sativum and A. graveolens were toxic in fumigant effect on both spider mites. Their biological activities could be useful in promoting of integrated mite management.

Twospotted Spider Mites (Tetranychus urticae) on Strawberry (Fragaria × ananassa) Transplants, and the Potential to Eliminate Them with Steam Treatment

ABSTRACT The twospotted spider mite (Tetranychus urticae) is a serious pest of strawberries. The objectives of this study were to determine incidence and severity of twospotted spider mite infestations on transplants and the potential for steam to eliminate them. Mites occurred on transplants of Florida cultivars from each of eight North American nurseries from which samples were obtained, but levels were usually low (59% of samples had zero mites). Estimated complete mortality of twospotted spider mite adult females and eggs on leaf discs using steam at 48°C was 2.7 and 1.9 h, respectively; 44°C and 46°C for up to 4 h killed 20% and 60% of the mites, respectively. Based on these results, eliminating twospotted spider mites on transplants is feasible and may be valuable for improving their management in fruit-production fields.

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.

Influence of a Neonicotinoid Seed Treatment on a Nontarget Herbivore of Soybean (Twospotted Spider Mite) and Diet Switching by a Co-occurring Omnivore (Western Flower Thrips).

Insecticidal neonicotinoid seed treatments are a common agricultural insect pest management strategy; however, effects on nontarget pests and omnivorous arthropods are understudied. We used a series of experiments to evaluate impacts of the neonicotinoid seed treatment thiamethoxam on densities of herbivorous twospotted spider mites (Tetranychus urticae Koch [Acari: Tetranychidae]) and feeding behavior of western flower thrips (Frankliniella occidentalis Pergande [Thysanoptera: Thripidae]), an omnivore that feeds on spider mite eggs but is also a significant plant pest. Spider mite densities were higher on neonicotinoid-treated soybeans, but only when mites were not spatially confined. We then examined how availability of thiamethoxam-treated food items (i.e., eggs from spider mites reared on treated soybeans, soybean leaf discs, or a combination of the two), and previous exposure to thiamethoxam-treated soybean impacted thrips feeding. Regardless of the presence of leaf tissue, thrips consumed fewer spider mite eggs laid by females reared on treated soybeans, suggesting spider mite eggs can serve as poisoned prey. Overall, thrips consumed less treated soybean leaf tissue, and thrips on treated leaf discs had a lower percentage of herbivorous feeding events and consumed more nontreated spider mite eggs, indicating a dietary shift from herbivory to predation. The neonicotinoid status of spider mite eggs and prior exposure of thrips also caused shifts in the number and size of leaf scars, likely as a result of altered foraging behavior and/or movement. Shifts between herbivory and predation have implications for thrips damage, virus transmission, and pest management, especially in systems with mixtures of nontreated and neonicotinoid-treated plants.

Design, Synthesis, Acaricidal Activities, and Structure-Activity Relationship Studies of Novel Oxazolines Containing Sulfonate Moieties.

With the ultimate goal of addressing pest-related constraints on global agricultural production, we used combination principles to design and synthesize 2,4-diphenyl-1,3-oxazolines containing a sulfonate moiety at the para-position of the 4-phenyl group. The target compounds, which have strong affinity for lipids and can be expected to traverse cell membranes, were characterized by 1H and 13C NMR spectroscopy and high-resolution mass spectrometry. Their activities against the larvae and eggs of carmine spider mites (Tetranychus cinnabarinus) were determined by a leaf-dipping method and compared with the activity of the commercial acaricide etoxazole. Most of the test compounds displayed good ovicidal and larvicidal activities. In particular, a tert-butylphenyl-substituent compound possessed better larvicidal activity (LC50 = 0.022 ± 0.009 mg/L) and ovicidal activity (0.044 ± 0.020 mg/L) than etoxazole (0.091 ± 0.051 and 0.095 ± 0.059 mg/L, respectively). Given its outstanding bioactivities, this compound deserves further attention as a pesticide candidate.

Synthesis and Acaricidal- and Insecticidal-Activity Evaluation of Novel Oxazolines Containing Sulfiliminyl Moieties and Their Derivatives.

Sulfimides and sulfoximines are highly relevant for medicinal chemistry and crop protection, as the resulting products can reveal interesting bioactivities. Herein, we report the design and synthesis of a series of novel 2,4-diphenyl-1,3-oxazolines containing sulfiliminyl and sulfoximinyl moieties. The acaricidal and insecticidal activities of the new compounds were evaluated and indicated that these compounds exhibited excellent acaricidal activities against spider mite larvae and eggs. The LC50 values of 6a-7, 6b-3, 6b-4, 6c-2, and 6c-4 against spider mite larvae were about 4 to 6 times lower than that of the commercial insecticide etoxazole (0.0221 mg L-1), and the LC50 value of 6a-4 against spider mite eggs was 0.0006 mg L-1, which was 10 times lower than that of etoxazole (0.0063 mg L-1). At the same time, most of the compounds showed insecticidal activity though their structure-activity relationships that were different. Oxazolines containing an N-cyano sulfiliminyl moiety at the para position of the 4-phenyl group exhibited better insecticidal activities against cotton bollworm and corn borer than etoxazole, whereas the compounds containing groups derived from sulfiliminyl and sulfoximinyl had weak insecticidal activities. This research again proved that the substituent type at the para site of the 4-phenyl moiety has a decisive role on the biological activity and insecticidal spectrum.

Food decisions of an omnivorous thrips are independent from the indirect effects of jasmonate-inducible plant defences on prey quality

Plant defensive substances can affect the quality of herbivores as prey for predators either directly or indirectly. Directly when the prey has become toxic since it ingested toxic plant material and indirectly when these defences have affected the size and/or nutritional value (both quality parameters) of prey or their abundance. To disentangle direct and indirect effects of JA-defences on prey quality for predators, we used larvae of the omnivorous thrips Frankliniella occidentalis because these are not directly affected by the jasmonate-(JA)-regulated defences of tomato. We offered these thrips larvae the eggs of spider mites (Tetranychus urticae or T. evansi) that had been feeding from either normal tomato plants, JA-impaired plants, or plants treated with JA to artificially boost defences and assessed their performance. Thrips development and survival was reduced on the diet of T. evansi eggs relative to the diet of T. urticae eggs yet these effects were independent from the absence/presence of JA-defences. This indicates that the detrimental effects of tomato JA-defences on herbivores not necessarily also affects their quality as prey.

Mint companion plants attract the predatory mite Phytoseiulus persimilis

Mint plants could theoretically serve as companion plants (CPs) that attract enemies of herbivores in tritrophic interactions. In order to explore the traits of mint volatiles as attractant cues for enemies of two-spotted spider mites, we performed Y-tube olfactometer assays of predatory mites, Phytoseiulus persimilis and Neoseiulus californicus, towards three mint species, apple mint, candy mint, and spearmint, as odor source. Clean candy mint and spearmint were attractive to P. persimilis, when compared with clean air and undamaged Phaseolus vulgaris plants serving as the target crop. Moreover, clean candy mint plants were even more attractive than volatiles from P. vulgaris plants damaged by spider mites. These predator responses were induced additively by candy mint volatiles plus volatiles from damaged P. vulgaris plants, as shown using both Y-tube olfactometer and open-space assay systems. However, the number of spider mite eggs consumed by P. persimilis on P. vulgaris plants did not differ in the presence compared to the absence of mint volatiles, indicating that mint volatiles affect the attraction but not the appetite of P. persimilis. Together, these findings suggest that the use of candy mint and spearmint as CPs is an ideal platform for spider mite pest management via the attraction of predatory mites.

THE SURFACE OF THE LEAF BLADE AS A FACTOR INFLUENCING THE SPIDER MITES DEVELOPMENT ON CUCUMBER

A comparative assessment of spider mite eggs development on the upper and under side of cucumber cotyledons has been made under laboratory experiments on the varieties Ginga F1 and Vyaznikovsky 37. Studies have been conducted on the cotyledons cut off from growing plants and placed on a wet cotton wool in the Petri dish. Mite eggs laid by females for five hours have been used for work. It has been shown that mites develop more slowly on the underside of cotyledons in comparison to the upper side when cotyledons are not exposed to spider mite. This may be due to the peculiarities of gas exchange on the abaxial and adaxial sides of leaves. It has been also found, that the mite embryonic development duration is increased, if occurs on the underside of the cotyledon , damaged by the spider mite within 1 day. Apparently, this is caused by the plant defense reactions to herbivory occurring increasingly on the lower side of cotyledons and associated with volatiles that has adverse effect on the mite eggs development. It is assumed that responses to the spider mites damage in the cucumber cotyledon leaves (in particular, those associated with the releasing of volatile compounds) are more characteristic for the spongy parenchyma cells than for the palisade cells in the leaf mesophyll.

Effects of cultivar and leaf traits on the abundance of Pacific spider mites in almond orchards

A greater understanding of the ecological relationships between Pacific spider mite, Tetranychus pacificus, and its almond host is needed for better management recommendations and reduced need for pesticides. Since populations of T. pacificus are thought to increase with deficit irrigation and fertilization, they may also differ between almond cultivars varying in leaf traits relating to water use and leaf nitrogen (N) content. In the current study, the relationships between T. pacificus populations, almond cultivars and leaf traits were examined at studies in two locations. In the first study, a large-scale cultivar trial with a high level of T. pacificus infestation, spider mite eggs were more common on the cultivar ‘Sweetheart’ than either ‘Nonpareil’ or ‘Marcona,’ and across all cultivars, mites and leaf damage increased with stomatal density, but decreased with stomatal length. Almond cultivars differed in traits, with ‘Sweetheart’ having the highest leaf N and ‘Marcona’ the lowest stomatal density. In the second study, a germplasm repository orchard collection with low levels of T. pacificus infestation, spider mites were not detected on the cultivar ‘Mission’ but were similarly highest on ‘Sweetheart.’ Mites increased with N across all cultivars, and leaf damage due to spider mites increased with more negative δ13C, indicating low water use efficiency. Results suggest that monitoring of spider mite populations should include conditions of high nutrient and water availability, especially for susceptible cultivars, and that spider mite populations are not consistently higher with leaf traits indicating water stress.