Compositional Optimization for Miticidal Activity, Ecotoxicity, and Phytotoxicity of Rosmarinus officinalis Essential Oils as Biorational Pesticides.

Recognizing the challenges in using botanicals as sustainable pest control agents due to compositional variation, this study addresses the limitations of traditional component-based approaches such as Hewlett and Plackett or Wadley's models. Based on the assumption of noninteractivity among constituents, these models often fail to predict outcomes accurately due to dynamic intermolecular interactions. We introduce a whole mixture-based approach, employing a combination of experimental design and polynomial modeling. This technique accurately predicts miticidal activity on Tetranychus urticae, ecotoxicity on Daphnia magna, and phytotoxic activities on Phaseolus vulgaris of Rosemarinus officinalis essential oils with varying composition. The RMSE values from the polynomial model are 66.9 and 5.0 for miticidal activity and ecotoxicity, respectively, while they are much higher in component-based models, up to 1097.7 and 41.3, respectively. Additionally, we utilize multiobjective optimization algorithms to identify the optimal supplementary blending of oils and compounds. This strategy aims to maximize miticidal effectiveness while minimizing ecotoxicity and phytotoxicity. Our approach for predicting multicomponent mixture effects is likely to bridge the knowledge gap between research and commercialization.

Unveiling FM-1088: A Breakthrough in Isoindolinone-Based Acaricide Development.

The increasing resistance of agricultural pests to existing acaricides presents a significant challenge to sustainable agriculture. Therefore, this study introduced FM-1088, a novel isoindolinone-based phenyl trifluoroethyl thioether derivative generated through an innovative design strategy combining bioisosterism and novel cyclization methods. We synthesized several compounds and evaluated their acaricidal efficacy against Tetranychus cinnabarinus in greenhouses and Panonychus citri in field settings. FM-1088 emerged as a standout candidate, demonstrating a lower median lethal concentration (LC50) of 0.722 mg/L compared to the commercial acaricide, cyetpyrafen. Notably, 30 days after application, FM-1088 showed a field control efficacy of 96.4% against P. citri, highlighting its potential for broader applications. The results underscore the utility of the isoindolinone scaffold in pesticide development, offering a promising solution to combat pest resistance with implications for enhanced crop protection and agricultural productivity. Future studies should explore the detailed mode of action of FM-1088 and its potential applicability across diverse agricultural settings, further confirming its role as a sustainable solution for pest management.

Evaluation of the temperature adaptation of three rubber tree pest mites based on their two-sex life table.

To determine the optimal temperature range for the development and reproduction of three spider mites (Eotetranychus sexmaculatus, Eotetranychus orientalis, and Oligonychus biharensis), this study investigated their developmental period, survival rate, lifespan, and reproduction under five temperatures, 21, 24, 27, 30, and 33°C, to predict and control in the field. With the gathered data, a two-sex life table was constructed for each of them. The results revealed that as the temperature increased, both O. biharensis and E. orientalis displayed a gradual reduction in their generation period. Furthermore, an inverse relationship was observed between lifespan and temperature for all three spider mite species. When examining the survival rates at varying temperatures, E. sexmaculatus exhibited the highest rate (98%) at 33°C, while E. orientalis and O. biharensis demonstrated their highest survival rates at 24°C, reaching 90% and 100% respectively. Regarding reproduction, O. biharensis displayed the highest oviposition rates at 30°C with an average of 17.45 eggs per individual. Conversely, E. sexmaculatus and E. orientalis exhibited the highest oviposition rates at 33°C, averaging at 15.22 and 21.38 eggs per individual respectively. Significantly higher intrinsic growth rates were observed for O. biharensis and E. orientalis at 33°C, with rates of 0.22 and 0.26 respectively. In contrast, E. sexmaculatus demonstrated the highest intrinsic growth rate at 27°C. The temperature of 27°C was more suitable for the growth of the E. sexmaculatus, while 33°C was the optimal temperature for the E. orientalis and O. biharensis. The current findings provide valuable guidance for the control and prevention of these three spider mites.

Effect of Eucalyptus globulus and Ferula assafoetida essential oils and their nanoformulations on the life table parameters of Tetranychus urticae (Acari: Tetranychidae).

One of the most damaging pests of agricultural crops across the globe is the two-spotted spider mite, Tetranychus urticae Koch. A wide variety of arthropods and plant pathogens can be controlled by essential oils, which are secondary metabolites produced by plants. It is possible to enhance the stability as well as the anti-pest efficiency of plant essential oils by encapsulation. Water distillation was used to extract the essential oils from Eucalyptus globulus and Ferula assafoetida. The chitosan nanoparticles were used to load both essential oils into nanoformulations. Studies were conducted on T. urticae life table characteristics under experimental circumstances to determine the sublethal impacts of essential oils and their nanoformulations. Intrinsic growth rate (r) for population exposed to E. globulus, F. assafoetida essential oils, their nanoformulations and the control were 0.1, 0.069, 0.051, 0.018 and 0.21 per day, respectively. F. assafoetida and E. globulus nanoformulations resulted the lowest fecundity compared to the other treatments. According the result of the lethal and sublethal effects of purified essential oils and nanoformulations of F. assafoetida and E. globulus, they would be recommended for controlling the two-spotted spider mites, T. urticae.

The chitinase genes TuCht4 and TuCht10 are indispensable for molting and survival of Tetranychus urticae.

Insect chitinases (Chts) play a crucial role in the molting process, enabling continuous growth through sequential developmental stages. Based on their high homology to insect Chts, TuCht1 (group II), TuCht4 (group I) and TuCht10 (group IV) were identified, and their roles during molting process were investigated. TuCht1 was mainly expressed in the deutonymphal stage, while TuCht4 was mainly expressed in the nymphal stage and the highest expression level of TuCht10 was observed in the larvae. Feeding RNAi assays have shown that group I TuCht4 and group Ⅳ TuCht10 are involved in mite molting. Suppression of TuCht4 or TuCht10 resulted in high mortality, molting abnormalities and the absence of distinct electron dense layers of chitinous horizontal laminae in the cuticle, as demonstrated by scanning electron microscopy and transmission electron microscopy. The nanocarrier mediated RNAi had significantly higher RNAi efficiency and caused higher mortality. The results of the present study suggest that chitinase genes TuCht4 and TuCht10 are potential targets for dietary RNAi, and demonstrates a nanocarrier-mediated delivery system to enhance the bioactivity of dsRNA, providing a potential technology for green pest management.

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.

Molecular insight into the endophytic growth of Beauveria bassiana within Phaseolus vulgaris in the presence or absence of Tetranychus urticae.

Entomopathogenic fungi are an important factor in the natural regulation of arthropod populations. Moreover, some can exist as an endophyte in many plant species and establish a mutualistic relationship. In this study, we have investigated the endophytic growth of Beauveria bassiana within different tissues of Phaseolus vulgaris in the presence and absence of Tetranuychus urticae. After the colonization of the B. bassiana within the internal tissues of P. vulgaris. The susceptibility of T. urticae appeared to depend on the life stage where high, moderate, and low mortalities were recorded among adults, nymphs, and eggs, respectively. In addition, this study provided, for the first time, molecular insight into the endophytic growth of B. bassiana by analyzing the expression of several genes involved in the development of the entomopathogenic fungi at 0-, 2-, and 7- days post-inoculation. B. bassiana displayed preferential tissue colonization within P. vulgaris that can be put into the following order based on the detection rate: leaf > stem > root. After analyzing the development-implicated genes (degrading enzymes, sugar transporter, hydrophobins, cell wall synthesis, secondary metabolites, stress management), the most remarkable finding is the detection of behavioral change between parasitic and endophytic Beauveria during post-penetration events. This study elucidates the tri-trophic interaction between fungus-plant-herbivore.

Transcriptome of Tetranychus urticae embryos reveals insights into Wolbachia-induced cytoplasmic incompatibility.

The endosymbiont Wolbachia is known for manipulating host reproduction in selfish ways. However, the molecular mechanisms have not yet been investigated in embryos. Here, we found that Wolbachia had no effect on the number of deposited eggs in Tetranychus urticae Koch (Acari: Tetranychidae) but caused two types of reproductive manipulation: killing uninfected female embryos via cytoplasmic incompatibility (CI) and increasing the hatching ratio of infected female embryos. RNA sequencing analyses showed that 145 genes were differentially expressed between Wolbachia-infected (WI) and Wolbachia-uninfected (WU) embryos. Wolbachia infection down-regulated messenger RNA (mRNA) expression of glutathione S-transferase that could buffer oxidative stress. In addition, 1613 and 294 genes were identified as CI-specific up-/down-regulated genes. Compared to WU and WI embryos, embryos of CI cross strongly expressed genes involved in transcription, translation, tissue morphogenesis, DNA damage and mRNA surveillance. In contrast, most of the genes associated with energy production and metabolism were down-regulated in the CI embryos compared to the WU and WI embryos, which provides some clues as to the cause of death of CI embryos. These results identify several genes that could be candidates for explaining Wolbachia-induced CI. Our data form a basis to help elucidate the molecular consequences of CI in embryos.

Preparation of Matrinic/Oxymatrinic Amide Derivatives as Insecticidal/Acaricidal Agents and Study on the Mechanisms of Action against Tetranychus cinnabarinus.

In continuation of our program to develop natural-product-based pesticidal candidates, matrinic/oxymatrinic amides were obtained through structural optimization of matrine. N'-(4-Fluoro)phenyl-N-(4-bromo)phenylsulfonyloxymatrinic amide (IIm) showed potent insecticidal activity against Mythimna separata. N-(Un)substituted phenylsulfonylmatrinic acids (3a-c) exhibited promising acaricidal activity against Tetranychus cinnabarinus. By qRT-PCR analysis of nAChR subunits and AChE genes and determination of AChE activity of (un)treated T. cinnabarinus, it suggested that the open lactam ring of matrine and carboxyl group and (4-methyl)phenylsulfonyl of N-(4-methyl)phenylsulfonylmatrinic acid (3b) were necessary for action with α2, α4, α5, and ß3 nAChR subunits; compound 3b was an inhibitor of AChE in T. cinnabarinus, and AChE was one possible target of action in T. cinnabarinus against 3b; and compound 3b may be an antagonist of nAChR and AChE in T. cinnabarinus.

Development, lifespan and reproduction of spider mites exposed to predator-induced stress across generations.

Predator-induced stress shows pronounced effects on prey by inducing behavioural, morphological, and physiological responses. Increasing evidence shows that these antipredator responses may also lead to changes in life-history traits such as aging and lifespan. However, little is known about how predator cues influence the fitness of preys and their transgenerational effects. Parental spider mites (Tetranychus urticae) were either raised on a leaf disc with or without cues from a natural predator (Phytoseiulus persimilis). The results showed that predator cues prolonged the development of both sexes, shortened female adult lifespan but not that of males, and reduced lifetime reproductive outputs of the females. The studies with offspring from both cues-exposed and control mothers demonstrated that parental effects were significant in the early developmental stage of offspring, but not in later life stages. The lifespan of offspring was strongly negatively affected by the predator-induced stress when they were directly exposed but not the stress-experienced by their mothers. Additionally, the parental effects in the earlier life stage were sex-specific, with delayed hatching in daughters (but not sons) when parents were exposed to predator-induced stress. This cross-transgenerational study indicated that there were deleterious effects of predator-induced stress on aging and lifespan of prey for both parents and their offspring, although the parental effects appeared to be weak (in the early stage of offspring but diminished in adult stage). This study highlighted the sex-difference of prey in response to predator-induced stress and sex-dependent parental effects on the offspring.

Seasonal occurrence and development of three closely related Oligonychus species (Acari: Tetranychidae) and their associated natural enemies on fagaceous trees.

We compared the life cycles and diapause attributes among three closely related spider mites, Oligonychus castaneae on Castanea crenata, and O. gotohi and O. amiensis on Lithocarpus edulis. The lower thermal thresholds from egg to egg were 10.5, 8.5 and 8.9 °C, respectively, and the thermal constants were 177.8, 229.5 and 232.5 degree-days, respectively. The cumulative hatching rates of diapause eggs of O. castaneae and O. gotohi increased as the season progressed in and after early-to-mid January, which indicates diapause termination. In contrast, O. amiensis showed higher hatching rates in December and January, but hatchability gradually decreased in and after February because some of the eggs died from the cold. Oligonychus castaneae and O. gotohi females produced diapause eggs in response to the short photoperiod in late September to early October and in early-to-late October, respectively, which corresponded to the times predicted by the critical photoperiods (at 15 °C) of 12 h 15 min and 11 h 15 min for the respective species. Oligonychus castaneae showed at least a single population peak over the 3-year observation period, but the time of peak population varied from mid-July to mid-September. The population of O. gotohi was higher between November and May when diapause eggs were present on host plants in early winter and the first-generation females laid eggs on leaves in spring. The population of O. amiensis, which is a non-diapause species, was only high between September and December, because eggs were laid on leaves in autumn to winter and then gradually disappeared and/or died during winter. Natural enemies were observed as the number of spider mites declined, and the density suppression effect by natural enemies was confirmed in the field.

RNAi targeting ecdysone receptor blocks the larva to adult development of Tetranychus cinnabarinus.

RNA interference (RNAi) is a potentially useful pest control method because of its high specificity. Silencing the expression of important RNAi target genes of pests will block important biological processes and reduce pest damage. Ecdysone is a unique arthropod hormone and the ecdysone receptor (EcR) is a key factor in molting pathway. We investigated the possibility that dsRNA targeting of the EcR of Tetranychus cinnabarinus (TcEcR) could effectively block development from larvae to adults. The mRNA level of TcEcR was highest in the larva stage, and 73.1% of the mites failed to survive the larva stage when TcEcR expression was silenced. Only 11.7% of T. cinnabarinus ingesting dsRNA successfully developed into adults, while 86.7% in the control succeeded in molting across each stage. RNAi significantly increased the developmental intervals of T. cinnabarinus. Under the effects of dsRNA, development times for the larva and first nymph doubled. Phenotype of body size change and death were observed during the development of T. cinnabarinus ingesting dsRNA. These findings suggest that RNAi is a potential means for the control of T. cinnabarinus. Genes in hormone pathways such as EcR are possible RNAi targets.

Production of winter eggs in Schizotetranychus brevisetosus (Acari: Tetranychidae) inhabiting evergreen Japanese blue oak.

The overwintering pattern of parasitic herbivorous arthropods is closely related to host phenology, because defoliation imposes strong selection pressures on various developmental stages. This relationship has been well studied in populations of spider mites (Acari: Tetranychidae) on deciduous hosts, but is little studied in populations on evergreen hosts, probably because their leaves are always available. However, spring defoliation may also influence the life cycle. We studied the overwintering pattern of Schizotetranychus brevisetosus (Acari: Tetranychidae), a specialist on evergreen oak, Quercus glauca, in Kochi, Japan. Only adult females and their eggs (winter eggs) survived the coldest months. We also observed a conspicuous seasonal change in egg colour and size: December winter eggs were 1.7× larger than September summer eggs, suggesting the winter eggs are diapausing. Adult females produced summer eggs until November and winter eggs from late November until they disappeared in March. The winter eggs hatched in early March. The immature stages developed in mid- to late March, when 39% of old leaves fell, some of which carried hundreds of immature individuals. Therefore, even in evergreen hosts, defoliation places potentially strong selection pressure on the immature stages. Despite this, S. brevisetosus appears not to change its egg hatching season to avoid the defoliation season, so it may have evolved a behavioural adaptation to escape falling leaves. The existence of several species with similar lifestyles suggests the importance of host phenology and predation pressure for evolution of the overwintering pattern.

Peanut cultivars display susceptibility by triggering outbreaks of Tetranychus ogmophallos (Acari: Tetranychidae).

The peanut red spider mite, Tetranychus ogmophallos Ferreira and Flechtmann (Acari: Tetranychidae), is an important pest of peanut in Brazil and is considered a quarantine pest in other countries. This study investigates the development, reproduction, survival and life table parameters of T. ogmophallos on five peanut cultivars-three with high levels of oleic acid [high oleic] and recently released: Granoleico, IAC OL 3 and IAC 503; and two regular and previously used by farmers: Runner IAC 886, IAC Tatu ST 3-and two breeding lines (L. 8008 and L. 322) in the growth chamber. There were differences between the developmental times of all immature stages, the oviposition period, fecundity and adult longevity of T. ogmophallos reared on the peanut cultivars and breeding lines. The longest duration of the immature stage and lowest fecundity occurred on cultivars Granoleico and Runner IAC 886, and breeding line L. 322, which also displayed the lowest intrinsic rate of increase (r), finite rate of increase (λ) and net reproductive rate (R0) and the shortest mean generation time (T). The highest fitness occurred on the IAC Tatu ST, IAC OL 3, IAC 503 and L. 8008. Our study shows that peanut cultivars belonging to the group with high oleic trait and recently released (IAC OL 3 and IAC 503) are susceptible to T. ogmophallos, except Granoleico, which is resistant. The regular and previously used cultivar Runner IAC 886 and breeding line L. 322 are resistant to the peanut red spider mite.

Expression dynamics of key ecdysteroid and juvenile hormone biosynthesis genes imply a coordinated regulation pattern in the molting process of a spider mite, Tetranychus urticae.

In insects, the ecdysteroid 20-hydroxyecdysone coordinates with juvenile hormone (JH) to regulate the process of molting, development and metamorphosis; however, this interaction is still unclear in the mites. In this study, we investigated the gene related to ecdysteroid and JH biosynthesis pathways, including four ecdysteroid and 11 JH biosynthesis genes. We examined their expression patterns during molting of different developmental stages of the two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), an important agricultural pest that feeds on more than 1100 plant species. The expression of ecdysteroid biosynthesis Halloween genes exhibited a positive zigzag-like pattern, with a peak after 8 h of molting and a drop 8 h after entering each quiescent stage. In contrast, JH biosynthesis genes expression displayed a negative zigzag-like pattern, with a peak at 8 h after entering each quiescent stage and a drop after 8 h of each molting. These opposite patterns imply that ecdysteroid and JH expression is coordinated during the developmental transition. Our data provide an initial perspective on the co-expression of ecdysteroid and JH biosynthesis genes to regulate this important developmental process in the two-spotted spider mite.

Population performance of Tetranychus evansi (Acari: Tetranychidae) on African tomato varieties and wild tomato genotypes.

The tomato red spider mite, Tetranychus evansi Baker & Pritchard, is one of the main pests of the tomato crop in several countries, mainly in Africa, where it can reduce tomato yield by up to 90%. The biotic potential of this mite is high and its control is difficult because of low efficiency of chemicals used and the rapid development of resistance to acaricides. We used the two-sex life table to evaluate the effect of two wild tomato genotypes (PI134417 and PI134418) and five tomato varieties widely grown in Benin (Kekefo, Akikon, TLCV15, Tounvi, and TOML4) on demographic characteristics of T. evansi under laboratory conditions. Tetranychus evansi did not develop on the genotypes PI134417 and PI134418, indicating their resistance to this mite. Developmental time of immature stages and female longevity were significantly higher on TLCV15 and Kekefo. Fecundity, net reproductive rate (R0), intrinsic rate of increase (r), and finite rate of increase (λ) of T. evansi on the African varieties were not statistically different among varieties. Generation time (T) was shorter on TOML4 than on TLCV15 and Tounvi. Thus, efforts should be made to prospect varieties with resistance characteristics or to develop other control means, to reduce the use of pesticides to control T. evansi in Africa.

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.

Spraying pyrethroid and neonicotinoid insecticides can induce outbreaks of Panonychus citri (Trombidiformes: Tetranychidae) in citrus groves.

Panonychus citri (McGregor) (Trombidiformes: Tetranychidae) is one of the main defoliator mites in citrus groves. In Brazil, P. citri was formerly considered a secondary pest, but in recent years, the population levels of this mite have increased in many groves, requiring additional acaricide applications for its control. The population growth of P. citri is associated with the increase in the number of applications of pyrethroid and neonicotinoid insecticides to control insect citrus pests. This study assessed the effects of pyrethroid (deltamethrin, esfenvalerate, λ-cyhalothrin) and neonicotinoid (imidacloprid and thiamethoxam) insecticides on biological, behavioral and demographic parameters of P. citri. None of the insecticides tested affected larval hatching, but deltamethrin, esfenvalerate, and λ-cyhalothrin reduced the survival of larvae and protonymphs. Deltamethrin, esfenvalerate, and λ-cyhalothrin induced a significant increase in the fecundity of surviving females. Pyrethroids also caused repellency and changed feeding and oviposition preferences. In contrast, imidacloprid and thiamethoxam did not affect the survival of immature stages, but imidacloprid significantly increased fecundity. Imidacloprid and thiamethoxam did not cause any repellent effect or changes in the feeding and oviposition preferences. Based on the demographic parameters, deltamethrin, λ-cyhalothrin, and imidacloprid increased Ro, r, and λ, whereas esfenvalerate and thiamethoxam were similar to the control. Therefore, the use of these insecticides (especially deltamethrin, λ-cyhalothrin, and imidacloprid) requires caution, such as avoiding repeated use of these compounds during the periods of P. citri incidence in citrus groves.

Acaricidal Activity of Cyclodipeptides from Bacillus amyloliquefaciens W1 against Tetranychus urticae.

Bioassay-guided fractionation of the supernatant of the biocontrol strain Bacillus amyloliquefaciens W1 led to the isolation of eight acaricidal cyclodipeptides from the active fractions by column chromatography separation and HPLC purification. The chemical structures of these compounds were identified as cyclo-(Gly-l-Phe), 2, cyclo-(l-Phe- trans-4-OH-l-Pro), 3, cyclo-(Gly-l-Tyr), 4, cyclo-(l-Ala-l-Pro), 5, cyclo-(l-Pro- trans-4-OH-l-Pro), 6, cyclo-(Gly-l-Pro), 7, cyclo-(l-Pro-l-Pro), 8, and cyclo-(l-Tyr- trans-4-OH-l-Pro), 9. Those cyclodipeptides displayed significant acaricidal activities with LC50 values of 13.85-98.24 µM. Cyclo-(l-Tyr- trans-4-OH-l-Pro) (LC50 13.85 µM) was five times more effective than the positive control abamectin (LC50 72.06 µM). The results indicated that the hydroxyl group is an important component. This is the first report on the acaricidal capabilities of cyclodipeptides against Tetranychus urticae. The results revealed that the acaricidal activity of the biocontrol strain B. amyloliquefaciens W1 was dependent on its constituent cyclodipeptides, which have the potential to be safe and environmentally friendly acaricides.

Preference and performance of the two-spotted spider mite Tetranychus urticae (Acari: Tetranychidae) on strawberry cultivars.

The two-spotted spider mite (TSSM), Tetranychus urticae Koch (Acari: Tetranychidae), is one of the most serious pests of strawberry worldwide. Understanding the preference of TSSM for particular cultivars of strawberry and performance on them helps identify host-plant resistance to this pest mite. In this study, we tested preference, developmental duration, fecundity and population levels of TSSM on 14 strawberry cultivars. TSSM showed strong preference for the Chinese cultivars of Yanxiang, Baixuegongzhu, and Jingtaoxiang. Development of TSSM on the cultivars varied from 32.32 to 36.82 days; it was longest on the cultivars Hongxiutianxiang and Baixuegongzhu, and shortest on Yanxiang, Jingzangxiang, and Darselect as well as on a wild variety (Wuye). TSSM had high fecundity on the cultivars Yanxiang, Taoxun, Hongxiutianxiang, Jingzangxiang, Albion and Baixuegongzhu as well as on Wuye, whereas egg production was lowest on Sweet Charlie, Portola, Akihime, and Benihoppe. After 28 days of plant infestation with 10 pairs of adults, the cultivars Yanxiang, Taoxun, Jingzangxiang, Jingtaoxiang, and Baixuegongzhu had the highest number of mites (> 1000 per plant), whereas mite numbers on Albion and Camarosa were low. The population size of TSSM was correlated with fecundity, but no correlation was found between other preference/performance measures. Our study suggests that a rapid increase of population size of TSSM on cultivars of strawberry is related to high fecundity, and also that there are substantial differences in preference and performance across cultivars.