Effects of sublethal concentrations and application concentration of SYP-9625 on Tetranychus cinnabarinus (Boisduval) and its natural enemy, Neoseiulus californicus (McGregor)

Objective Exploring the effects of acaricides on predatory mites is crucial for the combination of biological and chemical control of pests. In this study, sublethal effects of the new acaricide SYP-9625 on Tetranychus cinnabarinus (Boisduval), effects of application concentration of SYP-9625 on the predatory mite Neoseiulus californicus (McGregor) and functional responses of N. californicus were assessed. The aim of the present study was to evaluate and explore the application of new acaricide SYP-9625 with natural enemy N. californicus. Method All the experiments were under laboratory conditions [25 ± 1 °C, 16:8 (L:D) h and 75 ± 5% RH] and based on an age-stage, two-sex life table. The sublethal concentrations against T. cinnabarinus, including LC10 (0.375 μg/mL) and LC30 (0.841 μg/mL) and the application concentration (100 μg/mL) of SYP-9625, were used to evaluate effects on population parameters of N. californicus. Result T. cinnabarinus females treated with LC30 exhibited significantly reduced net reproductive rates (R0=11.02) of offspring compared to females treated with LC10 (R0=14.96) and untreated females (>R0=32.74). However, the intrinsic rate of increase (rm) and finite rate of increase (λ) of N. californicus indicated that the application concentration of SYP-9625 had no significant negative effect on treated N. californicus eggs (rm=0.277, λ=1.319) compared to the control (rm=0.292, λ=1.338). Additionally, the sublethal concentrations against T. cinnabarinus including LC10 and LC30 showed a dose-dependent mechanism on the predatory mite. SYP-9625 also stimulated the predatory capacity of N. californicus against immobile stages such as eggs and larvae. Conclusion It is demonstrated that sublethal concentrations of SYP-9625 can inhibit population growth of T. cinnabarinus. And the sublethal concentrations and application concentration had little effect on the population growth of N. californicus. The two advantages showed great commercial potential of this new acaricide. Therefore, N. californicus can manage T. cinnabarinus populations effectively with appropriate SYP-9625 concentrations.

Nowadays, agricultural spider mite pests are becoming serious threat to some important crops such as vegetables, fruits and ornamentals throughout the world. 48 Most spider mite pests, such as Tetranychus cinnabarinus (Boisduval), have rapid 49 development of resistance resulting from frequent applications of acaricides [1,2]. 50 Therefore, new acaricides which have excellent insecticidal activity and low toxicity 51 to natural enemies is increasingly needed [3]. 52 In the past few years, in order to combine natural enemies and acaricides, some 53 studies tend to paying more attention to the toxicity of acaricides toward predatory 54 mites. There might be inter-population differences in the sensitivities of these natural 55 enemies [4]. Lima evaluated different acaricide toxicity against Neoseiulus barkeri 56 (Hughes) and suggested that fenpyroximate and chlorfenapyr can be used with 57 predatory mite application [5]. Recently, sublethal effects of acaricides are more 58 considered than direct contact toxicity as an accurate approach to measure toxicity 59 [6]. Argolo found that the sublethal concentration of imidacloprid negatively affected 60 the population parameters of N. californicus, which provided a theoretical basis that 61 the compatibility of acaricides with natural enemies can be used to manage 62 agricultural pests [7]. Furthermore, the impact of insecticide on the functional 63 response of the predators was considered as a way to evaluate the effect of insecticide 64 on predation ability. The sublethal effects on powerful predation capacity of predatory 4 / 29 67 predation capacity of Phytoseiulus macropilis (Acari: Phytoseiidae) [4]. 68 The predatory mite, Neoseiulus californicus (McGregor) (Acari: Phytoseiidae group of substituents consisting of H, C 1 -C 4 alkoxy C 1 -C 2 alkyl, C 3 -C 5 alkenyloxy C 1 -113 C 2 alkyl, C 3 -C 5 alkynyloxy C 1 -C 2 alkyl, C 1 -C 4 alkylthio C 1 -C 2 alkyl, C 1 -C 5 alkyl 114 carbonyl, C 3 -C 8 cycloalkyl carbonyl, C 1 -C 5 alkoxy carbonyl or C 1 -C 5 alkylthio 115 carbonyl; R 2 is C l or methyl; R 3 is H, methyl, CN, NO 2 or halogen. Yu investigated 116 the syntheses and bioactivities of SYP-9625, and showed its excellent acaricidal 117 activity against T. cinnabarinus and low acute toxicity to mammals. pregnant N. californicus adults was placed in a petri dish that was supported by a 132 cotton pad filled with distilled water. After 12 h, mite females were placed on leaves to oviposit and then removed. The bean leaves with 50 eggs were dipped for 5 s in the 134 the solutions of SYP-9625 which were chosen based on initial rang-finding tests and 135 0.05% Tween 80 aqueous solution (control) and then placed upside down on a wet 136 cotton pad filled with distilled water. Eggs were checked every day and hatched in the 137 laboratory. There were four replicates per concentration.

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The two methods were also used for assessing the response of N. californicus 139 females and eggs to the application concentration of SYP-9625 (100 μg/mL) and even 140 ten times of it (100 μg/mL).   Where is the number of prey eaten, T is the experimental time (1h), is the Na 214 initial number of prey offered, is the searching (attack) rate, and is the handling a  lower than in the control. The curves moved backward and there was less 275 recombination (Fig 3). Moreover, the total survival rate at LC 30 was lower than the 276 LC 10 treatment and the control. In Fig 4,   The age-specific survival rate of females and age-stage specific survival rate of 310 treatment and control were observed (Fig 5). We can barely distinguish the difference 311 in l x , f x5 and m x in the total population between treatments and control. The peak value 312 of f x5 at control was 2 showed in 11 days and the peak value of f x5 at application 313 concentration was 1.8 showed in 10 days. r m , λ, GRR and T in treated N. californicus 314 eggs were similar with the control (Table 8)

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After assessed the effects of the application concentration on offspring from the 333 treated N. californicus females, the age-stage specific survival rate of egg and 334 protonymph ranged from 2 d to 3 d, and 3.5 d to 5 d after being treated (Fig 7). The 335 peak value of larva survival rate was above 0.8%, which was 0.3% higher than the 336 control. The survival rate of female adults was higher than males prior to the 337 application concentration application, but then the survival rate of female adults 338 decreased. The peak value was 0.4%, which was 0.2% lower than the control. value appeared to be delayed, and the declining gradient of the earlier stage was 347 higher than the control (Fig 8).  Table 9. Moreover, 354 there was no difference of T observed between treatments.  capacity of female adults against nymphs changed irregularly (Table 11).

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Table11 was uploaded as supported information in submission system.

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The functional response data of N. californicus fit reasonably well to a type-II  predatory capacities in the treatments were lower than the control.

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Table13 was uploaded as supported information in submission system.

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It was demonstrated that the functional response model was changed slightly Natural enemies were not only exposed to sublethal concentration of insecticides but 458 also fed on prey that exposed to sublethal concentration of insecticides. with two sublethal concentrations (LC 10 , LC 30 ) was longer than in the control.

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Furthermore, a/Th of treatments was higher than the control except for the larvae.