Fresh A. vera L. leaves were collected, chopped into small pieces, placed in an oven, and dried at 50˚C. The leaves were then pulverized into plant powder using a by crusher. The plant powder was weighed and placed in a 10 L grinding mouth bottle. The plant powder was immersed in 100% acetone with 1 g of ground material and 5.0 mL of acetone while intermittently shaking. The acetone extract was filtered and evaporated at 50˚C using a vacuum rotary evaporator. The plant extract was transferred in Petri dishes. The extract was washed three times and stored in a refrigerator at 4˚C until use.

The mites used were from a T. cinnabarinus population sampled from young cowpea plants (Vigna unguiculata) in Beibei District, Chongqing, China. The mites were maintained in potted young cowpea plants in a laboratory at 26˚C ± 1˚C, 75% - 80% relative humidity (RH), and 14 h light/10h dark cycle with no acaricide exposure for more than 13 years. Voucher specimens, as part of an insect collection, were deposited at Southwest University.

Analytical-grade acetone was purchased from Chengdu Kelong Chemical Reagents Co., Chengdu, China. Tween-80 F was purchased from Jiangsu Haian Petrochemical Plant, China.

The immersion method recommended by FAO [6] was used to examine the acaricidal activity of the acetone extract from A. vera L. against T. cinnabaribus engorged female adults. Double-sided adhesives were cut into 2 cm-long pieces and stuck to one end of the slides. A total of 35 female adult mites, which were uniform in size, color, and brightness, were stuck on their back onto double-sided gum (which does not stick onto mite feet, antennae, and mouth) using a zero brush. They were bred on the cushion of a wet sponge white disk and for 4 h before examination under a stereomicroscope (4× magnification). Then, some dead and unhealthy mites on the slides were removed.

About 5.00 mg of extract was mixed with and completely dissolved in a certain amount of acetone. Then, A 0.1% Tween-80 [7] was added to the mother aqueous solution, which was diluted into different concentrations (2.50, 1.25, 0.635, 0.3125 mg/mL) with water controls against T. cinnabarinus adults. The treatments were performed by dipping the slides with mites into each extract solution for 5 s. Any extra solution on the slides was carefully absorbed with filter paper after treatment. The controls were dipped in water only; they were subjected to the same conditions of 25˚C ± 1˚C, 65% - 80% RH, and 14 h light/10h dark photoperiod for 3 days. The mites were considered dead if their movement was imperceptible after repeated gentle probing with a fine brush. Mortality was assessed under a binocular microscope every 24 h. [8].

Based on the method of Hussen et al. [9], fresh cowpea seedling leaves were placed in Petri dishes. Half of the leaf surface was carefully wiped with treatment reagent; the other half was wiped with the same proportion of leaf solvent control. After the solution dried, 20 female adult mites were collected from each leaf. Each treatment was repeated three times. The number of repellency was assessed under a binocular microscope after every 12 h for 4 days. The repellency rates were calculated as follows:

Based on the fumigate method of the tin method [10] with minor modifications, 20 female mites on each leaf were fresh cowpea seedlings. Leaves with mites, the absorbent cotton, and the filter in Petri dishes were placed in a 100 mL tin bottom. Then, three lethal concentrations of the leaf acetone extract to 30% (LC₃₀), 50% (LC₅₀), and 70% (LC₇₀) of adults were injected. The same proportion of the solvent controls was also injected into the filter paper of the bottle caps as soon as the bottle caps were covered. The bottles were then moved into artificial climate indoors. Before observation, the bottle was kept open for 1 h, and the mites along with the cotton filter paper were removed for observation every 24 h. The mortality of the female mites was recorded. For each application, 15 replicates were tested. Continuous observation was conducted for 5 days. After the experiment, the corrected mortality was calculated as follows:

The leaf disk method was used to evaluate the oviposition inhibition activity of female carmine spider mites. Leaves from young cowpea plants, filter paper, and absorbent cotton were placed in Petri dishes. The back of leaves was carefully wiped with different concentrations of treatment reagent using swabs. Another three Petri dishes were set at the same proportion of solvent solution for comparison. After the solution dried, 20 female adult mites were collected from each leaf. The numbers of mites in the extract-treated and non-treated areas were counted every 12 h post-treatment under a stereomicroscope (4´ magnification). The experiment lasted for 6 days. When the experiment was finished, the oviposition inhibition rate was calculated as follows:

where NE is the number of eggs laid.

All mortality results were corrected using Abbott’s formula  in terms of the aloe acetone extracts with control. The data were analyzed with one-way ANOVA followed by Tukey’s multiple range test at P < 0.05 using SPSS 17.0 software. The LC₅₀ and LC₉₉ values, as well as their respective 95% confidence intervals (CIs), were calculated by probit analysis (Polo Plus software). The repellent and oviposition inhibition rates were analyzed with software of Microsoft Excel 2003 and SPSS 17.0.

The aloe acetone extract showed strong contact acaricidal activity against T. cinnabarinus female adults (Table 1). The LC₅₀ was 0.836 mg/mL, and the 95% CI ranged from 0.716 mg/mL to 0.964 mg/mL. The LC₃₀, LC₅₀, and LC₇₀ values were calculated at different processing times (Table 2). At 48 h after treatment, the LC₃₀, LC₅₀, and LC₇₀ values were 0.473, 0.836, and 1.476 mg/mL. These three concentrations were used to measure the fumigant, repellent, and egg laying inhibition activities of the aloe acetone extract against T. cinnabarinus female adults.

The repellent rates after treatment for 96 h were obtained from the LC₃₀, LC₅₀, and LC₇₀ values of the aloe acetone extract against T. cinnabarinus female adults. Figure 1 shows that after treatment for 12 h, remarkable repellent activities at the LC₃₀, LC₅₀, and LC₇₀ values were observed. After testing for 12 and 48 h, the mites’ rate of treatment reached 50%. The repellent rates at the three concentrations showed more fluctuations with the processing time. With increased processing time, the repellent rates of LC₃₀, LC₅₀, and LC₇₀ showed lower rates than that after 12 h of testing. The female carmine spider mites may control eating when food is abundant. However, under food shortage, the mites feed in other areas to guarantee their survival. At LC₅₀ and LC₇₀, low mortality was observed, which also explained the gradual decrease in the LC₅₀ and LC₇₀ values. In summary, the acetone extract of A. vera L. leaf had some repellent effect against T. cinnabarinus.

The LC₃₀, LC₅₀, and LC₇₀ values of the aloe acetone extract were determined. The corrected fumigating morTable 1. Toxicity regression line of the acetone crude extract from Aloe vera L. against Tetranychus cinnabarinus female adults in the laboratory.

Table 2. Lethal concentrations (in mg·mL⁻¹) of the acetone crude extract from Aloe vera L. against Tetranychus cinnabarinus female adult in the laboratory.

Note: LC₃₀, LC₅₀, and LC₇₀ are the lethal concentrations that killed 30%, 50%, and 70% of T. cinnabarinus. Each extract solution had five concentrations, and tests were replicated three times. The control solution comprised water with 1% Tween-80. P < 0.05 (ANOVA, followed by Duncan).

tality increased with increased concentration of aloe acetone extract (Figure 2). The maximum LC₇₀ value fumigating mortality rate against T. cinnabarinus adults reached 39.39%, which also indicated that the LC₇₀ value of the aloe acetone extract against T. cinnabarinus adults for 120 h. The average corrected fumigating mortality rates reached 32.88%. The average corrected fumigating mortality rates for LC₃₀ and LC₅₀ were 15.92% and 27.18%. In this experiment, the symptoms of mite death were their clinging back to cowpea leaves, pointed-up feet, and limb stiffness. Although the fumigating mortality rate slightly differed with prolonged processing time, the fumigating mortality result was not significant. The fumigating mortality rate was generally below 40% based on the overall results. Thus, the three concentrations of Aloe vera acetone extract against T. cinnabarinus adults under the same test conditions had minimal fumigating activity.

The result of the oviposition inhibition activity was obtained from the LC₃₀, LC₅₀, and LC₇₀ values of the acetone extract of A. vera L. leaf against T. cinnabarinus female mites (Figure 3). The oviposition inhibition rate of LC₃₀ decreased with prolonged processing time. The concentration of the oviposition inhibition rate effect was not significant. For the LC₃₀, LC₅₀, and LC₇₀ values, the average oviposition inhibition rates were 1.83%, 27.50%, and 62.86% for 6 days. The LC₃₀ and LC₅₀ values had some oviposition inhibition activity; however, the activity was low. Especially after 84 h, the oviposition inhibition activity of LC₃₀ was not obvious. LC₇₀ showed that the acetone extract of A. vera L. had a significantly higher oviposition inhibition activity against T. cinnabarinus adults, and the highest oviposition inhibition rate reached 83.33%. The aloe acetone extract against the cinnabar of female adult mites had a certain spawning inhibited activity. In summary, the acetone extracts of A. vera L. had some oviposition inhibition activity against T. cinnabarinus adults. However, the activities were not very strong and cannot last for a long time.