A New Method to Prevent the Individuals of the Predatory Mite, Amblyseius swirskii Athias-Henriot (Acari: Phytoseiidae), from Exiting the Area Allocated to them in the Laboratory

The generalist predator mite, A. swirskii, has a high prey consumption capacity (Fathipour et al., 2017). Several studies were conducted in the laboratory to develop its usage. Vázquez-Benito et al. (2022) studied the combined application of it and fungal pathogens for biological control of mite pests under laboratory conditions.

Crucial measures have to be taken to avoid the mite escaping while rearing it. Closed containers may be necessary, especially while dealing with flying insects. To observe the mites placed on bean leaflets with abundant prey, Nguyen and Amano (2009) placed each leaflet on a strip of filter paper; each filter strip was inserted into a small transparent plastic vial. The top of the vial was covered with a polyvinyl sheet and fastened shut with a rubber band to prevent the mites from escaping. Messelink et al. (2011) tested the effect of the predatory mite A. swirskii on aphid populations. For this, leaf discs were embedded in water agar, each in a separate plastic box. The mites and the insects were placed on the leaf discs. Wu et al. (2018) used Tetranychus urticae Koch mites to feed predatory mites on excised kidney bean leaves placed on black plastic mulch in a covered plastic container. A hole was cut in the lid and covered with fine mesh to provide ventilation. Parkand Lee (2020) reared mite individuals in Petri dishes with a nylon-mesh-covered hole in the lid.

For better detection, open containers such as Petri dishes may be preferable to closed ones, but appropriate measures must be taken to prevent the mites from escaping. Baier and Moll (2002) conducted a bioassay using bean leaf discs that were surrounded by a glue barrier to prevent mite escape. Bostanian et al. (2009) modified a method based on leaf discs that fit tightly into the bottom halves of Petri dishes. The top half of each Petri dish had a window. For phytophagous mites, the window was covered with a Pecap polyester screen. That method reduced losses due to escapees and allowed observations to be made. Nguyen et al. (2015) reared phytoseiid mites on green plastic arenas placed on a wet sponge in a plastic tray containing water. The edges of the arenas were covered with tissue paper immersed in the water to provide moisture and deter the mites from escaping. However, some mites were able to escape. Kakkar et al. (2016) created an experimental arena consisting of a Petri dish lined on the bottom with a thin layer of moist cotton wool. A cucumber leaf disc was placed in the center of the Petri dish onto which a mite individual and larvae of thrips were released. Gyuris et al. (2017) placed mites in plastic cups on bean leaf discs on wet cotton to prevent them from leaving. Fathipour et al. (2019) covered the margins of Petri dishes with paraffin layers to prevent mites from escaping. Schausberger et al.(2020) reared A. swirskii on artificial arenas. Each arena consisted of an acrylic resting on a water-saturated foam cube in a plastic box half-filled with tap water. The edges of the tile were surrounded with moist tissue paper to prevent the mites from escaping.

A cost-effective method for mass-rearing of phytoseiid predatory mites is an essential prerequisite (van Lenteren, 2003).

While rearing predaceous mites in laboratories, many individuals get lost due to escaping or sticking to the surrounding barrier. On the other hand, mite dispersion in the laboratory is considered undesirable. The present study has presented a solution to that problem. By applying the new method, it would be more prosperous to rear the predatory mite, A. swirskii, for study or for commercial purposes. Most studies depend on using water as an escape inhibitor. The present study dealt with different kinds of liquids to determine the most effective one as an escape inhibitor.

MATERIALS AND METHODS

Source of mites

Individuals of the predatory mite A. swirskii were obtained from cotton leaves. They were transferred gently from the leaves by using a thin brush with a little sodden hair. By using a water-saturated brush, mite pickup is easy.

Preventing the mites from escaping

A hermetic barrier has to be set up to prevent the mites from escaping. For this, four main methods were carried out, three of which involved placing a liquid in a groove located along the margin of a 13-cm-diameter round plastic dish; the middle part of the dish was allocated to the mites. Meanwhile, the fourth method involved placing a liquid in a Petri dish into which a table-shaped unit was put; the table board was allocated to the mites.

1. Placing a liquid in a groove located along the dish margin

     Round plastic dishes (13 cm in diameter) were utilized to carry out three of the main methods. Each dish had a groove along its margin. The grooves were allocated to the liquids.

The three main methods were distinguished as follows:

1. 1. Without laying a thread around the area allocated to the mites

      As shown in Fig. 1, no thread was laid on the dish surface.

1. 2. Besides laying a thread around the area allocated to the mites

As shown in Fig. 2, a 0.2-mm-diameter cotton thread was laid around the area allocated to the mites. One of the thread tips was immersed in the liquid located in the groove to ensure continuous saturation. There was a narrow space between the thread and the surrounding groove.

1. 3. Besides erecting a wall around the area allocated to the mites and laying a thread on the wall top

As shown in Fig. 3, a 5-mm-high wall was set up around the area allocated to the mites. The wall worked as a fence. The wall was erected by using a hot melt glue stick and an electric gun. There was a narrow space between the wall and the surrounding groove. A 0.2-mm-diameter cotton thread was laid on the outer bevel of the wall top. One of the thread tips was immersed in the liquid located in the groove to ensure continuous saturation. A cross section of the thread located on the wall top is illustrated in Fig. 4.

2. Placing a liquid in a Petri dish into which a table-shaped unit is put

As shown in Fig. 5, a table-shaped unit was made. The table board was represented by a foam cuboid. It was 3 cm long, 1 cm wide, and 1 cm high. The table legs were represented with wooden parts of matches. Each leg was 3 cm tall. A small part of each leg was inserted into the foam for fastening. The unit was placed in a Petri dish in which a liquid was put. The liquid was 1 cm high.

Liquids used, and the total number of ancillary methods tried out

As regards each of the four above mentioned methods, four main liquids were utilized with the aim of estimating their comparative efficiency as escape inhibitors. Two of the liquids were used at different concentrations. Hence, a total of 12 liquids were utilized for each of the four main methods. The 12 liquids were water; camphor oil; phosphoric acid at the concentrations of 1, 2, 3, 4, and 5%; and citric acid at the concentrations of 5, 10, 15, 20, and 25%. Thus, a total of 48 ancillarymethods were tried out.

Three replicates were used for each of the 48 ancillary methods.

Placing the mites and detecting them

After taking the measurers of escape prohibition, 100 mite individuals were used for each replicate. As regards the methods involving placing a liquid in a groove, mites were placed in the middle of the dish. As regards the methods involving placing a liquid in a Petri dish, mites were placed on the cuboid representing the table board.

All experiments were conducted at a temperature of 30 ± 5° C, a relative humidity of 70 ± 5% and a 16:8 hrs. (L: D) photoperiod. 

Inspections were done in 24 hours. The mite individuals that managed to pass across the thread were counted; the average percentages of them were calculated. The mite individuals that drowned in the liquids, or stuck to the thread were counted; the average percentages of them were calculated.

Statistical analysis

Data were analyzed using ANOVA and ″F″ Test, with 3 replicates for each treatment. The least significant differences (L.S.D.) at the 0.05 ≤ level were determined according to the computer program CoStat software and Duncan's Multiple Range.

RESULTS

Average percentages of the mites which managed to pass across the barrier 

No mite individual could pass across the liquids located in the grooves or in Petri dishes. As regarding using a liquid-saturated thread to prevent mite escaping, as shown in Table (1), no mite individual could pass across the thread saturated with any of the following liquids: camphor oil; phosphoric acid at the concentrations of 3, 4 and 5%; or citric acid at the concentrations of 15, 20 and 25%. Some individuals were able to pass across the thread saturated with the other liquids, but the liquid existing in the surrounding groove prevented the mites from escaping and being lost. The highest average percentage of the miteswhich managed to pass across the thread was 4.33%; it was attained by applying the wall-based method, using water as an escape inhibitor.

Table 1 Average percentages of mite individuals which managed to pass across the liquid-saturated thread   

The experiment was based on three replicates.

Averages followed by the same letter are not significantly different at P < 0.05 level.

Ranks are arranged in descending order.

Average percentages of the liquid-adhered mites

As shown in Table (2), some mite individuals adhered to the liquids. In other words, some individuals drowned in the liquids; others stuck to the liquid-saturated thread. Whatever liquid was used, the wall-based method indicated the lowest average percentage of the liquid-adhered mites. As far as the 48 methods are concerned, the lowest average percentage of the liquid-adhered mites, 0.33%, was attained by applying the wall-based method, besides saturating the thread with phosphoric acid 3%. On the contrary, the highest average percentage of the liquid-adhered mites, 7%, was attained with applying the method involving surrounding the area allocated to the mites with a groove and filling it with citric acid 25%.

Table 2 Average percentages of the liquid-adhered mites

The experiment was based on three replicates.

Averages followed by the same letter are not significantly different at P < 0.05 level.

Ranks are arranged in descending order.