Source of the mite
Cotton leaves were the source of the mite A. swirskii. A thin brush with a little sodden hair was used to transfer the mites gently from the leaves; saturating the brush hair with water makes it easier to attach the mites to the brush hair for successful pickup. Obtained mite individuals were kept without food for 24 h before starting the experiments.
Preparing the food stuffs
In previous studies, the effect of certain nutrients on the life aspects of predatory mites were assessed regardless of the nutrient properties. For example, Etienne et al. (2021) mentioned that food supplementation promotes predatory mites and enhances pest control. However, they didn't estimate the stickiness of almond pollen they used. The commonly manipulated nutrients were considered in the present study. Hereupon, the tested nutrients were evaluated into two main categories:
Skim milk 0.5% fat, honey, yolk, baker's yeast Saccharomyces cerevisiae, amino acid solution 10%, whole milk, albumin, grape juice, sugar cane juice, water, chicken blood, smashed cow liver, living and smashed drosophila eggs, living and smashed drosophila larvae, living and smashed drosophila pupae, cotton pollen, maize pollen.
Drosophila melanogaster was reared in the laboratory on smashed grape in Petri dishes to get its immature stages. The tip of a piece of cloth was dipped in the smashed grape, whereas the other wet tip was kept out of the smashed grape for egg laying. Larvae were obtained from the smashed grape, whereas the pupae were obtained from the surrounding dry area. Obtained drosophila eggs, larvae, and pupae were rinsed with water and dried with paper tissue before being presented to the mites as food. Some individuals of each drosophila stage were smashed severally before presenting to the mites as food.
Mixtures of nutrients
Mixtures of skim milk 0.5% fat, honey, yolk, baker's yeast and amino acid solution 10% at the volume ratios of (100:1:1:1:1), (100:10:1:1:1), (100:20:1:1:1), (100:1:10:1:1), (100:1:20:1:1), (100:1:1:10:1), (100:1:1:20:1), (100:1:1:1:10), (100:1:1:1:20).
Thereupon, each of the components honey, yolk and baker's yeast was used in the mixtures at the percentages of 0.96, 8.85 and 16.26%. However, the percentage of each component wasn't exaggerated in order not to have a mixture similar to the absolute component, which is examined individually as a single nutrient.
Estimating the parameters of the nutrient suitability
Estimating the attractiveness and the stickiness
Three replicates were established to examine the nutrients. For each replicate, 300 mite individuals were placed in a plastic dish (10 cm in diameter), which had a surrounding groove full of camphor oil to prevent the mites from escaping. A drop of about 0.02 ml. of each liquid nutriment was added in each replicate. As for living and smashed drosophila stages, 5 eggs, 3 larvae and one pupa were used for each replicate. As for pollen, a pile of about 50 individuals of each kind was used in each replicate. The space between each nutriment and the adjacent one was about 0.5 cm. After adding all nutrients, mite groups at the dish edges were aroused with a brush tip to move. All experiments were conducted at a temperature of 30 ± 5 °C, relative humidity of 70 ± 5% and a 16:8 h. (L: D) photoperiod.
Numbers of the congregating mites, in 2 min, to feed on a nutriment, and numbers of the stuck ones to it, within two minutes, were recorded. The percentage of the mites congregating to feed on a nutriment, in relation to the total feeding mites in the same replicate, was calculated. Moreover, the percentage of the mites stuck to an edible nutriment, in relation to the congregating mites feeding on it was also calculated.
As regards the most attractive mixture, i.e., the mixture of milk, honey, yolk, baker's yeast, amino acid solution 10% at the ratio of 100:1:1:20:1, respectively, it was preserved in the fridge for 1, 2, 3 and 4 days, and presented to the mites to estimate its maximum edibility span after preserving.
Estimating the edibility span
The maximum edibility span of each edible nutriment was estimated. Five starved mites, which were kept for 24 h. without food, were introduced to each edible nutriment at different successive times and replicated 3 times. Nutriment mite-neglecting, for 2 min, was an indicator that the nutriment was no longer edible. Solidification of the surface of some edible liquid nutrients, which makes it too solid to feed on and allows the mites to walk on it without sticking, was another indicator that the liquid nutrient is about to be inedible. As regards maize pollen and grape juice, edibility checks were done every hour. As regards the rest of the edible nutrients, an edibility checkup was done every minute. The five mites were exchanged with others, which were kept for 24 h. without food, for each checkup.
The data were analyzed using ANOVA and the “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. A correlation between the percentage of each of honey, yolk and baker's yeast, and each studied property of the edible mixtures was calculated.