Plant material. Eight genotypes were studied: Solanum cheesmaniae (LA1412), Solanum peruvianum (Peru CMV) and six varieties of S. lycopersicum (747, Wooly, Yellow Bells, Clomimbo, Lancaster, Hairless). These genotypes were the same as those previously used for assessing the effects of trichomes on leaf, stem and petiole on T. urticae and T. (A.) recki (Tabary et al. 2024). To obtain the experimental plants, seeds were sown in plastic pots (8 x 8 x 8 cm) in a greenhouse (25 ± 2°C, 40 ± 30% RH) and watered twice a week until the beginning of the experiment (when plants reached three leaves).
Mite Material. The mite stock colony of T. (A.) recki was initiated from populations (50–100 specimens) collected on Phlomis fruticosa L. (lamiaceae) at Saint Clément-de-Rivière (Hérault, France, 43.694144, 3.851792) on July 2021. Predatory mites were reared following the process described by McMurtry and Scriven (1965), in rearing units constituted of plastic arenas (10 x 15 cm) deposited on moistened sponge support, surrounded by water-saturated paper tissue for avoiding mite escape. The population was maintained in a climatic chamber (25 ± 2°C, 16D:8N photoperiod, 70 ± 30% RH) and fed with commercialized Typha angustifolia pollen (Nutrimite®) twice a week.
Trichome characterization. The trichome characterization followed the protocol used by Tabary et al. (2024) on the same plant material. Briefly, a piece of 1 cm of stem between the second and third leaf was cut with a razor blade, and on two areas of 4 mm2 the types and number of trichomes were evaluated using a stereomicroscope (Nikon SMZZ1500 (x20)). Two replications were performed per plant, and 5 plants of each genotype were evaluated (in total 10 replicates / genotype). The trichome type classification proposed by Luckwill (1943) and Channarayappa et al. (1992) were used. The trichomes types I, IV, V and VI were considered separately, while types II and III were grouped together due to their similarity and the lack of studies demonstrating their role in arthropod resistance (McDowell et al. 2011). Trichome types VII and VIII were not taken into account due to their rarity on the eight genotypes studied.
Experimental design. A 5 cm stem piece, located between the second and third leaf, was cut with a razor blade and then disposed on wet cotton on a Petri dish. A bean leaf disc (2.5 cm diameter, cv. Contender) with pollen of T. angustifolia (Nutrimite®) was disposed at one extremity, whereas a small piece of black plastic was placed at the other extremity (Fig. 1). One young mated female of T. (A.) recki was then disposed on the plastic piece. Once the female has dispersed on the stem, the plastic piece was removed. At least 10 replicates were carried out for each genotype. The age of predatory females was the same for each replicate. Observations were carried out at four different times: 10 minutes, 25, 55 and 100 minutes after the predator introduction. At each observation time, the predator was filmed for 5 minutes (camera Leica EZ4 W) and several parameters were assessed during the video observations: (i) the success of stem crossing : number of predators reaching the bean leaf and not turning back, (ii) hesitation behavior : the number of times the mite goes on and turns back on the stem without totally crossing it, (iii) escape behavior: number of predators retrieved on the wet cotton support and (iv) the mobility vs immobility duration. At the end of the experiment, the females were mounted on slides in Hoyer’s medium. The mites were then observed using a microscope (Leica DLMB, Leica Microsystèmes SAS, Rueil Malmaison, France) (400 x magnification), and body dimensions were measured. The Dorsal Shield Length (DSL) was assessed by measuring the distances between the setae j1 and J5. Three Dorsal Shield Width (DSWs) were assessed: (i) at the fore hind part measuring the distances between the setae z4 (DSW1), (ii) at the median part measuring the distances between the setae s6 (DSW2) and (iii) at the backward part measuring the distances between the setae S5 (DSW3) (Fig. 2).
Typhlodromus (A.) recki body size phenotypes. Tixier et al. (2021) carried measurements of 91 females of T. (A.) recki collected on six plant species in France and in Italy. Among the characters considered, these authors measured the dorsal shield length and although the measurements were not taken at exactly the same positions on the body as in the present study, DSL (measured at the edge of the body tegument in Tixier et al. (2021) and between setae j1 and J5 in the present study) and DSW1 (measured at the edge of the body tegument at the level of setae z3 in Tixier et al. (2021) and between setae z4 in the present study), we decided to use this dataset to determine whether the populations under consideration had variable body sizes and the proportion of “small” individuals in each of these populations.
Statistical analyses. All analyses were carried out using R Cote Team (2021). ANOVA were carried out to assess the mean differences in mobility time and hesitation numbers between the Solanum genotypes and between the females that succeed to cross or not the stem. ANOVA were also carried out to determine based on the dataset of Tixier et al. (2021) differences in DSL and DSW1 between the populations of T. (A.) recki here considered. ANOVA was carried out using the Kruskal-Wallis test (package “rstatix”) followed by Dunn test when the data did not follow a Normal law and/or with different variances, overwise ANOVA tests (package “car”) followed by Newman & Keuls test (package “Agricolae”) were performed. A multifactorial analysis was used to assess the relationships between trichome numbers, mite body size and mobility time variables, using the packages “FactoMineR” and “factoextra”. Correlation tests (corr.test) were also carried out to determine the relationship between the three dorsal shield dimensions using the package “ggpubr”.