A modified Munger cell for testing long-term effects of predator-induced stress on prey: an example using Tyrophagus putrescentiae (Acaridae) and its predator Neoseiulus cucumeris (Phytoseiidae)

Predators can influence prey directly by consuming them, or indirectly by inducing stress to them (Lemos et al. 2010; Dias et al. 2016). In studying non-consumptive effects, prey individuals are typically presented with the predator’s imprint or odour without direct contact. In such studies, experimental containers were exposed to predators or the animals of the experimental species for a short period (e.g. 24 or 48 h); the experimental species were then placed in these containers with the predator imprint/odour, which could induce stress or fear in the experimental species when they perceived the cues left by the predators (e.g. Mirza et al. 2006; Vidal-Gomez et al. 2018; Liu et al. 2019). The cues of some predators (e.g. ants) can also be presented to prey by smearing the extracts of predators on experimental discs (Lucas et al. 2018). Most studies of non-consumptive effects on mites involve phytoseiids and their phytophagous prey; the predators are placed on leaves for a short period (e.g. 24 h), and then the leaves with the imprint/odour of the predators are presented to the prey (e.g. Grostal & Dicke 1986; Oku et al. 2003; Škaloudová et al. 2007; Choh & Takabayashi 2010; Freinschlag & Schausberger 2016; Li & Zhang 2019). In a recent study we extended this research to phytoseiids feeding on stored product mites and showed that Tyrophagus putrescentiae could avoid cells with cues previously exposed to its predator Neoseiulus cucumeris or with prey killed by the predator (Wei & Zhang 2018). However, the effects were short-term (1–6 h) and the response was no longer significant after 24 h. In this and previous studies, the exposure of leaves or containers to predators is short term and the replacement of such predator-exposed units for any long-term experiments is laborious. In addition, the frequent transfer of mites to new leaves or containers with fresh predator imprint/odour can cause unnecessary damages to the mites. This study aims to establish a new method to enable continuous predatorinduced stress to prey by using a modified Munger cell, with T. putrescentiae and its predator N. cucumeris as an example. The culture of the two mite species was established from mites purchased from Bioforce Limited in South Auckland. The colonies were kept in plastic containers (14.5 cm × 14.5 cm) maintained in the laboratory (25 ± 2°C, 80 ± 2% RH, 16: 8 (L: D) using yeast as food for T. putrescentiae (see Li & Zhang 2016 for details). The experimental arenas for the prey and predators were created by using a modified Munger cell consisting of three plexiglass slides (25 mm wide, 38 mm long, and 3 mm thick), with a coneshaped hole serving as an arena (top diameter 9 mm and bottom diameter 7 mm) in the middle for the second slide (Fig. 1). The base of the second plexiglass slide is covered with a mesh cloth (500 grids per square inch), and the top is clamped with top plexiglass cover of the same size without the cone-shaped hole, to keep the storage mites inside the prey arena. The arena for the predators was a plexiglass slide of the same size, with a cone-shaped hole (top diameter 9 mm and bottom diameter