Investigating chemical communication in oribatid and astigmatid mites in bioassays - Pitfalls and suggestions

Abstract

A pair of exocrine opisthonotal oil glands from which more than one hundred chemical compounds have been described characterizes the glandulate Oribatida and the Astigmata. While allomonal and pheromonal properties were demonstrated for some of these compounds in some species, the biological function has remained unknown in most cases. The few existing studies on chemical communication used different kinds of experimental designs with bioassays and impregnated filter paper as source for scent dispersal. Like this, the existence of alarm-, aggregation- and sex-pheromones has been demonstrated. Here, we show that most of these studies may have suffered from some shortcomings regarding two parts of the experimental design: i) proper replication and ii) source for scent dispersal. Hence, this contribution has two principle parts: in the first part we focus on bioassay design and the occurrence of pseudoreplication by analyzing published studies with astigmatid and oribatid mites in a literature survey. The second part concerns the source for scent dispersal used in bioassays: we investigated the evaporation dynamics of multi-component-secretions from paper and paper/clay combinations and show that these represent two different principal kinds of sources (instantaneous vs. continuous release of scents). Paper alone is an improper source for long-standing bioassays (i.e. several minutes) because different compounds evaporate with different rates leading to a dramatic change in relative composition. This is much less pronounced in a paper/clay combination.

Keywords

• chemical ecology
• pseudoreplication
• bioassay
• emitting source
• diffusion
• Oribatida