Table 1.

Suggested scenarios for the application of metacommunity theory to insect–symbiont systems, taking into consideration community definitions, the possible questions that could be addressed with each system, and outlining a potential experiment to test address the question

Scenario	Local community	Regional community	Question(s) addressed	Experimental outline	Metacommunity response variable
A (see also Figure 1)	Individual insect	Host insect community	How much horizontal transmission of bacteria between individual insects occurs over a single host generation? How do abiotic factors or variable parasitoid pressure influence horizontal transmission?	Introduce a target bacterium to a metacommunity of axenic insects, and sample them at the end of one host generation to see how much the target bacterium has spread via horizontal transmission	Individual insect microbiome (local community) diversity
B	One insect host species	Multiple insect host species	What barriers exist between species preventing horizontal transmission of symbionts? (e.g., Is coevolution of host and symbiont a predominant barrier preventing horizontal transmission from one host species to another?)	Experimentally, again with axenic hosts, one could introduce a symbiont in different ‘doses’ to determine the point where dispersal is sufficient to overcome natural dynamics	Microbiome (local community) diversity
C	One individual plant	Multiple plants of single or multiple species, with their insect pests and symbionts included	How does a spatially structured metacommunity change the dynamics of herbivore–symbiont dispersal? Metacommunity structured by the location of plants, with parameters changed relative to previous scenarios by plants not moving and having much longer life spans	Comparison of different plant spatial configurations with measures of herbivore density, the number of symbionts, and the dispersal of symbionts, as a result of the distance between plant‐associated communities	Diversity of insects and associated symbionts on a particular plant
D	All insects associated with one plant individual	All insects associated with multiple plant individuals	How much does pest dispersal facilitate symbiont movement between plants? This scenario is a combination of scenarios B and C, based on the coevolved barriers between insect species and their impacts on symbiont dispersal, and the plant‐focused spatially structured metacommunity	Dispersal measured as the movement of insect herbivores (e.g., aphids) between plants, and the subsequent impacts on symbiont dispersal within the metacommunity (see Brady et al., 2014; Frago et al., 2017 for the associations between symbiont, insect, and plant)	Diversity of insects and associated symbionts on one particular plant
E	One local site of a focal symbiont‐infected host species, and close relative species of the host	Multiple sites of the focal insect host, its symbiont, and closely related species	Which insect species does a biocontrol symbiont spread to within a wild community? Will other species in the microbiome of wild hosts facilitate establishment of Wolbachia? This is a specific application toward biocontrol efforts. The example presented is the attempt to use male‐killing strains of Wolbachia to reduce populations of the dengue fever mosquito (Aedes aegypti)	In this scenario, dispersal is a combination of the mosquito's movement, transmission of the symbiont, and establishment of the symbiont, measured over time and space by capturing individuals of A. aegypti (and closely related species) and measuring them for the used Wolbachia strain. This enables us to quantify dispersal distance over time, and simultaneously consider spillover events into other insects in the natural community	Insect microbiome diversity