Bridging behavior and spatial propagation: a new double spiral maze and image analysis pipeline to study dispersal in groups of minute insects
Bridging behaviour and spatial propagation in minute insects: the double-spiralmethod and image analysis pipelineMélina Cointe, Vincent Calcagno, Ludovic Mailleret, Mathias Launay, Victor Burte, Guy PerezStudying what is difficult to observe, has always aroused the curiosity of human beings and fosteredmethodological innovations. Minute insects such as parasitic micro-wasps have high basic and appliedimportance, for their widespread use as biocontrol agents, but they are difficult to observe both in thelaboratory and in the field. Their dispersal i.e. their spatial spread that can have consequences on theirreproduction and gene flow is a phenotype of particular interest. Classically, the dispersal of suchinsects is studied using field releases, but those are time consuming, costly, and the results highlyvariable, preventing high-throughput and repeatability. Alternatively, dispersal can be studied in small-scale behavioural assays. However, those neglect important higher-scale processes such as groupdynamics. Consequently, proper evaluation of dispersal metrics is often complicated and lacking in thestudy of behavioural dynamics or, for example, biocontrol breeding programs. Here we introduce anew method, coupling a double spiral arena with computer vision aided insect counting andlocalization, which permits the study of spatial propagation at relevant scales (several hours andmeters), retaining high throughput and experimental power. The method records the location of everyindividual at high frequency, providing precise estimates of Mean Squared Displacement and diffusioncoefficients. This provides an affordable and easy-to-implement tool for studying insect movementand performing behavioural ecology, applicable to biocontrol research. We describe the method andapply it on 14 strains of a species of agronomic interest: Trichogramma cacoeciae, a parasitoid micro-wasp. Several experiments allowed us to identify two main types of spatial propagation dynamics. Oneis characterised by an initial phase of acceleration followed by a sustained diffusive regime. The otherby an initial phase of acceleration followed by a phase of slowing down.
Published : 2023-02-07