Harmonic radar tracking of tephritid fruit flies: Individual fly observations, movement parameterization, and modeling

The development of small harmonic radar (HR) tags has enabled tracking mid-sized highly mobile insects such as tephritid fruit flies.  Key to tracking such insects is fabricating tags with antennas made of superelastic nitinol wire resulting in a tag that is light (weighing as little as 350 μg), flexible, and does not tangle. Tracking tagged flies is an enhancement of previous approaches used to quantify insect movement (such as mark-release-recapture, flight mills, and visual observations) because it allows the researcher to observe individual fly movements in nature, mirroring studies conducted by ecologists on larger animals. We have successfully conducted HR tracking experiments with three tephritid species (Zeugodacus cucurbitae, Bactrocera tryoni, and B. jarvisi) in Hawaii and Australia in diverse environments including large field cages, papaya fields, and open parkland.  Movement parameterization showed non-random turning angles in all experiments indicating flies have a strong bias toward continued “forward” movement.  Multiple experiments also show that tephritid flight directions are correlated with wind direction, that movement parameters vary for within- and between-tree flights, and that step-distance distributions are consistent with Lévy walks. We used movement parameters derived from tracking to model tephritid dispersal using simple random walk, correlated random walk, and hidden Markov models. Movement data from these studies may help enhance current surveillance, control, and eradication methods, such as optimizing trap placements and pesticide applications, determining release sites for parasitoids, and setting quarantine boundaries after incursions.