Toxic associations: A review of the predatory behaviors of millipede assassin bugs (Hemiptera: Reduviidae: Ectrichodiinae)

Ectrichodiinae (Hemiptera: Reduviidae), the millipede assassin bugs, are a speciose group (>660 species) of assassin bugs that appear to be specialist predators on Diplopoda, or millipedes. Apparently capable of coping with the noxious defensive compounds produced by many millipedes, Ectrichodiinae are engaged in a predator-prey relationship with millipedes realized only by few other arthropods. Unfortunately, feeding behaviors of Ectrichodiinae are inadequately documented, rendering this exciting phenomenon largely inaccessible. We here present a literature review on ectrichodiine prey selection and feeding behaviors, with supplemental original observations on Rhiginia cinctiventris (Stål, 1872) in Costa Rica. Thirteen species in 12 genera have been observed to feed on millipedes. The majority of diplopod prey species were reported from the orders Spirostreptida and Spirobolida, whereas Polydesmida are rarely attacked. Ectrichodiinae insert their stylets at the millipede's intersegmental membranes on the ventral and ventro-lateral trunk area or between the head and collum. Communal predation was observed among conspecific nymphs, among groups of nymphs with a conspecific adult, and more rarely among adults. Immature ectrichodiines were rarely observed to engage in solitary predation. Observations on R. cinctiventris indicate that this species preys on spirobolid and polydesmid millipedes and are in agreement with behaviors described for other Ectrichodiinae. [PUBLICATION ABSTRACT]