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

Abstract

Abstract. 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.

The chemical defenses of millipedes (diplopoda): Biochemistry, physiology and ecology

“…According to Forthman and Weirauch (2012), all 600 or more species of Etrichodiinae in 123 genera appear to be millipede specialists (Fig. 19).…”

“…Rhiginia cinctiventris, the species they studied in Costa Rica, is conspicuously aposematic, as are many other etrichodiines, but the nature of their own chemical defense remains unknown. Forthman and Weirauch (2012) speculated that it might be possible the bugs sequester the defensive chemicals of the millipedes.…”

Assassin Bugs (Reduviidae Excluding Triatominae)

“…For example, Ectrichodiinae seem to be specialized to prey on millipedes (Cachan 1952 ;Forthman and Weirauch 2012 ), several taxa are termite predators, e.g., Salyavatinae (McMahan 1983 ), and one species of Harpactorinae-Apiomerini, Micrauchenus lineola (F.) (Bérenger and Pluot-Sigwalt 2009 ); species of Holoptilinae prey on ants (Jacobson 1911 ) and certain Emesinae and Harpactorinae on spiders (Wignall and Taylor 2008 ;Jackson et al 2010 ). Additional preferences, some of them tentative, are summarized by Ambrose ( 2000 ).…”

Morphology, Ontogeny, Reproduction, and Feeding of True Bugs

“…Although many Reduviidae appear to feed on a wide variety of arthropods, they sometimes show prey preferences or even prey specializations (see summary in Hwang and Weirauch 2012 ). Some of these preferences include millipedes (Cachan 1952 ;Forthman andWeirauch 2012 ), termite predators (McMahan 1983 ), ants (Jacobson 1911 ), spiders (Wignall and Taylor 2008 ;Jackson et al 2010 ), and other reduviids (Bérenger and Pluot-Sigwalt 2009 ).…”