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.
Highlights
Millipedes (Diplopoda) are a diverse group of arthropods that include 16 orders represented by approximately 12,000 species in 145 families (Sierwald & Bond, 2007)
In 11 of these orders, millipedes are protected from predators by chemical defenses produced in glands that vary in number among orders and are located laterally or mid-dorsally in the diplosegments (Eisner et al, 1978; Hopkin & Read, 1992)
Some invertebrates are specialized predators or parasitoids on juliform millipedes (Banks, 1911; Picard, 1930; Lawrence, 1984; Eisner et al, 1998; Dejean et al, 2001; Brunke et al, 2009; Larsen et al, 2009). None of these groups of millipede specialists are speciose. This is dramatically different in the Ectrichodiinae, the fifth largest subfamily of Reduviidae (Hemiptera: Heteroptera), or assassin bugs, that appears to be specialized on millipedes (Green, 1925; Haridass & Ananthakrishnan, 1980; Haridass, 1985)
Summary
Millipedes (Diplopoda) are a diverse group of arthropods that include 16 orders represented by approximately 12,000 species in 145 families (Sierwald & Bond, 2007). We compile published data and evaluate images available on the Internet for prey specificity, point of stylet insertion, and communal predation. Data for Rhiginia cinctiventris (Stål, 1872) are presented based on observations in the field and laboratory at one site in Costa Rica; feeding observations have never been reported for this genus before.
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