Phoretic Dispersal of Armored Scale Crawlers (Hemiptera: Diaspididae)

Abstract

Dispersal and colonization of new areas by armored scale insects (Hemiptera: Diaspididae) is achieved by mobile first-instar nymphs, called crawlers. Few studies have considered the actual mechanisms by which crawlers disperse, and although crawlers are capable of actively wandering over short distances (generally < 1 m), their dispersal over longer distances has been thought to be wind-mediated. Here, we present evidence of a potentially more important means of dispersal over longer distances (> 1 m). We first confirmed that crawlers of four species of Diaspididae [Abgrallaspis aguacatae Evans, Watson & Miller; Hemiberlesia lataniae (Signoret); Aspidiotus nerii Bouché; and Diaspidiotus perniciosus (Comstock)] have four hairs on the end of each of their legs and that each of these hairs ends in a suction cup-like structure, reminiscent of the attachment structures possessed by phoretic mites. In a controlled environment, using crawlers of A. nerii, we then showed that the crawlers use these structures to attach themselves to three different insect species [Musca domestica L., Cryptolaemus montrouzieri Mulsant and Linepithema humile (Mayr)] and can effectively be moved phoretically by these insects. Crawlers can remain attached to flying insects for considerable periods of time, suggesting that this may be an important means of dispersal for armored scale insects. The importance of phoresy for diaspidid dispersal in the field remains to be determined.

Crapemyrtle Bark Scale: A New Threat for Crapemyrtles, a Popular Landscape Plant in the U.S.

“…Under experimental conditions, birds were capable of transferring nymphs of the hemlock woolly adelgid, Adelges tsugae (Annand) (Hemiptera: Adelgidae) by touching infested branches [35]. Crawlers of four armored scales, including Aspidiotus nerii Bouche (Hemiptera: Diaspididae), Abgrallaspis aguacatae Evans, Watson & Miller, Hemiberlesia lataniae (Signoret), and Diaspidiotus perniciosus (Comstock), were found possessing a suction cup-like structure on hairs at the end of each leg, which can help them latch on larger insects to disperse [36]. We suspect A. lagerstroemiae could use larger animals to disperse.…”

Non-volant modes of migration in terrestrial arthropods

“…However, crawlers of some Diaspidid scales appear to use phoretic migration and have specialised attachment structures on the end of their legs [137]. It was suggested that phoresy may be more adaptive (because it was less risky than wind dispersal) in species which colonise patchily-distributed host plants and which have relatively low fecundities [137].…”

“…However, crawlers of some Diaspidid scales appear to use phoretic migration and have specialised attachment structures on the end of their legs [137]. It was suggested that phoresy may be more adaptive (because it was less risky than wind dispersal) in species which colonise patchily-distributed host plants and which have relatively low fecundities [137]. A remarkable form of phoretic dispersal occurs in the gall-forming genus Cystococcus (family Eriococcidae) whereby the minute female crawlers are transported out of the maternal gall, and on to nearby host plants, by clinging to the modified abdomens of their adult (winged) brothers [138].…”

Are some prepupae and pupae of male mealybugs and root mealybugs (Hemiptera, Coccoidea, Pseudococcidae and Rhizoecidae) mobile?

“…As far as we know, digitules are present in all first-instar nymphs or crawlers, the main dispersal stage. It has been shown that first-instar nymphs of some armoured scale insects (Diaspididae) attach themselves to their phoretic hosts (Diptera and Coleoptera) by the digitules (Magsig-Castillo et al 2010). These authors suggest that the swollen ends of each digitule can cling by suction.…”