About Scentless Plant Bugs

The Rhopalidae or scentless plant bugs are a cosmopolitan family of coreoid bugs comprising roughly 18 genera and 209 species. In Australia Soapberry bugs Rhopalidae includes Lepticoris spp. seed-eating predators of Australian plants in the family Sapindaceae, notably Alectryon spp. Along the eastern coast the long beaked form of Leptocoris tagalicus occurs on at least 10 plants including non-native environmental hosts Balloon Vine Cardiospermum grandiflorum and Golden Rain Tree Koelreuteria elegans. Inland, it has a shorter beak and occurs on Atalaya hemiglauca. Leptocoris mitellatus is found mostly in the southern half of the continent on Alectryon oleifolius.

Soapberry Bugs Leptocoris rufomarginatus

Leptocoris tagalicus

Adult Leptocoris tagalicus (coastal form) are usually orange-red and black with a long beak which they use to pierce the seed and inject salivary enzymes used to digest their food. Legs and antenna are black. The first specimen shown below was on a Rhodamnia rubescens. Note the long beak. L. tagalicus is similar to L. mitellatus, found further south, but has more uniform coloration and noticeably a more slender neck (anterior thorax) and head than does L. mitellatus. L. mitellatus is more polychrome, has more prominent red eyes, and is rather neckless. L. mitellatus spends a lot of time on the ground. This L. tagalicus grew up on seeds of the Alectryon tomentosus trees in Sherwood Forest Park. Shown are fifth (last) stage (instar) nymphs and their freshly molted fellows. They will remain densely aggregated for about a day after the moult, until their soft exoskeletons harden sufficiently to make walking safe and flight possible.

Leptocoris tagalicus adult beak

Leptocoris tagalicus adult. Photo: Robert Whyte

Leptocoris tagalicus adults and nymphs. Photo: Scott Carroll 

Leptocoris rufomarginatus

The genus includes L. rufomarginatus, a beautiful red-eyed bug with white sections on a brilliant red abdomen, and a silvery, blue-grey, green-grey section on its wings. L. rufomarginatus has been verified as feeding on Jagera psuedorhus, previously not confirmed as a host plant, in observations by Robert Whyte and Michael Mathieson in late November 2006 at Enoggera Creek The Gap adjacent to the cricket nets on the ovals of the The Gap State High School. Leptocoris rufomarginatus is an impressive bug. Compared with the other species, L. rufomarginatus is long-winged, narrow-bodied and a ready flier. It is relatively restricted to the far eastern and northern moist subtropics and tropics. When the bugs finish their last moult to become adults, they are bright red and soft. Scott Carroll writes: “This species is really quite volant and arboreal, [with a] streamlined, deep-bodied, long-limbed morphology … They are the most widespread soapberry bug – South-East Asia north to southern Japan, east all the way to the Tuamota Archipelago in the eastern Society Islands.” These bugs were on a Diospyros fasciculosa below their probably host plant Jagera pseudorhus. Scott Carroll writes: “We inspected Jagera pseudorhus for bugs between Northern Rivers and Cape York, and found none, but it has always looked like a good host to me … it is unlikely that these bugs have crawled far from where they fed.”

Leptocoris rufomarginatus adult. Photo: Robert Whyte

Leptocoris rufomarginatus adults. One of these adults is newly emerged. Photo: Robert Whyte

Leptocoris rufomarginatus adults and nymphs. Photo shows last instar nymphs and teneral adults. Photo: Mark Crocker 

The more mature adult has distinct colouration including the blue grey section of wing, and you can just see the white sides to the abdomen. These bugs are spectacular in flight, as the brilliant red abdomen is exposed. Photo: Robert Whyte 

Leptocoris rufomarginatus, surveying the possibilities from the outer edge of an Alectryon tomentosus leaf in Brisbane. Photo: Scott Carroll

An experiment was conducted to give some Leptocoris rufomarginatus access to Jagera pseudorhus fruit capsules and seed in a terrarium in an attempt to observe feeding. See more on this below. Photo: Robert Whyte

This photograph by Mark Crocker was taken of a nymph sheltering on a Diospyros fasciculosa under a Jagera pseudorhus. About two weeks previously a savage storm ripped through this area accompanied by heavy hail. This may have stripped the Jagera of bugs many of which where not yet flying adults. They are likely to to have walked to the nearest safe place, the flying adults moving to the Jagera to feed but often returning to be with the juveniles as they developed. Photo: Mark Crocker 

The blue pane of this bug’s wing must have some evolutionary advantage, perhaps to warn potential predators of the unpleasant taste garnered by feeding on cyanide collecting seeds of the Sapindaceae.

This photograph shows L. rufomarginatus feeding on seed of Jagera psuedorhus. The posture, beak deployment and general look of contentment are most consistent with feeding. Photo: Robert Whyte 

This photograph is definitive proof of L. rufomarginatus feeding on seeds of Jagera psuedorhus. The beak is penetrating the seed casing. The beak is a jointed tube (labium), with four long, narrow, flexible, chisel-tipped stylets within. They can be used as a seemingly unified structure, or sometimes the labium is partially folded back from the stylets. The stylets do the penetration and excavation. The labium houses also provides a channel for the expulsion of digestive saliva into the seeds, and the piping of the liquefied material back into the body with a suction pump apparatus in the mouth region. Photo: Robert Whyte

References

(1) Ecology of Leptocoris Hahn (Hemiptera: Rhopalidae) soapberry Carroll, Scott P; Loye, Jenella E; Dingle, Hugh; Mathieson, Michael; Zalucki, Myron P Australian Journal of Entomology, Volume 44, Number 4, November 2005, pp. 344-353(10)
Rapid evolution in Florida Soapberry Bugs Scott P. Carroll, Hugh Dingle, Thomas R. Famula & Charles W. Fox Genetica 112-113: 257-272, 2001 © 2001 Kluwer Academic Publishers. Printed in the Netherlands.
And the beak shall inherit – evolution in response to invasion Carroll, Scott P.; Loye, Jenella E.; Dingle, Hugh; Mathieson, Michael; Famula, Thomas R.; Zalucki, Myron P., Ecology Letters, Volume 8, Number 9, September 2005, pp. 944-951(8)