Fig. 1. The specimen of Euoniticellus intermedius (Reiche, 1849) from Honduras in the collection of the Manchester Museum. © Roisin Stanbrook.
In November 2017, the Manchester Museum acquired a specimen of a very interesting dung beetle – Euoniticellus intermedius (Reiche, 1849) (see Fig. 1) – collected from Honduras by Roisin Stanbrook, a young researcher from the Metropolitan University of Manchester who studies the ecology of dung beetles in Central Africa (see here for her interview). In Honduras, Roisin was running a field course for a group of British students, when she came across this beetle which she was familiar with from her fieldwork in Kenya. What a surprise! Below is a brief account of how this dung beetle species appeared in Central America.
E. intermedius is also known as the Intermediate Sandy Dung Beetle. It is a medium sized (6.5-9.5 cm long) species of the burrowing dung beetles that build brood chambers in the soil beneath a dung pat and supply them with dung as food for their larvae. Although this beetle is native to Africa, now it has a worldwide (=cosmopolitan) distribution because the species was intentionally introduced to many countries such as Australia, New Caledonia, Hawaii, Puerto Rico and the USA, as a biological control to decrease the dung accumulation caused by cattle and the proliferation of pest flies.
Following its introduction to the USA (in California apparently in 1978, in Texas in 1979, and in Georgia in 1984), E. intermedius started a rapid range expansion across the south of the USA, up to Florida, and Central America, with an estimated speed of about 50 km or more per year. In 1992, it was first recorded in Mexico (the site Mapimí), then it reached Guatemala in 2002, Nicaragua in 2007 and Costa Rica in 2008; in 2015, the beetle was already recorded from the border of Panama (see Maps below).
Maps. A – Dispersal of Euoniticellus intermedius in Mexico after its introduction in the USA (after de Oca & Halffter, 1998). B – Further dispersal of E. intermedius from southern Mexico across the Isthmus of Panama (after Solis et al., 2015).
The beetle has been particularly successful at colonizing arid zones, where the number of native burrowing dung beetles was rather low. For instance, at some places in Mexico, 96% of the individuals (and a great proportion of biomass) corresponded to two invasive dung beetles: E. intermedius and the Gazelle Scarab – Digitonthophagus gazella (Fabricius, 1787), another widely introduced species of dung beetles (see here for further information about it).
But why has the Intermediate Sandy Dung Beetle been so successful in colonizing Americas? There are two main reasons. First, this species has certain biological properties that help its rapid expansion: (1) it is a highly prolific species that can have two or more broods of offspring per year; (2) it is an eurytopic species that can live in a wide variety of habitats and tolerate a wide range of environmental conditions; and (3) it has a preference for bovine dung, which is both very abundant in cattle-farmed areas and nutritionally rich, but yet poorly/not utilized by native Central American species.
Second, quite favourable ecological conditions for E. intermedius (and for D. gazella) have been created by the human activity in Central America: viz., (1) deforestation leading to the creation of open, sunny and dry habitats (=pastures) to which this African species is well-adapted; (2) increase in cattle breeding resulted in the production of excessive amounts of dung (=food resource for the beetle); and (3) the inability of native dung beetles to properly utilize cattle dung, which actually means that there was no competition with native species for this food resource.
Although the ecological impact of E. intermedius on native dung beetles is poorly understood yet, those from the guild of burrowing (=paracoprid) dung beetles are to be affected for sure. Soon we’ll be able to see if this beetle is able to colonize South America and what its presence in the areas already invaded could do to the native biota.
Here and here you can find further information about E. intermedius.
Further reading:
Oca de, E.M. & Halffter, G. (1998) Invasion of Mexico by two dung beetles previously introduced into the United States.- Studies on Neotropical Fauna and Environment, 33(1): 37-45; http://dx.doi.org/10.1076/snfe.33.1.37.2174
Entomology Manchester 