Itching for an Answer: Gall-Forming Biological Control Agent Contains an Itch Mite Species Found at Localities Known for Periodic ‘Bite Outbreaks’

Biological control is an attractive option for controlling invasive plant species that are difficult to manage otherwise. However, the release of a non-native species as a biological control agent carries risks. The most obvious risk relates to impacts on plant species other than the plant species targeted for control. There are, however, also other risks. We report on a potential unintended impact of Dasineura dielsi, a gall-forming biological control agent that was released against Acacia cyclops in South Africa in 2003. We confirmed that the galls formed by D. dielsi on A. cyclops harbor mites in the genus Pyemotes (P. cf. ventricosus) within their gall structures, which are parasites of various insect species, but are also known to cause dermatitis in humans. Sporadic biting incidences have been reported in at least two locations in South Africa. The implications are that manual clearing of A. cyclops may expose humans to itch mites and to risks of bites. Gall-forming insects and fungi are known to create niches for herbivores and other gall-associated fauna. Although every possible food web interaction cannot be predicted, enough evidence exists to require that agent screening to include non-target risks other than those pertaining to non-host plants. Testing only whether agents are compromised by interactions with non-target plant species is not sufficient during agent evaluation. If such associations are known from the native range and therefore can form in the introduced range, then any known risk to health and socio-economic activities should be disclosed. We argue for the general development of objective assessment of such risks compared with the benefits potentially accruing from successful biological control of the target plant.