Changes in dominance of dipteran families on Coral Sea cays over ten years during a period of substantial vegetation change

The habitat on the Coringa-Herald group of coral cays within the northern Coral Sea underwent profound change after about 2000 because of extensive dieback of the dominant forest trees. This work summarises surveys on these cays in 1995, 1996, 1997 and 2007, in order to understand the effect on the native insect fauna of the introduced biological control agent, the non-specific predatory ladybird beetle Cryptolaemus montrouzieri (Coleoptera: Coccinellidae), that was liberated to control scale insects (Hemiptera: Coccidae) whose infestation was responsible for the dieback of the forest trees. This paper documents the families of Diptera (flies) collected on the surveys and it records changes in presence and abundance of Chloropidae, Phoridae, Sarcophagidae, Canacidae, Lonchaeidae and Chironomidae sampled in pitfall traps and yellow pans. Despite some differences in collecting methods and seasons between surveys, there is evidence of substantial changes in the presence and relative abundance of these families. The decline of several families on Coringa Cay and on North East Herald Cay between 1995/96 and 2007 could be the result of a trophic cascade of species loss following tree dieback. One of the most conspicuous changes was that Chloropidae increased on North East Herald Cay between 1997 and 2007 following increases in populations of scale insects, but chloropids are not thought to have had a direct role in the control of scale insects.