title used in an account of west-coast marine invertebrates entitled A Snail's Odyssey
  Predators & defenses
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  In this section insects as predators are considered, while studies on FISHES, LIMPETS, WHELKS, and SEA STARS are found in other sections.
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Research study 1

map of collection sites used in study of insect predation on barnaclesIt may seem unusual, but certain species of insects are capable of attacking and eating a barnacle.  Many species of dipterans lay eggs in the intertidal area where their larvae and pupae are exposed to periodic immersion by the tides.  However, fly species that prey on barnacles do things differently.  An example is Oedoparena, which lays its eggs on the scutal plates of barnacles.  On hatching, the larvae burrow into the host barnacle’s mantle cavity.  Usually, only 1-2 larvae inhabit any given barnacle.  Once inside, a larva preferentially eats yolky ovarian tissue and then shifts to other tissues.  When all tissues are consumed, the larva emerges during a low-tide period to find another prey barnacle.  The larva attaches to the second barnacle with specialised hooks and enters when its prey opens on the incoming tide.  Pupation occurs within the empty test of the larva's last meal, and the larva overwinters as a pupa and emerges in spring. 

Studies in northern Washington state show that barnacles Balanus glandula are variably infested with larvae,with higher levels occurring at quiet-water sites within Puget Sound than at more wave-exposed stations along the Strait of Juan de Fuca (see graphs lower Right). Note that peak larval abundances occur in late spring and early summer. 

Laboratory experiments at Hopkins Marine Station, California in which conditions of summer tidal exposure are simulated, show that Oedoparena larvae can tolerate temperatures as high as 38oC for 3-h periods, although temperatures higher than this graph showing percentage infestion of barnacles Balanus glandula with larvae of dipterans Oedoparena spp. in northern Washingtonare lethall. The larvae survive immersion in seawater (13oC) for periods of up to 4d.  Overall, the authors report infestation frequencies as high as 22% for B. glandula and 35% for C. dalli, but add that mortality is likely much higher than this because the larvae serially kill multiple barnacles.  Harley & Lopez 2003 Invert Biol 122: 61.

NOTE  the authors explain that while 2 species live on the west coast, O. glauca and O. nigrifrons, they cannot be differentiated as larvae

NOTE  the barnacle Chthamalus dalli is also preyed on by Oedoparena, with up to 70% being infested in some areas of Puget Sound