Definitions

Irrupt, as in irruptions (insect)
ir·rupt (-rpt)
intr.v. ir·rupt·ed, ir·rupt·ing, ir·rupts
1. To break or burst in.
2. Ecology To increase rapidly and irregularly in number: In the absence of predators, the island's rodent population irrupted¹

labile
Pronunciation: 'lA-"bIl, -b&l
Function: adjective

readily or frequently changing: as a

readily orcontinually undergoing chemical, physical, or biological change or breakdown labile antigen> b : characterized by wide fluctuations (as in blood pressure or glucosetolerance) <labile hypertension> <labile diabetes> c : emotionally unstable —la·bil·i·ty /lA-'bil-&t-E/ noun plural -ties²

Footnotes

1. The American Heritage® Dictionary of the English Language, definition available at http://www.thefreedictionary.com/Irruption.

2. Merriam-Webster's Medical Dictionary, definition available at http://dictionary.reference.com/browse/labile?db=luna.