Establishment and spread of Vespula germanica (F.) (Hymenoptera: Vespidae) in New South Wales and the influence of rainfall on its abundance.

Establishment of European wasp, Vespula germanica, in N.S.W. was confirmed in 1978 when 17 nests were destroyed in the Sydney Metropolitan Area (SMA). The number of nests recorded in subsequent years remained low (< 18) until 1982–83, when 74 nests were found. During 1983–84 and 1984–85, the number of nests continued to increase, approximately doubling each year. High nest numbers were recorded throughout the State for the remainder of the monitoring period and peaked at 802 in 1987–88. The area of the SMA infested by V. germanica increased sigmoidally. After increasing rapidly during 1983–84 and 1984–85, the area infested stabilised at approximately 1,400 km2. Nest abundance in the SMA was correlated with annual rainfall (r = 0.776; p < 0.01). It is possible that a shortage of available fresh water is an important factor limiting the spread of V. germanica in the SMA.