| Abstrakt: |
The population dynamics of the Colorado potato beetle (CPB), Leptinotarsa decemlineata(Say) and its parasitoid Myiopharus doryphorae(Riley) were studied over a 3-year period in two potato fields in Massachusetts. Densities of Colorado potato beetle larvae increased rapidly to maxima of 182, 109, and 102 larvae/m2in 1989, 1990, and 1991, respectively. Host and parasitoid recruitment to the CPB prepupal and the parasitoid larval populations was measured using metal screen cages buried in the ground surrounding potato plants within rows for the first generation and between rows for the second generation. Total CPB larvae recruited to the prepupal stage per square meter were 178.8, 79.5, and 20.7 in the first generation in 1989, 1990, and 1991, respectively. Parasitoid recruitment for the first generation for the same years were 3.8, 27.3, and 7.1 per square meter, respectively, which represented 2.1, 34.3, and 34.4% of CPB recruitment. Total CPB larvae recruited per square meter in the second generation were 4.8 and 23.7 in 1989 and 1991, respectively. Parasitoid recruitment per square meter for the second generation for the same years were 1.5 and 11.3, which represented 31.5 and 47.3% CPB larval mortality from parasitism. Percentage parasitism of larvae collected from foliage for the first generation averaged 3, 10.5, and 1.6% for 1989, 1990, and 1991. In the second generation, percentages parasitism of larvae collected from foliage were 24.5 and 15.7% for 1989 and 1991, respectively. Over the 3-year period, percentage parasitism in foliage samples showed an erratic pattern. Estimates of mortality of CPB larvae derived from recruitment data were consistently in the 30-50% range, even when CPB recruitment was as great as 80 prepupae per square meter per generation, indicating that Myiopharusspp. can cause high levels of mortality to CPB larvae at higher host densities than has been reported in most previous field studies. |
