OPTIMAL TRAP DENSITY IN COSSUS-COSSUS (LEPIDOPTERA, COSSIDAE) MASS-TRAPPING

To determine optimum trap density for mass-trapping of Cossus cossus (L.) males, two trials were conducted over 5 yr in apple and pear orchards of Italy's Emilia-Romagna region. The first trial compared densities of 2, 10, and 20 traps per hectare, and the second trial compared 10, 20, and 40 traps per hectare. Trial 1, based on the assumption that the insect was fairly stationary, used 1/2-ha plots in two replications; trial 2 alternated the tested densities over time to reduce competition involving two different trap densities. Doubling the number of traps in the test plots resulted in a 50% increase in capture rate in the first trial and 10-20% increase in the second. This difference may be explained by assuming a migration of insects from the plots with fewer traps to those with more traps. Even at a density of 10 traps per hectare the number of captured males diminished considerably over time. Increases in captures at higher trap densities were moderate. Thus, a density greater than 10 traps per hectare is unnecessary except in severely infested orchards.