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 orcha rds of Italy's Emilia-Romagna region. The first trial compared densiti es of 2, 10, and 20 traps per hectare, and the second trial compared 1 0, 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 replicatio ns; trial 2 alternated the tested densities over time to reduce compet ition involving two different trap densities. Doubling the number of t raps in the test plots resulted in a 50% increase in capture rate in t he first trial and 10-20% increase in the second. This difference may be explained by assuming a migration of insects from the plots with fe wer 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 s everely infested orchards.