COMPARISON OF DIFFERENT TRAPPING METHODS IN AGROMYZIDAE (DIPTERA)

Trapping techniques are frequently used to monitor pest species. These trapping techniques have to provide reasonably precise estimates of d ensities and sex ratios of monitored species in order to apply appropr iate insect pest control measures most efficiently. A broad range of t rapping methods are applied to gather this basic ecological informatio n. However, few studies question the reliability of trapping methods t o obtain accurate data. Here, we investigate the usefulness of traps f or the assessment of basic life-history data in Agromyzidae. In this s tudy, Malaise traps and coloured water traps are compared. Significant deviations of a 1 male:1 female sex ratio occurred both in Malaise an d colour traps. The bias of these deviations of the sex ratio altered according to the trapping method. In the Malaise traps most significan t deviations were female biased. All significant deviations observed i n the colour traps were male biased. The overall sex ratio of all capt ured individuals was in every Malaise trap in favour of the females an d in every colour trap in favour of the males. Different trapping meth ods also revealed intraspecific differences in phenology patterns. Agr omyzid flies were trapped earlier in colour traps compared to Malaise traps. Possible explanations for the observed intraspecific difference s in sex ratio and phenology pattern between traps are discussed. This study points out that a thorough analysis of the response of a target species to a certain trapping method is needed in order to ascertain the reliability of the collected data. The importance and consequences of these results for monitoring agromyzid pest species are emphasized .