Detectability of insects in Malaise traps : assessing insect detectability in Malaise traps through High-Resolution Sampling, and development of a novel marking technique

Sammanfattning

Malaise traps are extensively used in insect surveys and studies, yet the detectability of insects in relation to the traps remain unknown. Detectability is the odds that a taxon ends up in a trap, given that the taxon is present in the area around the trap. The detectability of a taxon depends on three main factors – Population size of the taxa, its activity, and its movement patterns. In this study, I aimed to find how weather influence the activity and thus detectability of insects in Malaise traps, and to develop a marking technique for surveying insect movement patterns around the traps. To achieve my aim of developing a novel marking technique, I tested the effect of fluorescent dusts on survival and flight ability of insects, concluding that the dusts showed no overall negative effects. I then developed a passive marking device of insects in Malaise traps, using the fluorescent dusts as marking mediums. I re-released marked individuals in a forest habitat, inside a network of Malaise traps, and emptied the traps each day. The recapture rates of marked individuals were 4.5% and the technique deemed an effective method for passively marking insects. Furthermore, to understand how weather influences activity and subsequent detectability, I conducted High-Resolution Sampling. I emptied 24 Malaise traps every second hour for five days, recording temperature, cloud cover, wind speed and relative humidity at each sampling event. This data was used to investigate how these variables affect insect activity, and in what directions. Increased temperature increased abundances of insects. Increased wind speed and cloud cover lowered abundances. Relative humidity had no effect on abundances. Furthermore, high wind speeds, and to some extent temperatures, subset the sampled community by favouring insects with smaller wing area than expected by the normal wing-to-body ratio. However, the effect of each environmental factor was small. In conclusion, this study shows that Malaise trap samples are robust against fluctuations in weather, and that the novel marking technique presented is an effective method for marking minute insects.