Global and regional pest insects and their antagonists in orchards: spatial dynamics

Abstract

The spatial dynamics of herbivores gains importance when slowly acting pest-management tools are employed. The temporal pattern of the techniques to be used in an agroecosystem has received some attention, particularly with respect to the preservation of certain natural enemies (e.g. predatory mites) as well as with respect to resistance-management programs. The spatial pattern of the techniques applied in neighbouring plots, however, deserves increased attention especially when slowly acting pest-management techniques are involved. This will be exemplified with Cydia pomonella. Laboratory investigations on the flight capacity and the reproductive behaviour revealed characteristics which are in good accordance with unexpected results in the field. Female codling moths showed on a computer-linked flight device a flight capacity which was at least as high as that of the males. Even mated females were capable of long distance flights and subsequent deposition of a sizeable number of eggs. An insecticide frequently used for codling moth control, azinphosmethyl, at certain sublethal dosages altered codling moth behaviour and accelerated egg deposition within the first 24 h after treatment. The implications of these findings from laboratory studies for strategies on both pest management and resistance management are discussed. The spatial dynamics of natural enemies are directed by a number of different cues. Knowledge of these cues may contribute to a more efficient biological control of pest species in the future. The searching behaviour of parasitic antagonists of leafminers Phyllonorycter spp. is reviewed with particular emphasis on the role of olfactory and vibrational stimuli. On long range, olfactory stimuli can lead the parasitoid to the infested host, as was demonstrated for Pholetesor bicolor in the laboratory using a Y-tube olfactometer. On short range, vibrations emitted by the concealed herbivore play a role in the host location as was demonstrated for Sympiesis sericeicornis using a laser Doppler vibrometer. The vibrational signals detected were specific for a certain activity and development stage of the leafminer and clearly distinguishable from abiotic sources of vibration. The impact of these cues on the success of parasitisation in a variable ecological environment is discussed with particular focus on density-dependent effects.