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

The spatial dynamics of herbivores gains importance when slowly acting pest -management tools are employed. The temporal pattern of the techniques to b e used in an agroecosystem has received some attention, particularly with r espect to the preservation of certain natural enemies (e.g. predatory mites ) as well as with respect to resistance-management programs. The spatial pa ttern of the techniques applied in neighbouring plots, however, deserves in creased attention especially when slowly acting pest-management techniques are involved. This will be exemplified with Cydia pomonella. Laboratory inv estigations on the flight capacity and the reproductive behaviour revealed characteristics which are in good accordance with unexpected results in the field. Female codiing moths showed on a computer-linked flight device a fl ight capacity which was at least as high as that of the males. Even mated f emales were capable of long distance flights and subsequent deposition of a sizeable number of eggs. An insecticide frequently used for codling moth c ontrol, azinphosmethyl, at certain sublethal dosages altered codling moth b ehaviour and accelerated egg deposition within the first 24 h after treatme nt. The implications of these findings from laboratory studies for strategi es on both pest management and resistance management are discussed. The spatial dynamics of natural enemies are directed by a number of differe nt cues. Knowledge of these cues may contribute to a more efficient biologi cal control of pest species in the future. The searching behaviour of paras itic antagonists of leafminers Phyllonorycter spp. is reviewed with particu lar emphasis on the role of olfactory and vibrational stimuli. On long rang e, olfactory stimuli can lead the parasitoid to the infested host, as was d emonstrated for Pholetesor bicolor in the laboratory using a Y-tube olfacto meter. 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 spe cific for a certain activity and development stage of the leafminer and cle arly 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. (C) 1999 Elsevier Science B.V. All rights reserved.