During 1989-2006 the number of live aphid, mummies, aphid specialist predators and their parasitoids in cereal fields in Serbia were recorded. S. avenae and M. dirhodum were the most common, both on wheat and rye crops. Maximum numbers of cereal aphids were detected between the end of May and the middle of June. A low percentage of mummified aphids was recorded during May and June, but increased rapidly at the beginning of July, when aphids left the wheat crop. Here, we record over 60 species of cereal aphid natural enemies, including primary and secondary parasitoids, aphid specific predators and a wide spectrum of their parasitoids in Serbian cereal crop systems. Aphidius uzbekistanicus Luzhetzki, Aphidius rhopalosiphi De Stefani, Aphidius ervi Haliday and Praon gallicum Starý were the most abundant species of primary parasitoids. Of the secondary parasitoids, six species were dominant with Asaphes suspensus (Nees) and Dendrocerus carpenteri (Curtis) generally the most often recorded. Coccinella septempunctata L. was the most abundant coccinellid and syrphid flies were represented by 11 species, two of which, Sphaerophoria scripta (L.) and Episyrphus balteatus (DeGeer), were the most common.
A tobacco field in Greece was sampled during the 2001 and 2002 growing seasons to assess the seasonal trends in densities and spatial distributions of the aphid Myzus persicae (Sulzer) and its predatory mirid Macrolophus costalis (Fieber). On repeated occasions between June (just after the transplantation) and September (just before harvest), 20 tobacco leaves (10 from the upper and 10 from the lower plant part) were taken from randomly chosen plants. These leaves were sampled for aphids and mirids. In both years, the highest aphid densities were recorded during July and August, while aphid numbers were low in September. In contrast, the majority of M. costalis individuals were found during September when aphid numbers were low. Significantly more M. persicae individuals were found in the upper part of the plants, whereas significantly more M. costalis individuals were found in the lower part of the plants. As indicated by Taylor's Power Law estimates, both species were aggregated in their spatial distributions among sampling units (leaves). Wilson and Room's model, based on the Taylor's estimates, was used to calculate the mean number of aphids and mirids, from the proportion of sampling units (leaves) that had > 0 individuals of each species. This model provided a satisfactory fit of the data for both the aphid and the mirid. In addition, Wilson and Room's model was successfully used to predict the mean number of aphids and mirids in a series of samples that were carried out in the same area between June and September 2003 for model validation. Finally, equations are given for the calculation of precision in estimating the mean number of aphids or mirids per sampling unit, and the required sample size for a given level of precision.
The behavioural responses of two species of stored-product beetles, Sitophilus oryzae (L.) and Tribolium confusum Jacquelin du Val, to certain stimuli were studied in laboratory choice tests. The results of these experiments indicated that, with one species present, S. oryzae and T. confusum adults were equally attracted to traps baited with the aggregation pheromone of that species and to traps baited with both pheromones. In contrast, when both species were present, neither S. oryzae nor T. confusum showed specific behavioural trend towards a stimulus. Traps baited with 1 g of a mixture of plant extracts were significantly more attractive for both species than unbaited traps, but this response was highly influenced by the number of individuals of each species released. Traps baited with filter papers that were previously contaminated by live adults of both species were particularly attractive for S. oryzae, but not for T. confusum. Traps that contained 10 seeds damaged by S. oryzae were significantly more attractive than traps containing an oil lure or control traps for S. oryzae, but not for T. confusum. The addition of oil to the seeds did not affect the attractiveness of the trap for S. oryzae. Traps that contained 20 live S. oryzae adults were significantly more attractive than traps containing 20 dead S. oryzae adults or control traps. No significant differences were noted between traps containing 20 dead S. oryzae adults and control traps. The presence of S. oryzae adults in traps did not affect the response of T. confusum.