1. Dynamic models of optimal foraging predict that an animal's decision to accept or reject a patch depends not only on the environment and patch quality, but also on its internal state. Previous experiments have shown that the two-spot ladybird beetle, Adalia bipunctata (L.), is reluctant to lay eggs in a patch of prey contaminated by the oviposition-deterring pheromone produced by conspecific larvae.2. An experiment was conducted to test whether the internal state of an A. bipunctata female affects its oviposition response to oviposition-deterring pheromone. Firstly, the oviposition response to oviposition-deterring pheromone of young and old females was compared. Secondly, the oviposition response to oviposition-deterring pheromone of females previously exposed continuously to oviposition-deterring pheromone was compared with that of females of the same age but with no previous experience of oviposition-deterring pheromone.3. Old females and females with previous experience of oviposition-deterring pheromone were less reluctant to lay eggs in the presence of oviposition-deterring pheromone than young and naive females. These results are consistent with the predictions of optimal foraging theory.
The mirid Macrolophus caliginosus Wagner (Hemiptera: Miridae), and the syrphids, Sphaerophoria rueppellii (Wiedemann), Sphaerophoria scripta (L.), and Episyrphus balteatus (DeGeer) (Diptera: Syrphidae), belong to the aphidophagous guild, feeding on aphids (Hemiptera: Aphididae) in Mediterranean vegetable crops. The direction, symmetry, and intensity of intraguild predation between different instar combinations of syrphids and mirid were studied in an arena without plants. Moreover, predatory interactions between syrphids and mirids on plants were also evaluated. The results obtained in the arena without plants demonstrated mutual intraguild predation, i.e., syrphid eggs were highly susceptible to predation, whereas mirid nymphs and adults were attacked by syrphid larvae. All syrphid species showed the same propensity to predation, which was unaffected by parasitism of syrphid larvae by Diplazon laetatorius (Fabricius) (Hymenoptera: Ichneumonidae). Sphaerophoria scripta eggs were less susceptible to predation than those of the two other syrphid species. The experiment performed on plants showed different results. Predation by syrphid larvae on mirids never exceeded 10%, while 100% of syrphid eggs were preyed upon after 48 h. Intraguild predation rates were not influenced by the presence or absence of aphids on the plants. This study demonstrated that results obtained from studying intraguild predation in arenas that are highly artificial should be interpreted cautiously. Depending on the colonization history of a particular habitat in the field, syrphids should be more vulnerable to predation by mirids than vice versa.
Intraguild predation (IGP) among predatory species can influence many plantarthropod associations. However, the relevance of IGP is poorly understood for truly omnivorous species such as those that can complete development on both animal and plant diets. Here we test the hypothesis that IGP among two omnivorous mirids is more common when extraguild food is either absent or not suitable. Laboratory experiments were performed in experimental cages in order to determine the effect of intraguild prey densities and diet availability on direction and intensity of IGP between Dicyphus tamaninii and Macrolophus caliginosus (Heteroptera: Miridae). Intraguild predation was symmetrical between the two mirid species in the absence of alternative food. Increasing densities of intraguild prey enhanced drastically the incidence of IGP. Intraguild predation was reduced when mirids were in the presence of green or red tomato fruits, but the presence of any other extraguild resources had no impact on IGP level. However, when given before the experiments, all resources with the exception of tomato leaves significantly reduced IGP. A second experiment was performed on live plants to compare the results of the previous trials with that obtained in a more natural setting. No IGP was observed when both mirid species were present on a plant. However, development of the intraguild prey (the more vulnerable stage) was hindered by the presence of the intraguild predator. The potential of such results is discussed from community ecology and biological control perspective.
Abstract. The capacity of the green lacewing Chrysoperla rufilabris (Burmeister) to modify its oviposition strategy in response to extraguild prey availability in an oviposition site was studied. Gravid females were placed in presence and absence of aphids. Fecun dity, fertility, dispersion and hatching synchrony were compared. Results indicate a statistical difference in the hatching synchrony of eggs. However, no statistical differences were observed in the proportion of infertile eggs and in egg dispersion. We suggest that C. rufilabris can alter hatching synchrony of eggs in condition of food scarcity in order to favour intra-clutch egg cannibalism by newly hatched larvae and thus increase its overall reproductive success.
The quality of different species of aphids as food for aphidiphagous ladybird beetles varies greatly. The optimal oviposition theory predicts that a female should lay eggs preferentially in patches of suitable prey and should be reluctant to oviposit in patches of less suitable prey. A no-choice experiment was used to test whether aphids (Homoptera: Aphididae) of different suitability influence the oviposition behaviour of the two-spot ladybird beetle, Adalia bipunctata (L.) (Coleoptera: Coccinellidae). The results indicate that A. bipunctata females are not more reluctant to lay eggs in the presence of moderately suitable compared to highly suitable aphids. However, females laid fewer eggs in the presence of toxic aphids.
Two experiments were done to determine the susceptibility of six wild potato accessions to the aphids Macrosiphum euphorbiae (Thomas) (Hemiptera: Aphididae) and Myzus persicae (Sulzer). Densities of aphid colonies were compared between caged Solanum pinnatisectum Dunal (Solanales: Solanaceae), S. polyadenium Greenmam, S. tarijense Hawkes, S. infundibuliforme Philippi, S. oplocense Hawkes, and S. stoloniferum Schlechted and Bouché, and the commercially cultivated potato plant S. tuberosum L. cv. Désirée. Moreover the susceptibility of S. polyadenium and S. tarijense to the Colorado potato beetle Leptinotarsa decemlineata (Say) (Coleoptera: Chrlysomelidae), the potato flea beetle Epitrix cucumeris (Harris), and the potato leafhopper Empoasca fabae (Harris) (Hemiptera: Cicadellidae) was compared to that of S. tuberosum cv. Désirée in the field. Results indicated that S. polyadenium and S. tarijense were more resistant to M. persicae than S. pinnatisectum and the commercially cultivated S. tuberosum cv. Désirée. Solanum polyadenium was more resistant to aphids than S. tarijense in 2004, but not in 2005. Moreover, S. polyadenium and S. tarijense were more resistant than S. tuberosum cv. Désirée to L. decemlineata, E. cucumeris and E. fabae.
Apple aphid, Aphis spp. (Hemiptera: Aphididae), and predator populations in an apple orchard at the non-bearing stage: The impact of ground cover and cultivar BRUNO Abstract.A two-year field experiment was conducted to determine whether a conservation biological control strategy could be applied to enhance the biological control of green apple aphids, Aphis spp., in a high-density and scab-resistant apple orchard at the non-bearing stage. The natural occurrence of aphid predators and their impact on aphid populations were evaluated in 2005. The impact of predation on aphid densities was evaluated by comparing a predator exclusion treatment with a control. In 2006, the possibility to enhance predator abundance/performance and aphid biological control with a flowering ground cover was tested: trees were grown either with a flowering ground cover of phacelia, Phacelia tanacetifolia Bentham, and buckwheat, Fagopyrum esculentum Moench, or with a conventional ground cover of mixed Poaceae species. In 2006, it was also determined whether aphid densities differ between Liberty and Topaz, 2 scab-resistant cultivars. Results indicate that the predatory arthropod community was dominated by Coccinellidae, Cecidomyiidae, and various spider species. The ladybird community was dominated by the exotic species Harmonia axyridis Pallas, and the abundance of this species was correlated with aphid density. Naturally occurring predators had little impact on aphid abundance, although the proportion of trees with aphid colonies was greater in the predator exclusion treatment on two consecutive dates in 2005. Ground cover types had no impact on aphid densities. The oviposition response of Cecidomyiidae to aphid density was greater in Liberty trees with flowering ground cover than with the conventional ground cover. Conversely, the response of ladybird adults to aphid density was more important in Topaz trees with the conventional ground cover than with the flowering ground cover. Finally, no difference occurred in aphid abundance between Liberty and Topaz trees. Those results are discussed from a biological control and ecological point of view.
Abstract.A laboratory experiment was conducted to determine whether the predation strategy of larvae of the aphidophagous silver fly Leucopis annulipes Zetterstedt (Diptera: Chamaemyiidae) is furtive, as are larvae of the aphidophagous midge Aphidoletes aphidimyza Rondani (Diptera: Cecidomyiidae), or active like aphidophagous ladybird beetle larvae (Coleoptera: Coccinellidae). The impact of L. annulipes larvae on pea aphid, Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae), colony disturbance was evaluated and compared with that of the furtive predator A. aphidimyza and the active-searching ladybird beetle Harmonia axyridis Pallas. Results indicate that aphids showed significantly fewer defensive acts (dropping, walking away, wriggling) in the presence of L. annulipes larvae than of ladybird beetle larvae. Furthermore, the impact of L. annulipes larvae on aphid colony disturbance was similar to that of A. aphidimyza and to a control treatment without predators. These results clearly indicate that L. annulipes larvae use a furtive predation strategy.
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