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.

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.

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.