Abstract
Aphid species feeding on lettuce occupy distinct feeding sites: the lettuce aphid Nasonovia ribisnigri prefers to feed on heart leaves, whereas the potato aphid Macrosiphum euphorbiae feeds only on outer leaves. The aphid parasitoid Aphelinus abdominalis, known to be able to regulate M. euphorbiae on many crops, has recently been indicated as a promising biocontrol candidate also for use against N. ribisnigri, a major pest of lettuce. This study therefore examined A. abdominalis parasitization preference between N. ribisnigri and M. euphorbiae and its ability to parasitize aphids feeding on different parts of lettuce plants. In addition, life history traits of A. abdominalis on these aphid species were investigated. In no-choice laboratory experiments on leaf discs and 24 h exposure, A. abdominalis successfully parasitized 54% and 60% of the offered N. ribisnigri and M. euphorbiae, respectively, with no significant difference. In the corresponding choice experiment, however, A. abdominalis had a tendency for a significantly higher preference for M. euphorbiae (38%) compared to N. ribisnigri (30%). Growth chamber experiments on whole plants demonstrated that A. abdominalis was able to parasitize aphids, regardless of their feeding locations on lettuce plants. However, aphid feeding behavior had a significant effect on the parasitization rate. A. abdominalis parasitized significantly higher percentages of M. euphorbiae or N. ribisnigri when aphids were exposed separately to parasitoids on whole lettuce plants as compared with N. ribisnigri exposed only on heart leaf. A significant preference of A. abdominalis for M. euphorbiae compared to N. ribisnigri was also observed in the growth chamber choice experiment. A high percentage of adult emergence (> 84%) and female-biased sex ratio (> 83%) were found irrespective of the aphid species.
Highlights
Infestation by aphids is a serious problem in the production of lettuce, Lactuca sativa L. (Asterales: Asteraceae), both in glasshouses and under field conditions [1]
This study showed that A. abdominalis has the ability to successfully parasitize two aphid species N. ribisnigri and M. euphorbiae when they were offered simultaneously or separately to a parasitoid on the same leaf discs
In the choice situation, there was a tendency for A. abdominalis successfully parasitizing more M. euphorbiae than N. ribisnigri, with parasitization of 38 ± 3.32% and 30 ± 2.50% respectively (Fig 1B)
Summary
Infestation by aphids is a serious problem in the production of lettuce, Lactuca sativa L. (Asterales: Asteraceae), both in glasshouses and under field conditions [1]. The other two species M. persicae and M. euphorbiae are usually considered of lesser economic importance as they only feed on outer lettuce leaves [6] and occur less frequently during the growing season [4, 5, 8]. Control strategies for N. ribisnigri populations on lettuce rely largely on the use of insecticides [9, 10, 11]. Demand for alternative methods to control N. ribisnigri has been stimulated due to the increased risk of insecticide resistance in aphid populations [12, 13], and because of concerns related to the environment [14] and human health [15]. A further potential method for N. ribisnigri biocontrol is the use of parasitoids [22]
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