Lene Sigsgaard

Shallot Aphids, Myzus ascalonicus, in Strawberry: Biocontrol Potential of Three Predators and Three Parasitoids

Abstract The parasitization capacity of 3 parasitoids and the predation capacity of 3 predators towards the shallot aphid, Myzus ascalonicus Doncaster (Homoptera: Aphididae), on strawberry, Fragaria x ananassa Duchesne (Rosales: Rosaceae) cv. Honeoye, were examined in laboratory experiments. In Petri dish assays, both Aphidius colemani Viereck (Hymenoptera: Aphidiidae) and A. ervi Haliday readily stung shallot aphids, with no significant difference in stinging frequency between the two species. A. ervi induced a significantly higher mortality (79.0 ± 7.2%) in terms of stung aphids compared with A. colemani (55.3 ± 4.1%); however, only a minor fraction (2.7 ± 1.8% and 7.1 ± 3.1%, respectively) of the killed aphids resulted in formation of mummies, presumably due to a physiological response to parasitism. The low percentage of mummification precludes the use of either Aphidius species in anything but inundative biocontrol. In similar set-ups, Aphelinus abdominalis (Dalman) (Hymenoptera: Aphelinidae) killed almost half (49.6 ± 5.3%) of the exposed aphids through host feeding. In addition, 23.2 ± 7.3% of non-host-fed aphids developed into mummified aphids, and 38.1 ± 13.2% of non-host-fed aphids died from other parasitoid-induced causes. However, the host feeding rate was reduced to only 1.2 ± 0.8%, and no significant parasitization mortality was observed on strawberry plants, suggesting that host plants interfered with A. abdominalis activity. This parasitoid does not, therefore, seem to be suited to either inoculative or inundative biocontrol of shallot aphids in strawberry. The three predators studied were the green lacewing, Chrysoperla carnea Steph. (Neuroptera: Chrysopidae), the two-spotted lady beetle, Adalia bipunctata L. (Coleoptera: Coccinellidae), and the gall midge Aphidoletes aphidimyza (Rondani) (Diptera: Cecidomyiidae). Third instars of all 3 predators readily preyed upon the shallot aphid in Petri dish set-ups with significant differences in daily predation (34.62 ± 3.45, 25.25 ± 3.18, and 13.34 ± 1.45, respectively). Further studies on A. bipunctata revealed that the larvae maintained their daily predation capacity (32.0 ± 6.3) on strawberry plants. About 60% of already ovipositing A. bipunctata refrained from laying any eggs on the first day after transfer to set-ups with combinations of shallot or peach-potato aphids, Myzus persicae (Sulzer) (Homoptera: Aphididae), and strawberry or sweet pepper leaves. The aphid species and the plant species did not, however, have a significant influence on the number of females laying eggs, the average number of eggs laid during the first day being 6.37±1.28 per female. Adult lady beetles had a significant preference for odor from controls without plants over odors from uninfested strawberry or pepper plants, but they showed no preference for either of the plant species, whether infested with aphids or not. The predation capacity of A. bipunctata on shallot aphids holds promise for its use in inundative biocontrol, and the results on egg laying cues suggests that inoculative biocontrol may be possible, although further studies will be needed for a complete evaluation.

Semiochemical-based pest insect management in strawberry and raspberry

Introduction: For many insect species, pheromones and host plant volatiles are of major importance in mate finding and host plant location. Therefore, there is potential for using these interactions to develop new strategies and effective control measures. The strawberry blossom weevil (Anthonomus rubi), the European tarnished plant bug (Lygus rugulipennis) and the raspberry beetle (Byturus tomentosus) cause large losses (10->80%) in both conventional and organic strawberry and raspberry production. We investigated whether the natural semiochemical mechanisms of these key pests can be exploited to develop effective traps for their management through mass trapping. nMethods: Attractive traps and lures with host plant volatiles and pheromones were developed and combined into a “multitrap” for management of these pests simultaneously. These traps were deployed within and around the perimeters of the soft berry fields. Insect catches were evaluated according to species, habitat and environmental variables. Plant damage was also assessed. n nResults/Conclusion: For both crops it was possible to combine lures so that different targeted insect species were caught in the same trap simultaneously, but optimal insect traps in strawberry were not the same as in raspberry. Perimeter traps and multiple traps placed inside the plantations showed the potential to reduce pest numbers and subsequent fruit damage. In addition, bycatch of non-targeted invertebrate species were low. Thus, it is possible to develop new plant protection strategies by using these techniques. In this paper we will discuss the benefits and difficulties in using these techniques as part of integrated or organic pest management.