The use of common elder Sambucus nigra to promote Aphidophagous syrphids in apple orchards.

Elder shrubs (Sambucus nigra L.) were planted in an experimental apple orchard as bordering hedgerow with the objective of rearing syrphids (Diptera: Syrphidae) and consequently enhancing the biological control of the rosy apple aphid Dysaphis plantaginea (Passerini). The inoculative introduction of the specific elder aphid Aphis sambuci L. (Homoptera: Aphididae) in late March 2002 and again in 2003 led to the complete hedgerow turning into an early and productive alternative prey reservoir for indigenous syrphids. The species Scaeva pyrastri (L.), S. selenetica (Meigen), Syrphus ribesii (L.), S. vitripennis Meigen, Epistrophe eligans (Harris), E. nitidicollis (Meigen), Platycheirus scutatus (Meigen), Eupeodes corollae (F.), Meligramma triangulifera (Zetterstedt) and Episyrphus balteatus (De Geer) developed on the elder hedgerow during the spring 2002 taking advantage of the aphid infestation. The season 2003 was characterised by a quite different species abundance pattern as, contrary to the previous year when both monovoltine and polyvoltine species were equally represented, the monovoltine syrphids (Epistrophe spp.) represented the dominant group exploiting the elder aphids. A parallel analysis showed that the faeces of the first adult syrphids observed ovipositing on the elder hedgerow in spring contained digested pollen of mainly apple. Our observations indicate the possibility of establishing a local population of monovoltine syrphids in apple orchards by managing an aphid-infested elder hedgerow, without any additional pollen or nectar producing plants.

Seasonal coincidence between rosy apple aphid fundatrices and their parasitoids: implications for an early biological control of Dysaphis plantaginea.

The potential contribution of the aphid parasitoid Ephedrus persicae Froggatt (Hymenoptera: Braconidae, Aphidiinae) in regulating stem mothers of the rosy apple aphid Dysaphis plantaginea (Passerini) (Homoptera: Aphididae) was investigated in culture conditions using both species' phenological emergence data in spring and host stage suitability trials. In 2003, emergence of E. persicae started on April 1st, i.e., 108.2 degree-days (base: 4.5 degrees C; start date: January 1st) later than its host on March 10th. When less than 3% of parasitoids had emerged on April 12th, more than 97% of D. plantaginea stem mothers had moulted beyond their 1st instar. The latest parasitoids left their diapause mummies in late April as the majority of fundatrices had reached the adult stage. Parasitisation trials demonstrated the suitability for E. persicae of all developmental stages of rosy apple aphid fundatrices, including mature individuals. No offspring were deposited by fundatrices parasitised as Ist-instar nymphs but later instars did produce a progeny whose size was substantially reduced compared with unparasitised individuals, and scaled against their age at the time of parasitisation. Although the temperature accumulation required for emergence in spring is reached later for E. persicae than for its host aphids, thus allowing part of the stem mother population to temporarily escape parasitisation and reach maturity, the marked reduction in fecundity of individuals parasitised even as late-instar nymphs does confer to E. persicae a non-negligible role in potentially regulating D. plantaginea.

Internal labelling of the eggs of the aphidophagous hoverfly Episyrphus balteatus (De Geer) (Diptera: Syrphidae) with a fluorescent dye.

A method was developed to label the egg load of Episyrphus balteatus (De Geer) (Diptera: Syrphidae) by feeding adult females with the fluorescent dye Rhodamine B. In a preliminary experiment aimed at selecting an appropriate dye concentration, gravid females reared in insectary conditions were provided for two successive days with a 50% honey-water solution enriched with Rhodamine B at concentrations of 0.1%, 0.01% and 0.001%. Eggs deposited on aphid-infested broad bean plants by syrphid females fed with Rhodamine B 0.01% showed the most intense marking. The higher dye concentration induced irregular marking among the eggs, presumably due to its repellent taste and consequently lower intake by the flies. A second series of trials focused on the persistence of the marker, prior and after oviposition, at the selected (optimal) dilution. A reduction in the marking degree of eggs was observed when the first egg deposition was delayed for one day after removing the dye from the cage. When marked females were allowed to deposit further batches of eggs the subsequent days, fewer eggs were laid and their fluorescence properties was reduced. Exposure to direct sunlight during 10 hours had no detectable effect on the fluorescence level of marked eggs deposited on a bean plant. The egg-marking technique examined in this study could be useful to determine the crop area accommodating eggs deposited by marked syrphid females migrating from a release point into cultivated fields.

Screening low fire blight susceptible Crataegus species for host suitability to hawthorn leaf-curling aphids (Dysaphis spp.).

The group of hawthorn leaf-curling aphids (Dysaphis spp.) hosted by the common hawthorn Crataegus monogyna Jacq. may play an important role in the biological control of the rosy apple aphid, Dysaphis plantaginea (Passerini), by increasing reproduction opportunities for the indigenous hymenopteran parasitoid Ephedrus persicae Froggatt. Unfortunately, most fruitgrowers hesitate to introduce the common hawthorn in their orchards because they fear fire blight infections which may be transmitted by this highly susceptible hawthron species. This potential hazard led us to investigate the suitability to leaf-curling aphids of alternative Crataegus species. As representative for these closely-related aphids, the species Dysaphis apiifolia petroselini (Börner) was used in the trials. Ten Crataegus species characterized by their very low susceptibility to fire blight were examined from two angles. Firstly, aphid sexuals were introduced in autumn onto the different species to verify whether egg laying could take place. Secondly, the development of fundatrices and gall formation were followed the next spring. Although eggs and mature fundatrices could be obtained on almost all species, no fundatrice-hosting galls were recorded in spring. The possible causes of these negative results with respect to the geographical origin of the particular Crataegus species involved in this work are discussed.