Studie över naturliga fienders roll vid bekämpning av bladlöss och sköldlöss i äppelodlingar samt odlingsteknikens inverkan på den naturliga regleringen av skadeinsekter

Through this project we intent to provide information on the state of the ecosystem service provided by natural enemies through the regulation of several relevant pests in Swedish apple orchards: The woolly apple aphid (Eriosoma lanigerum), the mussel scale (Lepidosaphes ulmi) and the rosy apple aphid (Diaphis plantaginea). We also intend to assess the impact of different orchard management practices on the presence, abundance and diversity of natural enemies, and, ultimately, on their regulatory effect on the considered pest species ,establishing the knowledge required for the development of strategies aiming at the conservation and increase of this pest regulation function. And finally, based on the findings of the field studies concerning the key natural enemies of the considered pests, a literature review will be undertaken in order to identify compounds that are: effective against aphids and scales and relatively innocuous to their key antagonists in Swedish apple orchards.

Genom detta projekt har vi för avsikt att skapa och samla kunskap kring tillståndet för den ekosystemtjänst som de naturliga fienderna erbjuder genom att reglera flera allvarliga skadeinsekter i svenska äppelodlingar: blodlus (Eriosoma lanigerum), kommasköldlus (Lepidosaphes ulmi) och röd äpplebladlus (Dysaphis plantaginea). Vi kommer även att utvärdera olika odlingsteknikers inverkan på förekomst, antal och diversitet av dessa naturliga fiender, och den reglerande effekt de därigenom besitter mot de nämnda skadeinsekterna. Därmed kommer vi att fastställa vilken kunskap som krävs för utvecklandet av strategier som gynnar de naturliga fienderna vilket på längre sikt gör det möjligt att minska mängden bekämpningsmedelsbehandlingar. Slutligen vill vi använda denna kunskap till att genom en litteraturstudie identifiera alternativa bekämpningsmedel med lägre påverkan på naturliga fiender i de fall en applicering är nödvändig.

De naturliga fiendernas (NF) insektspopulationer och deras naturliga biologiska bekämpning av röd äpplebladlus (RÄBL), blodlus (BL) och kommasköldlus (KSL) undersöktes i svenska äppelodlingar. Den biologiska bekämpningen av RÄBL var mycket hög jämfört med kontrollen där bladlössen isolerats från NF. Den högre bekämpningsnivån i ekologiska odlingar var relaterad till rovstinkflyn som angriper små kolonier. Den naturliga predationen halverade KSLs population men inga skillnader hittades mellan ekologiska och konventionella gårdar. Signifikanta nivåer av BL hittades endast på konventionella gårdar. Pollineringsträd har visats vara en källa till BL angrepp och begränsar den biologiska bekämpningen. Kemiska bekämpningsmedel påverkade rovstinkflyn och skalbaggar negativt men visade ingen effekt på tvestjärtar och parasitoider. Svavel hade ingen effekt på de flesta NF och jordbearbetning påverkade inte tvestjärtar. Närvaron av blommor gynnade viktiga predatorer.

Pest insects and mites have associated complexes of organism that consume them and limit their populations. These organisms are comprised by predators, parasitoids and pathogens and are collectively called natural enemies and the control they exert is known as biological control. Predators and parasitoids (hereafter natural enemies) play a very important role in reducing agricultural pests and the damage they cause. Currently, integrated production is mandatory in EU apple orchards and one of the main objectives of integrated pest management (IPM) is to maximize the effectiveness of natural enemies for pest control. Aphids are among the most relevant pests in apple orchards, and other sapsucking pests, such as the woolly apple aphid and the mussel scale, have increased in the past years in Sweden. Natural enemy insect populations and the regulation they provide of the rosy apple aphid (RAA), the woolly apple aphid (WAA), and the mussel scale, were studied in Swedish apple orchards for three years. In two consecutive seasons, potted apple trees infested with the target pests were deployed in orchards under different management regimes (conventional and organic) and varying in other management practices such as soil management and the use of sulfur as disease control product. The development of the pests and the presence of predators and parasitoids were monitored and noted weekly during the growing season. Simultaneously, predators and parasitoids, along with other insects, were collected from apple tree canopies using an insect aspirator, and the presence of flowers (food resources for some natural enemies) was measured. RAA colonies were consumed rapidly compared to protected controls indicating a relevant role of some predators in the control of this pest. From the beginning of the experiment, predatory bugs, mainly Anthocoris nemorum, were observed consuming small colonies. Earwigs, hoverflies, ladybirds, lacewings and predatory midges were also observed. RAA colony suppression was higher in organic compared to conventional orchards due to a higher frequency of predators present in colonies. The populations of natural enemies collected from the canopy revealed that synthetic pesticides used in conventional orchards affected negatively predatory bugs (Anthocoridae and Miridae) and beetles (ladybirds and soldier beetles). However, management type did not affect Earwigs and parasitoids. Higher populations of predatory bugs contributed significantly to predate small RAA colonies preventing colony growth that results in apple damage. Mussel scale biological control halved the development of its population mainly due to predation. Parasitism accounted for 10% destruction of the scales that survived predation. No difference in biological control was observed between organic and conventional orchards probably due to the lack of effect of pesticides on earwigs, their main predators, and parasitoids. WAA was exclusively present in significant densities in conventional orchards supporting that it could be a pesticide-induced pest in Swedish conditions. Predatory bugs, hoverflies, lacewings and ladybirds were observed feeding from WAA colonies. The parasitoid Aphelinus mali was also recorded. In addition, pollenizer trees within orchards, assessed as a separate experiment during the project, were shown to act as a source of WAA infestation for commercial trees and limit A. mali biocontrol capacity. Sulfur spray and understorey soil tillage, practices common in organic orchards, did not impact the most important natural enemies. Surrounding seminatural habitats and flower presence within orchards correlated positively with some important predators as Anthocoridae. Miridae and Anthocoridae populations and biological control could be increased by reducing or substituting pesticides and Anthocoridae by using flower strips and having insect reservoir habitats around orchards.