Initial investigation of Trichogrammatoidea lutea (Hymenoptera: Trichogrammatidae) as biological control agent of codling moth, Cydia pomonella (Lepidoptera: Tortricidae), in apple and pear orchards, under sterile insect technique (SIT)

[摘要] Codling moth (CM), Cydia pomonella (Linnaeus) (Lepidoptera: Tortricidae), is the major pest ofapples and pears in the South Western Cape, South Africa. Apart from conventional insecticidesprays, area-wide biologically intensive control methods, such as Sterile Insect Technique (SIT) andpheromone mediated mating disruption (MD) are currently in use on two farms in the Elgin valley. Theindigenous parasitoid Trichogrammatoidea lutea Girault (Hymentoptera: Trichogrammatidae) attackseggs of false codling moth (FCM), Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae), aswell as CM and has been found to have considerable parasitism potential on both. Elevated host eggnumbers, as achieved by SIT are thought to support establishment of populations of these naturalenemies in the orchards.For rapid and secure Trichogrammatoidea species identification, the ITS2 sequences ofTrichogrammatoidea lutea and T. cryptophlebiae Nagaraja (an indigenous FCM parasitoid on citrus)were determined and species specific primers were developed.Lifetable studies of T. lutea indicated an optimal temperature for reproduction at around 20 °C.Food was provided by the application of honey-solution soaked cotton wool, behind fine netting. Theeffect of food provision by this method was found to be dependent on temperature. The acceptance ofCM eggs from sterilized vs. fertile parents and of radiation-sterilized eggs vs. fertile ones wasassessed in choice trials. While no difference was observed between radiated and fertile eggs, sterileeggs from irradiated parents were significantly less attractive than eggs from fertile parents.In several field studies the dispersal capacity and population sustainability of released T. luteawere investigated. Trials took place in apple and pear orchards in the Elgin valley that formed part ofan area-wide sterile CM SIT program. Most of the wasp releases were carried out within blocks of upto 1 ha. A square grid of up to 36 monitoring trees per block allowed spatial distribution analysis.Following single central point releases, parasitism of sentinel eggs was recorded until the end of allexperiments, the longest of which lasted 37 weeks. T. lutea females were found to disperse up to 73m, within one week.Studies concerning toxicity of four commonly used insecticides and one fungicide to immature andadult T. lutea indicated no to low susceptibility of wasps at egg- to first-instar-stage within host eggs.Contact toxicity of the tested materials to adults differed significantly, depending on the compound. Allfive pesticides caused significantly higher mortality among adults relative to the control. The overall aim of above studies was to determine the potential of T. lutea for broad-scale releasesagainst CM, within a broader integrated pest management program in apple and pear orchards in theWestern Cape.

[发布机构] Stellenbosch University