Determining the quality of mass reared male codling moth, Cydia pomonella (Lepidoptera: Tortricidae), by assessing flight performance under laboratory, semi-field and field conditions.

Visser, Andri (2016-03)

Thesis (MScConsEcol)--Stellenbosch University, 2016.

Thesis

ENGLISH ABSTRACT: The codling moth, Cydia pomonella (Linnaeus) (Lepidoptera: Tortricidae), is the insect pest that poses the greatest threat to the South African pome fruit industry. Traditionally, insecticides have been used to control this pest, but recently these chemicals have failed to adequately suppress codling moth due to the build-up of resistance in populations. Along with the added pressure from export markets to reduce insecticide residues, the need for feasible control alternatives has never been greater. The Sterile Insect Technique (SIT) is an environmentally friendly control method that has had great success with the control of a number of different insect pests, including codling moth. The technique involves the mass production and release of sterile insects with the goal of over-flooding the natural population, but it is also crucial that the mass reared insects can successfully compete for mating opportunities. However, no comprehensive quality control assessment method currently exists for mass reared codling moth. This study aimed to identify and develop laboratory, semi-field and field methods that can be used to assess the quality of mass reared codling moth. This would be accomplished by developing flight performance assessments that could be used to distinguish between mass reared moths of high and low quality. The experiments conducted for each assessment method compared the flight performance of moths subjected to different treatments of radiation dose, ageing and handling during transport. For the laboratory quality control assessment, a matrix of nine flight cylinders with combinations of three heights (2.5, 15 and 26.5 cm) and three diameters (10, 14 and 16 cm) was developed which compared the escape rate from these cylinders of moths subjected to different treatments. The semi-field assessment (conducted in a horticultural tunnel) measured the arrival time of the moths subjected to different treatments at a trap 12 m from the point of release. Field release/recapture assessments were conducted at two apple orchards in Elgin (one covered with netting and one uncovered), as well as an uncovered pear orchard in Stellenbosch. The flight performance of mass reared moths was determined by evaluating their dispersal rate from a central point of release with a trapping grid of eight pheromone baited delta traps. The efficacy of the three assessment methods was also evaluated for mass reared false codling moth, Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae), in separate experiments. Results indicated that increasing radiation dose had a detrimental effect on moth quality, but no effect could be observed for the age treatments. The effect of bran handling on moth quality could be observed in the field only, suggesting that it is dependent on the time period the moths are transported in the bran. The flight cylinder method was able to accurately indicate of the quality of moths as it relates to flight performance, but that the field assessments were the best indication the overall competitiveness in the field. This was true for both codling moth and false codling moth. The semi-field assessment method was not successful at distinguishing between moths of different quality; the development of an effective semi-field quality test is therefore still on-going.

AFRIKAANSE OPSOMMING: Die kodlingmot, Cydia pomonella (Linaeus) (Lepidoptera: Tortricidae), is die insekpes wat die grootste bedreiging inhou vir die Suid-Afrikaanse kernvrugbedryf. Dié pes is tradisioneel met behulp van insekdoders beheer, maar die toename in weerstandbiedendheid van die kodlingmotpopulasies het veroorsaak dat die chemikalieë hul doeltreffendheid verloor. Tesame met die druk van die uitvoermark om die residue van landbouchemikalieë op produkte te verminder beteken dit dat die behoefte aan n volhoubare beheer metode nog nooit groter was nie. Die Steriele Insek Tegniek (SIT) is ‘n omgewingsvriendelike beheer strategie wat in die verlede suksesvol geïmplementeer is teen ‘n verskeidenheid van insekpeste, onder andere ook kodlingmot. Die tegniek behels die massaproduksie en –vrylating van steriele insekte met die doel om die wilde populasie se getalle te oortref, maar dit is van kardinale belang dat die steriele motte ook suksesvol kan kompeteer vir paringsgeleenthede. Ten spyte hiervan bestaan daar tans geen omvattende kwaliteitsbeheertoetse vir die kodlingmot nie. Dit was die doel van die studie om verskillende kwaliteitsbeheertoetse te ontwikkel vir gebruik in die laboratorium, vir semi-veld omstandighede asook vir gebruik in die boord self. Hierdie doelwit sou bereik word deur toetse te ontwikkel wat die kwaliteit van die motte bepaal op grond van hul vlugvermoë. Die eksperimente het die vlugvermoë van motte vergelyk wat aan verskillende behandelings van bestraling, veroudering en hantering tydens vervoer blootgestel is. Vir die laboartorium-kwaliteitstoets is ‘n vlugsilinder matriks saamgestel wat bestaan het uit nege silinders met kombinasies van drie hoogtes (2.5, 15 and 26.5 cm) en drie breedtes (10, 14 and 16 cm). Die semi-veld assesserings (wat plaasgevind het in ‘n hortologiese tonnel) het die aankomstyd van die verskeie behandelings by ‘n lokval wat 12 m vanaf die vrylatingspunt geplaas is, bepaal. Die vrylaat/terugvang metode is toegepas in ‘n bedekte en ‘n onbedekte appelboord in die Elgin-omgewing, asook in ‘n onbedekte peerboord in Stellenbosch. Die vlugvermoë van die motte is bepaal deur hul verspreidingstempo in ‘n lokvalrooster met agt feromoon-bevattende lokavalle te meet. Die effektiwiteit van die assesseringsmetodes vir die vals kodlingmot (Thaumatotibia leucotreta) is ook bepaal in aparte eksperimente. Die resultate het aangedui dat bestraling mot kwaliteit nadelig beïnvloed, maar dat ouderdom geen effek op die vliegvermoë van motte gehad het nie. Daar kon slegs in die boord ‘n nadelige invloed opgemerk word wanneer motte in hawer vervoer is (en nie in die laboratorium toetse ook nie), wat daarop dui dat die mate van kwaliteit degradasie afhanklik is van die tyd en afstand wat motte in die hawer vervoer word. Die vlugsilindertoets kon die kwaliteit van die motte akkuraat bepaal deur dit te meet aan vlugvermoë, maar die kwaliteitstoetse in die boord het die beste aanduiding gelewer van die algehele kompeteringsvermoë van die massaproduksie-motte. Die semi-veld assesseringsmetode kon nie onderskeid tref tussen hoë- en lae kwaliteit motte nie; dus is die ontwikkeling van ‘n effektiewe semi-veld metode nog nie voltooi nie.

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