Field biology and identification of fruit flies in the Western Cape Province

Hobololo, Vuyisile Lanele (2004-12)

Thesis (MSc)--University of Stellenbosch, 2004.

Thesis

ENGLISH ABSTRACT: Two fruit fly species, Ceratitis capitata (Wiedemann) and C. rosa (Karsch) (Diptera: Tephritidae) are known to attack deciduous fruit in the Western Cape Province of South Africa. The relative abundance of these two pests was studied in different kinds of fruit throughout the year. To facilitate field monitoring, using the immature stages, morphological differences between larval instars of C. capitata and C. rosa were investigated. Morphological characters of the larvae, such as the spiracles (anterior and posterior), mouth hooks and oral ridges were used. Many of these characters are only suitable to distinguish between the second and third instar larvae as these structures are not yet developed in the first instar larvae. Anterior spiracles were examined in terms of the number of tubules (papillae) and size or shape of the felt chambers. The number of papillae in both species was similar in the second and third instar larvae, but differed between the larvae of the two species (8-10 for C. capitata and 10-13 for C. rosa). In both species the felt chambers of the second instar larvae were narrow and elongate whilst those of the third instar larvae were broad and short. The major difference between the mouthhooks of the two tephritids was the presence of a sub-apical tooth in the third instar larva of C. rosa, being absent in the third instar of C. capitata. For the morphometric study, both laboratory-reared and field-collected specimens were examined. Measurements of the body dimensions (length and width) and various parts of the cephalopharyngeal skeleton (CPS) (mandible base, mandible length and distance between the tip and notch) were recorded in all three instars of both C. capitata and C. rosa. The data were analysed using finite mixture analysis (FMA-N1) and Levene's test was used to test for homogeneity of variances. The results of these analyses were used to estimate the frequency distributions of the larval measurements. In some cases overlaps in distributions were evident and were resolved using the same program, finite mixture analysis (FMA-N1), based on the probability of the overlapping measurements belonging to the designated instar (i.e. the one with highest probability). Determination of growth ratios suggested an approximate conformation to Dyar's rule thereby disputing the possibility of any hidden instar. However, in most cases measurements of the field samples did not conform to Dyar's rule. For the larval instars of C. capitata and C. rosa with overlapping morphological features, the morphometric approach as a distinguishing tool was demonstrated. In the field survey, the relative abundance of C. rosa at all experimental sites was very low in both orchards and adjacent vines. This suggested that this pest was either not a threat in these sites (crops) or the monitoring procedures applied, should be revised. Trap catches indicated high levels of infestation by C. capitata on some sites and low infestation levels at others. On the site with the highest population levels, activity peaks in the orchards did not co-incide with those in the adjacent vineyards. This suggested that these vineyards could be alternative hosts for fruit fly after the fruit in the orchards have been harvested. Forced oviposition (in vitro) studies indicated that Colombard (grown in Simonsvlei) was the most suitable host for survival of C. capitata. Other wine grape cultivars such as Chardonnay were also suitable for the total larval development of C. capitata.

AFRIKAANSE OPSOMMING: Twee spesies van die vrugtevlieg, Ceratitis capitata (Wiedemann) en C. rosa (Karsch) (Diptera: Tephritidae), val sagtevrugte in die Wes Kaap Provinsie van Suid- Afrika aan. Die groot hoeveelheid van hierdie twee plae op verskillende soorte vrugte is regdeur die jaar bestudeer. Voordat enige insekplaag gemonitor kan word, is dit belangrik dat die identiteit van die besondere plaag, insluitend sy onvolwasse stadiums, bekend moet wees. In hierdie studie word die morfologiese verskille tussen die larwe stadiums van C. capitata en C. rosa ondersoek. Kenmerke soos die spirakels (voor en agter), mondhake en mondriwwe is gebruik. Baie van hierdie morfologiese kenmerke kan net gebruik word om te onderskei tussen larwes in die tweede en derde stadiums omdat hierdie strukture nog nie in die eerste stadium ontwikkel is nie. Die voorste spirakels is ondersoek in terme van die aantal tubules (papillae) en die grootte en vorm van die vilt kamers. In beide spesies is die aantal papillae dieselfde vir die tweede en derde larwe stadiums, maar daar was en verskil tussen die larwes van die twee spesies (8-10 vir C. capitata en 10-13 vir C. rosa). In altwee spesies was die viIt kamers van die twee stadium larwes sma I en verleng, terwyl dit in die derde stadium larwes breed en kort was. Die hoof verskil tussen die mondhake van die twee vrugtevliee was die aanwesigheid van die subapikale tand in die derde stadium larwe van C. rosa, terwyl dit afwesig is in die derde stadium van C. capitata. Vir die morfometriese studie is voorbeelde van laboratorium geteelde vrugtevliee, asook vilee wat in die veld gevind is, ondersoek. Die liggaamsafmetings (Iengte en breedte) is gemeet asook die skelet (mandibel basis, mandibel lengte en die afstand tussen die punt en die kerf) in al drie stadiums van C. capitata en C. rosa. Die data is ontleed deur middel van eindige mengsel analise (FMA-N1) en Levene se toets is gebruik om vir homogeniteit en variansies te toets. Die resultate van die ontleding is gebruik om die frekwensie verspreiding van die larwale metings te skat. In sommige gevalle was daar oorvleueling en dit is opgelos met die gebruik van dieselfde program FMA-N1 baseer op die moontlikheid dat die metings wat oorvleuel, aan die aangeduide stadium (d.w.s die een met die hoogste waarskynlikheid) behoort. Die vasstelling van groei ratios dui aan dat dit naasteby ooreenstem met Dyar se reel en dus die moontlikheid van 'n versteekte stadium betwis. Maar in die meeste gevalle stem die veldmonsters nie ooreen met Dyar se reel nie. Die feit dat die morfometriese benadering die verrnoe het om larwale monsters met oorvleuelende morfologiese kenmerke, beteken dat dit kwalifiseer as In instrument om tussen die larwe stadiums van C. capitata en C. rosa te onderskei. Baie min C. rosa is in vrugteboorde en in nabygelee wingerde gevind. Dit dui of dat die plaag nie 'n bedreiging vir die vrugte inhou nie, of dat die monitor prosedures hersien moet word. Lokvalle dui aan dat daar 'n hoe vlak van infestasie van C. capitata in sommige gebeide is en In lae vlak in ander. Op die plek met die hoogste bevolking van vrugtevliee het die aktiwiteit in die boorde nie ooreengestem met die aktiwiteit in die nabygelee wingerde nie. Dit dui aan dat hierdie wingerde 'n alternatiewe blyplek bied aan die vrugtevliee nadat die vrugte in die boorde geoes is. Gedwonge oviposisie studies dui aan dat C. capitata die beste kan oorleef in Colombard (gekweek te Simonsvlei). Ander wyndruif kultivars is ook geskik vir die ontwikkeling tot by die laaste larwe stadium van C. capitata.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/49966
This item appears in the following collections: