Diversity and ecology of phytophagous weevils in the deciduous fruit industry, South Africa

Magagula, Mxolisi Meshack (2019-03)

Thesis (MScConsEcol)--Stellenbosch University, 2019.


ENGLISH ABSTRACT: The banded fruit weevil, Phlyctinus callosus, Boheman, 1834 (Coleoptera: Curculionidae), is a serious and economically significant pest of apple orchards and vineyards in the Western Cape Province of South Africa. Adults can be accidentally packed with export fruit causing quarantine problems and is regarded as an international phytosanitary pest. A nine month population survey (during the fruiting season of September 2017 to May 2018) was conducted in three different fruit growing areas, namely; Stellenbosch, Ceres and Grabouw, Western Cape Province, South Africa, to determine the assemblage structure and an identification key was compiled for all weevils found in vineyards and apple orchards during this survey. Fortnightly monitoring using 15 cm cardboard bands (tied around the base of the trunk), has indicated that there were nine weevil species found to occur in apple orchards and vineyards, namely, Eremnus atratus (Sparrmann, 1785), Eremnus chevrolati Oberprieler, 1988, Eremnus occatus Boheman, 1843, Eremnus setifer Boheman, 1843, Naupactus leucoloma Boheman, 1840, Pantomorus cervinus (Boheman, 1840), Phlyctinus callosus Boheman, 1834, Sciobius tottus (Sparrmann, 1785) and Tanyrhynchus carinatus Boheman, 1836. Vineyards recorded the highest diversity with eight species recorded: T. carinatus, P. callosus, E. setifer, E. atratus, E. chevrolati, E. occatus, P. cervinus and N. leucoloma, whereas apple orchards recorded the lowest diversity with only four weevil species found: S. tottus, P. cervinus, E. atratus and P. callosus. E. occatus was collected for the first time in vineyards. All nine species belong to the sub-family Entiminae (root weevils). T. carinatus was found in low abundance and it is the only weevil species with a long rostrum and easier to distinguish from the rest of the weevils collected during the study. The rest of the weevils differ only slightly in morphology, especially the Eremnus. Based on collected species during the survey, an illustrated morphological key was produced with species identification information. DNA barcoding was supplied to provide a complementary diagnosis tool. Seasonal monitoring was undertaken to establish population peaks during the fruiting season, in relation to P. callosus, which was regarded as a key pest in apple orchards and vineyards. Furthermore, damage assessments were conducted by assessing fruit clusters or bunches and recording the percentage damage per block, first in early December (pre-thinning assessment) and later in early April (pre-harvest assessments). Weevils emerged in midOctober in vineyards and around late-October in apple orchards. A peak in adult populations were reached between November and December, after which the population dropped drastically from January up to May. P. callosus was the most abundant weevil species and it accounted for 82 % of all the weevils collected during the survey. Other weevils were found in lower abundance: E. occatus (5.9 %), E. setifer (5.8 %), E. chevrolati (2.1 %), P. cervinus (1.9 %), N. leucoloma (1.1 %), T. carinatus (0.4 %), S. tottus (0.3 %), and E .atratus (0.3 %). Most damage took place during the pre-thinning assessment and to a lesser extent in the preharvest assessment. Most of the damage in apple orchards and vineyards was attributed to P. callosus, based on Spearman’s rank correlations, with the remaining weevils contributing to some damage. As it is possible that certain soil physical parameters such as soil texture, soil chemistry and soil bulk density along with the presence of ground cover impact the population of weevils, soil samples were collected in early September, and analyzed for soil chemistry and soil texture. Groundcover surveys and identification took place every two weeks. The results indicated that there was no significant (P = 0.05) relationship between soil chemistry, soil bulk density, soil texture or ground cover percentage and weevil population. The association between adult P. callosus and groundcover was very weak. It is possible that other factors such as soil moisture, cultural practice within the ground cover, relative humidity and soil penetrability impact the weevil population in apple orchards and vineyards. This study identified and recognized nine weevil species causing damage in vineyards and apple orchards in the Western Cape Province, South Africa, of which one was recorded for the first time in vineyards, as well as assessing the effect of abiotic and biotic attributes towards the population of weevils on these crops. The findings of this study aimed towards supporting the development of ecologically-based control strategies; which enable further research into sustainable and integrated approaches to the management of these weevils.


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