Diversity and ecology of phytophagous weevils in the deciduous fruit industry, South Africa
Date
2019-03
Authors
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Publisher
Stellenbosch : Stellenbosch University
Abstract
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.
AFRIKAANSE OPSOMMING: Geen opsomming
AFRIKAANSE OPSOMMING: Geen opsomming
Description
Thesis (MScConsEcol)--Stellenbosch University, 2019.
Keywords
Weevils, Phytophagous insects -- Ecology, Apples -- Diseases and pests -- Identification, Grapes -- Diseases and pests -- Identification, Fruit -- Breeding, UCTD