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Class
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Insecta
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Order
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Coleoptera
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Family
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Scarabaeidae
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White grub is a
widespread pest but damage levels are usually low and do not require control
measures. In some locations, damage may be highly significant.
Global.
The larvae live in the soil and gauge broad, shallow cavities in
the storage roots. Damaged roots are not suitable for market or storage,
but may be fed to stock.
There is unclear evidence of larval feeding causing yield
reduction, but in some cases damaged storage roots may decay before harvest.
Usually only a few percent of roots are damaged, but in heavily
infested areas damage may be greater than 50%.
The larvae
have a large, fleshy, white to translucent body with a brown head capsule and
large jaws. They have conspicuous large brown legs on the thorax.
They usually curl into a C-shape when exposed.
White grubs attack a wide range of host plants, and may breed in
fallowed land on weeds such as Chenopodium and Amaranthus species.
They may complete two generations within a sweetpotato crop, allowing population
build-up as the crop matures.
Adults feed on foliage, and are regarded as pests of several
crop and ornamental species, but do not appear to significantly damage
sweetpotato vines.
Grubs are often exposed during weeding operations or during land
preparation.
Removal of grubs by hand during land preparation or weeding may
reduce damage.
Cultivars vary in their susceptibility to attack.
Varieties bred for resistance are available in some countries.
Chemical control is difficult. Frequent applications
(weekly to monthly) are usually required and only give limited control.
Some promising studies have been made of biological control
agents. Suzuki et al. (1994) achieved considerable control using the toxin
from Bacillus thuringiensis serovar japonensis (strain Buibui),
which is specific to Scarabaeid larvae. Yokoyama et al. (1998) found that
the pathogenic fungus Metarhizium anisopliae effectively controlled a
number of grub species, and showed good field persistence.
Ames,
T., Smit, N.E.J.M., Braun, A.R., O’Sullivan, J.N., and Skoglund, L.G. 1996.
Sweetpotato: Major pests diseases, and nutritional disorders. International
Potato Center (CIP). Lima, Perú. 152 p.
Gol'berg, A.M., Avigdori-Avidov, H. and Nuriel, E. 1989. Insecticide
control of a white grub, Maladera matrida, on sweet potato.
Phytoparasitica 17, 175-183.
Jones, A., Schalk, J.M. and Dukes, P.D. 1987. Control of soil insect
injury by resistance in sweet potato. J. Amer. Soc. Hort. Sci. 112,
195-197.
Suzuki, N., Hori, H., Tachibana, M. and Asano, S. 1994. Bacillus thuringiensis strain Buibui for control of
cupreous chafer, Anomala cuprea (Coleoptera: Scarabaeidae), in turfgrass and
sweet potato. Biological Control 4, 361-365.
Yokoyama, T. Hasegawa, M., Fujiie, A., Sawada, M. and Noguchi, K. 1998. Microbial control of scarab beetle
larvae by a formulation of Metarhizium anisopliae (Deuteromycotina:
Hyphoomycetes) in a sweet potato field. Applied Entomology and Zoology 33,
215-218.
Contributed
by:
Jane O'Sullivan
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