Château-Musa - Bioversity International

Thesis
by the environmental conditions. There was a
stagnation in the number of egg-laying females
in the roots during the cold and dry season but
no decline. No effect of the nematodes on plant
52
growth was found. The number of nematodes
in the roots seemed related to the physiological
stage of the plants. The highest nematode
numbers were found during flowering.
Components of a strategy for the integrated management of the
banana weevil Cosmopolites sordidus (Germar) (Coleoptera;
Curculionidae)
Stijn Messiaen
PhD thesis submitted to Katholieke
Universiteit Leuven, Leuven, Belgium. 2002.
The study was conducted at the Centre
Africain de Recherche sur Bananiers et
Plantains (CARBAP) in Cameroon, with
funding of the Flemish Association for
Development Cooperation and Technical
Assistance (VVOB) and in association with
INIBAP and KULeuven.
The banana weevil Cosmopolites sordidus
(GERMAR) is found in all banana and plantain
producing areas in the world. Its larval stage,
spent feeding inside the corm of bananas
and plantain, is a major constraint to
resource-poor farmers in West and Central
Africa, for whom bananas and plantain fulfil
a vital role in food security. Since current
research results suggest that no single
control strategy will be likely to provide
complete control of the banana weevil, a
broad integrated pest management program
might provide the best chance of success in
controlling this pest.
The objective of this thesis was to study
components of banana weevil control
strategies, for future implementation on-farm
within the framework of a strategy of integrated
management. The components studied in this
thesis, determined by banana weevil research
priorities at CARBAP, attempted to address
banana weevil IPM technology and knowledge
gaps and consisted of certain aspects of
host-insect interactions, botanicals, chemical
control and genetic control.
Different parameters used for monitoring
weevil damage were analysed and compared
because considerable doubt remains among
farmers and researchers on the reliability of
the different parameters for monitoring weevil
damage. It was shown that assessment of
peripheral weevil damage on the corm of
30 plants per ha is a reliable alternative for
assessment of the more important cross
section weevil damage in the central cylinder
of the corm, which is better related to growth
and yield but requires destructive sampling.
In contrast, assessment of a percentage
of attack based on the number of plants
infested is an unreliable parameter because
it requires a lot of sampling and because
occurrence of weevil damage inside or in
the underground part of the corm can lead
to serious errors.
The population dynamics and yield loss
study on the plant crop of plantain indicated
that a banana weevil population can build up
from a small leftover weevil population to more
than five weevils per mat within the first plant
crop, thereby significantly reducing growth and
yield. This high rate of increase of the weevil
population contrasts with other field studies
in older plantations but corroborates with the
observed fecundity potential of banana weevils
under laboratory conditions.
In the field, the banana weevil population was
most active in the wet season, which indicates
that control measures targeting the adult stage
should be conducted primarily in this season.
For the first time in banana weevil research, it
was shown that weevils do fly in the field, and
that this could constitute an important source of
infestation, which has important implications in
terms of banana weevil management.
High rates of death of young plants due
to weevil damage in plantain field trials
indicated that integrated pest management
strategies should aim in the first place at the
protection of young plants, in order to ensure
minimal premature death and optimal plant
development in the first months after planting.
It was shown that weevils, besides nematodes
and insufficient anchorage, can also contribute
to toppling. Weevil damage was shown to
affect growth, yield and plant crop duration.
Compared to undamaged plants, plants with
heavy banana weevil damage were 15%
shorter, had a 33% smaller bunch and took 8%
more time to reach harvest.
Of the different control strategies tested,
neem (Azadirachta indica) seed powder
InfoMusa - Vol 12 - No.1