DEVELOPMENTS AND IMPLICATIONS
IN THE MANAGEMENT OF INSECT
PEST INFESTATIONS IN STORED
MAIZE, ZEA MAYS (L.): A
CONTRIBUTION TO INTEGRATED
PEST MANAGEMENT
Dr. Costancia P. Rugumamu
Department of Zoology and Wildlife
Conservation,
University of Dar es Salaam,
P.O. Box 35064 DAR ES SALAAM,
TANZANIA
Introduction
 Insect pest infestations cause greater losses of
stored maize crop in developing countries
including Tanzania - hindering agricultural devpt.
 In cases of pest outbreak, the stored crop is at high
damage risk given the low EIL.
 Devpts. in crop insect pest magt. technologies:
applications of chemical pesticides, biological
control, varietal resistance, traditional control,
legislative strategies.
Introduction cont.
 Food and agriculture policy in Tz is to achieve
self-sufficiency in food and food security through
increased food production as well as increased
commodities for export.
 It underscores the need to utilize S&T in order to
maximize productivity:improved methods of
farming, seed varieties & better methods of crop
pest magt. in storage.
 Some technologies are integrated and hence
become components of IPM.
Introduction cont.
 Regarding
GMCs in Tz., preparations are
underway and a National Biotechnology Advisory
Committee (NBAC) has been established.
 NBAC consists of policy makers, govt. agencies,
R&D institutions, and the private sector.
 Advisory on introduction & development of
GMOs in the country= account human and
environmental safety, public concerns, ethical, and
socio-economic factors.
Maize and insect pest infestations
 Maize, Zea mays was first introduced in Tz by
Portuguese traders in the C16th and C17th and was
initially suited to the coastal strip.
 Technological devt. and introduction of many new
maize varieties to farmers has triggered the crop
propagation into the high and middle altitudes.
 Maize as a staple food and cash crop is grown and
stored in almost all the regions of the country.
 The crop however, is mostly susceptible to insect
pest infestations.
Maize and insect infest. cont.
 Since the early 1980s problems associated with
maize storage in Tz have been aggravated by the
accidental introduction of a serious alien pest of
drying maize in fields and in storage, the LGB,
Prostephanus truncatus (Horn).
 LGB was given various local names reflecting
economic losses caused by both larvae and adults
to on-farm stored maize.
 It is imperative therefore to develop effective magt
strategies against the pests especially in rural areas
with agricultural based livelihoods.
Maize and insect pest infest.
 Increases in maize yields have been facilitated by
S&T advances in breeding for genotypes of
greater resistance to field pests and diseases and
by applic.of modern farm practices & implements.
 However, greater storage losses may also result
from some of the improved technologies.
 Some grain physical and chemical/nutritional
characteristics incorporated in breeding could
result into its susceptibility to insects in storage.
Application of chemical pesticides
 Historically, when synthetic chemical pesticides
came into widespread use in the 1940s they
promised an era of abundant agricultural yields,
however, it didn’t take long to recognize that the
miracle chemicals had also costs and risks.
 Chemicals were highly toxic to most insect
groups, broad spectrum and persistent.
 However, despite their shortcomings current
control of stored pests is mainly achieved by
chem. pesticides eg. Permethrine; Pirimiphos methyl.
Application of chem. pesticides cont.
 Insect growth regulators (IGR) and juvenile
hormones (JH) are included in the pesticides
group, they are specific and have minimal
disruptive effects on the environment.
 JH if applied to full-grown larva disturbs
metamorphosis and the insect dies as a deformed
pupa/adult.
 IGR - not as specific as JH but interfere with
cuticle formation at ecdysis killing larvae.
Application of chem. pesticides cont.
 Chemical pesticides in Africa, for example, are
very expensive and most govts. have reduced
subsidy to farm inputs especially to pesticides.
 However, it is argued that many chem. pesticides
may cost comparatively little, because the risks
and social costs associated with their use are not
included in their price.
 Rational decision to use chemical pesticides must
be based on cost – benefit analysis and EIA.
Application of chem. pesticides cont.
 Chemicals rarely kill all the pests, the few
survivors over generations develop slight genetic
differences = biotypes resulting into serious
problems= resistance to the chems.
 If not well monitored, continued addition of chem.
= general ecological disturbance.
 In Tanzania, TPRI supervises & regulates the
manufacture, importation, distribution, sale & use
of pestic. & administer regulations made under the
Act establishing it.
Biological control
 Another IPM component which broadly includes
all control types involving living organisms.
 It reduces the necessity of using chem. poisons
and gives long-term control from one introduction.
 Hence biointensive IPM is advocated under farsighted agricultural policies.
 A natural
predator, the histerid beetle
Terestriosoma nigrescens Lewis was released for
biological control of P. truncatus (Horn) in East
Africa notably in Kenya.
Biological control cont.
 Some limitations to this technology are that,
most predators are not host-specific;
 The enemy requires longer period to be
effective in the control.
 Further ecological research on specificity of
agents to the pests may allow a wide
introduction of more predators; pathogens;
parasites and parasitoids of common insect
pests.
Biological control cont.
 Male sterilization - effective in restricted popns. &
also in spps. where females only mate once and
unable to discriminate against sterilized males.
 Attractant pheromones used in P. truncatus pest
popns. monitoring in Tz. = control measures may
then be exercised with precise timing.
 Pheromones employed in insect pest behavioural
control = induced to fly to inappropriate hosts.
Biological control cont.
 Genetic engin., Tz has ratified the Cartagena
protocol on biosafety - Safe CFTs of GMCs
principles are outlined.
 Under GMO technology, many food plants are
being genetically engineered to resist pests that
include Bacillus thuringiensis, (Bt).
 TPRI & NBAC - closely monitor the devt. &
testing of GM products & provide scientific
advices on their safety.
 However, there are no laws in Africa at present
requiring GM labels on food containers.
Biological control cont.
 Main advantages of biological control
evolve around:
 - no development of resistance by the pests;
 - no residual of poisons in the envt.
 - no build-up of toxins in food chains;
 - no killing of beneficial organisms;
 - permanence of successful control;
 - self-adjusting.
Biological control cont.
 There can arise shortcomings, eg. most
predators are not host-specific, attack
beneficial organisms and the GM parasites
or pathogens when misused cause disasters.
 The dual-use nature of biological agents due
to the ease with which they could be
directed to antagonistic use against crops
and animals raises concern.
Varietal resistance
 It has adverse effect on the bionomics of the pest
by causing its death or decreasing the rate of its
development and reproduction.
 It is environmentally safe, economically
acceptable to farmers and most compatible with
other IPM components.
 A search to identify more insect pests resistant
varieties is recommended as an initiative to
significantly reduce losses.
Varietal resistance cont.
 More methods for screening maize for varietal
resistance are being developed.
 These are intended to positively contribute to the
welfare of communities.
 And to be in line with the need to monitor possible
misuse of breeding technologies which could lead
to mass production and distribution of varieties
with poor storage qualities causing great losses
leading to famine and insecurity.
Application of traditional pesticides
 Farmers’ ingenuity has enabled them through time
to employ IK by applying botanical & nonbotanical pesticide materials to protect their crops.
 In some traditional beliefs seeds are “blessed” by
local priests for high yields, protection from all
types of pests including thieves.
 There is need for further research on the efficacy,
full potential & possible toxicological hazards
associated with traditional pesticides use.
Legislative Control
 Restrictions of movement of produce domestically
& at international entry points are practiced in Tz.
 This programme is adaptable as a model for other
countries in Africa to prevent P. trucatus
infestation from spreading to neighbouring
countries.
 The strategy, however, works with limited success
given free movement of people in these areas.
A way forward in stored products IPM
 Continued research in the field of IPM that will
reduce reliance on only chemical control in farm
stores is recommended.
 Since IPM strategies are specific to each pest,
climatic conditions and other local factors, they
require long term multidisciplinary research
programmes to develop successful methods which
once formulated, IPM strategies unlike chemicals
can’t be packed and sold everywhere.
A way forward cont.
 It is advanced - instead of IPM “technology
transfer” through training and visit (T&V) system,
the “farmer first” paradigm of participatory
nonformal edn. led by IPM extensionists in farmer
field schools followed by community IPM
activities emphasizing farmer-training-farmer &
research by farmers had greater success in
achieving IPM implementation.
 When wisely used and in accordance with BTWC
the S&T advances in stored products IPM would
contribute to solving major development issues.
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