This study was conducted in order to evaluate leaf powder botanical products of Eucalyptus (Eucalyptus macrorhyncha F. Muell), pawpaw (Carica papaya L.), neem (Azadirachta indica A. Juss) and lantana (Lantana camara L.) against the infestation of maize weevil, Sitophilus zeamays (L.) on stored maize grains. These botanicals were compared with synthetic chemical (Actellic Super Dust) and without insecticides application as controls. All tested plant products performed well in the reduction of live insects during maize storage as compared to the no insecticide application. However, pawpaw leaf powder was the most effective in reducing the number of live insects. Similarly, number of damaged maize seeds was relatively less in grains treated with pawpaw leaf powder. This also reflects on the weight loss where the maize grains treated with pawpaw leaf powder were lowest. The weight loss was also less in grains treated with neem and eucalyptus leaf powders. This study suggests that pawpaw, neem and eucalyptus leaf powders can be used as good alternatives to synthetic pesticides against S. zeamays.
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Maize (Zea mays L.) is one of the major cereal crops produced worldwide (Blackie and Jones, 1993). It is a staple food in many countries throughout Africa, Latin America and Asia. In Tanzania, maize is produced by smallholder farmers contributing about 80% of the total maize production in the country (Mdurma and Ngowi, 1995). Mbeya, Rukwa, Iringa and Ruvuma are the leading maize producing regions in Tanzania (Temu et al., 1995). These regions contribute more than 60% of the total produce (Rwamugira, 1996). However, maize yields in Tanzania are very low due to a number of factors. According to Ngugi et al. (1985) insects are the major pests in all the major maize producing areas of Tanzania. One of the major storage pests is maize weevil, Sitophilus zeamays (Key and Mungereza, 1988), which causes damage to stored maize grain by boring the grains and eating the inner part which reduces maize weight and quality in terms of consumption and germination (FAO, 1985).
Currently, control of the insect largely depends on the use of synthetic insecticides. However, the use of synthetic pesticides to protect maize grain against the attack of grain weevil in storage may cause serious health hazards (Talukder and Howse, 1994), problem of pest resistance and resurgence and is quite expensive to smallholder farmer situation (Iloba and Ekrakene, 2006). Therefore, control programs should rely on the extent possible on safe, low cost and locally available alternative tactics that prevent maize grain losses by preventing storage losses from pests. These facts have drawn researchers interests in plant and plant products as source of pesticides. Plant and plant products are useful and desirable tools in most pest management programs because they are effective and often complement the actions of natural enemies (Schmutterer, 1990; Ascher, 1993). A number of investigators isolated and identified chemical compounds from leaves and seeds of many plant species as potential pesticides. For example, the potential pesticides activities of neem, pyrethrum and tephrosia products have been reported for several insects in storage (Akhtar and Isman, 2004; Greenberg et al., 2005; Mbaiguinam et al., 2006; Iloba and Ekrakene, 2006). The present study was conducted to evaluate the efficacy of locally available botanical products as grain protectants on the feeding response and survival of Sitophilus zeamays. Identification of locally available effective botanicals will provide a sustainable alternative to control storage pests, thus contributing to increased food security in the country.
MATERIALS AND METHODS
The experiment was conducted at the Pest Management Centre Laboratory, Sokoine University of Agriculture, Morogoro, Tanzania from October, 2004 to March, 2005. Clean and well-sieved maize grain of the variety Katumbili was bought from smallholder farmers. They were adequately dried and were not previously treated with any chemicals. The grains were graded manually and only larger grains were used in the study.
Maize weevils were collected from the stored culture on shelled maize in one litre kilner jars at 28-29°C and 65-70% Relative Humidity. Neem leaves, lantana leaves, eucalyptus leaves and pawpaw leaves were collected from the respective plants and dried under the shade for 14 days and ground in a grinder before sieving through a mesh of 0.25 mm pore size. The resultant fine powders were stored in airtight containers and placed in a cool dark place until when needed. The amounts of powder mixed with the maize grain were calculated on a weight of powder/weight of grain (w/w) basis (i.e., 100 g of plant materials/1000 g of maize grain seeds). The synthetic chemical (Actellic Super Dust) used in this study was labeled and sealed in packets. The chemical contains 0.3% permethrin and 1.6% pirimiphos methyl as specified by ZENECA CHEMICAL Ltd., Nairobi, Kenya. Each packet contains 100 g of the chemical enough to treat 90 kg of maize.
Six bottles of which were replicated four times were prepared. In each bottle a total of 100 maize grains (≈38.70 g) were placed. There were six treatments used in this study, viz., no pesticides applied (T0) and Actellic Super Dust (T1) as standards, Lantana camara leaf powder (T2), eucalyptus leaf powder (T3), neem leaf powder (T4) and pawpaw leaf powder (T5). Different pesticides were introduced except in the bottles of the control without pesticide application. Neem, lantana, eucalyptus and pawpaw leaf powders were weighed and introduced into 100 shelled maize grains with moisture content of 12.8% in a vial. The maize grain and pesticides powder of all chemicals were tumble mixed for about 5 min. To each bottle and treatment, 20 maize weevils (10 males and 10 females) were introduced. The bottle was then covered with perforated lid and placed randomly using four replications in a Completely Randomized Design (CRD).
Data on effect of maize weevil in stored maize seeds were collected in each treatment and replication eight times in an interval of seven days for number of damaged maize grain; Weight loss of maize grain; number of live insects and number of dead insects.
All data collected were subjected to Analysis of Variance (ANOVA) procedures (SAS, 1990). Tukey test was used to detect mean differences between treatments. All variables recorded were analysed according to the following statistical model:
where: Yij is the response, μ is the general mean effect, Tj is the jth treatment effect and Eij is the experimental error.
|Table 1:||ANOVA table for Sitophilus zeamays infestation on stored maize grain|
|Table 2:||Effect of pesticides on variables investigated|
|Means in the same column followed by the same letter(s) are not statically significant different (p<0.005) following separation by Turkeys test|
Significant treatment effects were observed for numbers of live insects, damaged grains and weight of maize grains (Table 1). Actellic Super Dust showed superiority in controlling the maize weevil (Table 2). Among the botanicals used in this study, pawpaw leaf powder significantly reduced the number of live maize weevils and had the least weight loss of maize grains. Although not significantly different from other botanicals, pawpaw leaf powder resulted in more dead maize weevils and the least number of damaged maize grains. Botanicals significantly excelled the control of no pesticide application in reducing the number of live maize weevils and weight loss of maize grains.
Results confirm that plant products can be used to protect stored maize grains against S. zeamays. The use of local plant products and other available materials to protect stored crop grains have been reported by other workers (Golobo et al., 1982; Lale, 1995). Golobo and Webely (1980), Keita et al. (2000) and Lale and Mustapha (2000) had advanced that oil products from the neem plant are particularly more effective against insects which lay their eggs outside the grain but less effective against Curculionids which lay their eggs inside the grains. Sitophilus zeamays lays eggs inside the maize grains therefore the present study revealed that the use of plant powders could be applied in the control of S. zeamays. In this study, S. zeamays showed least live maize weevils in maize grains treated with pawpaw leaf powder as compared with other plant materials. The trend of live maize weevils shown in this study was dependent on plant products type.
The use of plant powders could have resulted in higher death of insects as a result of physical barriers effect of the plant materials. This is because the powder has the tendency of blocking the spiracles of the insects thus impairing respiration leading to the death of insects. While feeding on whole grains, S. zeamays picks up lethal doses of the treatment thus resulting in stomach poisoning. Schmutterer (1990) reported that azadirachtin from neem plant has deterrent, antifeedant, growth disrupting, antiovipositional and fecundity reducing properties on a range of insects. Endersby and Morgan (1991) stated that Azadirachta indica derivations are most effective as feeding poisons for nymphs or larvae of phytophagous insects while lepidopteraous larvae are very susceptible. Therefore, the insect mortality caused by A. indica as reported in the present investigation is probably due to these inherent properties.
Despite the higher number of grains damaged in maize treated with pawpaw leaf powder, the weight loss was low as compared to no pesticide application. This suggests that pawpaw leaf powder exerts better repellent effect and hence reduced maize grain damage. Results also show that despite the high seed damage recorded in both botanical products, the S. zeamays numbers were relatively high in no pesticides application as compared to maize grains treated with botanicals, indicating that insect reproduction and development were impaired in all botanical pesticides. Schmuttere (1990) reported that botanicals have antiovipositional and fecundity reducing properties on a range of insects.
Hall (1980) observed that leaf powder of eucalyptus globules have a short term protection to rice against S. oryzae. The leaves were reported to have a repellent effect, especially on olfactory and gustatory system of weevils. Also it has been observed that the crushed dry Eucalyptus leaves having their repellent smell can be used for effective control of insect pests especially S. zeamays in maize grains. The percent investigation suggests that pawpaw, neem and eucalyptus leaf powder can be used as good alternatives to synthetic pesticides against S. zeamays due to low maize weight loss recorded in this study.
The authors wish to thank the Government of Tanzania through the Ministry of Higher Education, Science and Technology for financing this study.