**2.4 Major insect pests of maize**

Globally, insect pests are categorized into two classes; (1) field pests such as stalk borer (*Busseola fusca*), maize leafhoppers (*Cicadulina mbila*) and mole crickets (*Gryllotalpidae*), African bollworm (*Helicoverpa armigera*), African armyworm (*Spodoptera exempta*) and black cutworms (*Agrotis ipsilon*) and (2) storage pests like the maize weevil (*Sitophilus zeamais*), larger grain borer (*Prostephanus truncatus*) (Hon), red flour beetle (*Tribolium castaneum*) and dried bean beetles (*Callosobruchus maculatus*) and Indianmeal moth (*Plodia interpunctella*) [54].

The most important arthropod pests of maize in Europe is known as European corn borer, *Ostrinia nubilalis* (Hbn., Lepidoptera: Crambidae). The lepidopteran larvae (i.e., caterpillars) known as stalk borers, ear or leaf feeders, and coleopteran larvae (i.e., beetle grubs) that feed on roots. The European corn borer is a nicknamed the "billion dollar bug" because it cost growers over a billion dollars annually in insecticides and lowers crop yields [56, 57]. It is known globally to cause enormous economic damage. While in America the borer mostly found include the genera Zeadiatraea*,* Diatraea and Elasmopalpus*.* The western corn rootworm (*Diabrotica virgifera virgifera* LeConte), a chrysomelid beetle is known to be the most destructive for maize production in the USA, Hungary and other central and eastern European countries [58]. While in Africa the following pests are associated to this region; *Chilo*, *Sesamia*, and *Busseola*, and in Southeast Asia *Chilo*, *Sesamia* and *Ostrinia furnicalis* are present in their maize fields. While damage is mainly caused by the larvae feeding on roots, adults feeding on silk and ears may cause additional losses, particularly in maize production for grain, seed or food (sweet maize). Sap sucking pests, like aphids (Aphididae) and leafhoppers (Cicadellidae), as well as the frit fly (*Oscinella frit* L.) cause limited economic damage as compared to the european corn borer. Other pests of regional importance include armyworms such as *Pseudaletia unipuncta* (Haworth, Lepidoptera: Noctuidae), Diptera species such as *Delia platura* (Meig.), *Geomyza* spp. and *Tipula* spp., Coleoptera species such as *Oulema melanopus* L., *Glischrochilus quadrisignatus* (Say), *Tanymecus dilaticollis* Gyll. and *Melolontha melolontha* L., spider mites (*Tetranychus* spp.) and thrips (Thysanoptera) [59].

#### **2.5 Maize disease and Pest management**

#### *2.5.1 Planting resistant varieties*

One of the most reliable method of controlling plant disease is planting of resistant varieties [60]. It is one of the most attractive approaches and can be considered as an ideal method if good quality plants are adapted to the growing regions with sufficient levels of tolerance and durable resistance This method is considered ideal and mostly used in many crops because its less expensive as compared to pesticides cost and residual effects on man, animals and the environment. Although its economical as compared to pesticides, these resistant varieties often take decades to develop and GM-plants suffer from extremely high regulatory approval cost and consumer acceptance. Its ultimately used by farmers provided quality plants are selected and adapted to exhibit adequate levels of tolerance and substantial resistance to pathogens [61]. Inspite of its advantages, it is faced with some backlash as regards the time in developing Genetically Modified (GM) plants, cost of approval and acceptance rate by customers. There have been also cases where resistance breakdown was recorded in several crops coupled with pathogens mutating their virulence gene, inconsistent uniformity in the genetics of the plants. Such cases were observed in cotton leaf curl disease [62].

#### *2.5.2 Chemical control*

Agrochemicals have been adapted over the years to secure food production and improve crop yield thus protecting crops from pests and pathogens. Since the 1960s, there have been an increase in pesticides use. They help in preventing losses and damages of crops; it has now become an integral component in Integrated Pest Management (IPM) [63]. It cannot be overemphasized the advancement that pesticides have brought to the agricultural sector as regards improving crop quality and annual agricultural output [64]. Nevertheless, the development of resistance genes by pathogens and pests coupled with the growing concern of accumulation off these chemicals in feeds and the ecosystem has been a great concern to farmers [65, 66].

#### *2.5.3 Biological control of pathogens*

Heimpel and Mills [67] defined biological control of plant diseases to be the suppression of the populations of plant pathogens by the use of living organisms. In plant pathology, beneficial organisms (crops, insects and microorganisms) are selected to diminish the effects of pathogenic organisms and improve the crop yield microorganisms. Other examples of biological control include the application of natural products and chemical compounds extracted from different sources, such as plant extracts, natural or modified organisms or gene products control [68]. This method was developed to minimize the dependence on agrochemical use and the risks for human health and the environment [69].

There are various interactions between plants, biological control agent and pathogens, they include mutualism, commensalism, neutralism, competition, amensalism, parasitism, protocooperation and predation [70–72]. The interactions between the microbes and plants occurs naturally at both macroscopic and microscopic level [68].

#### *2.5.4 Cultural/traditional insect Pest control*

Timely harvesting, proper harvesting and processing methods are the best strategy for controlling insect pest in maize. Proper sanitation, removal of old stock, avoid storing infected crops inside the storage facility. Other methods used by farmers to reduce infestation of maize by insect pest include the use of material such as ashes (it is known to abrasive and lethal effect on the insects' cuticle), sand, crushed limestone, mineral and oil in which physical barrier effects are responsible for the control of insects, storing dried maize that are properly dried or re-drying when infestation is detected, the use of sheaths in storing maize for protection by the husk, the use of repulsive local herbs and plants to scare off the pests (Nim ground seed, leaves of acanthaceae, acardiaceas, annonaceae, myrtaceae, other plants extract [73].
