The main aim of this study was to gather information on species diversity, host range and ecology of lepidopteran stem borers in selected vegetation mosaics of cultivated and wild habitats in Ethiopia. The findings were projected to provide understanding on ecological interactions of stem borers and their associated host plants in relation to habitat fragmentations. The study further examined the genetic relationships of the Ethiopia populations of economically important sugarcane stem borers with populations in other parts of the continent and abroad. To provide background information to the study, one additional objective on farmers’ perceptions of stem borer pests, their farm management practices, and challenges that hinder adoption of stem borer pest management practices were gathered through interviews. This chapter summarizes the major findings of the studies presented in the previous chapters and indicates areas for future research.
In Ethiopia stemborers constitute a major constraint to maize, sorghum and sugarcane production (Tefera et al., 2004b; Assefa et al., 2008; Goftishu et al., 2017). Grain yield losses in the country due to stem borers generally range from 20-50% (Getu et al., 2008; Wale et al., 2006a; Demissie et al., 2011). Similarly, loss assessment study undertaken in commercial sugarcane estates of the country also revealed that stem borers significantly limit cane and sugar yield by 25 and 34%, respectively (Mengistu ; Selvaraj, 2013). The amount of food made unavailable to humans through stem borer pest infestations is quite substantial and calls for effective management. Accordingly, various stem borer management practices, such as, cultural practices particularly crop residue management (Gebre-Amlak, 1988; Dejen, 2004), intercropping (Tsehaye et al., 2007; Wale et al., 2007; Belay et al., 2009), trap cropping (Belay ; Foster, 2010), and modification of planting dates (Gebre-Amlak et al., 1989; Dejen, 2004); several synthetic (Getu et al., 2008) and botanical insecticides (Dejen, 2008; Dejen et al., 2011; Tilahun ; Azerefegn, 2013; Wondimu ; Dejen, 2014) and natural enemies (Dejen et al., 2013) have been recommended for minimizing the damage caused by cereal stem borers in the country.
Interviews held with small-scale farmers indicated that stem borers were considered as major constraints for the production of maize and sorghum in the study area. Farmers estimated yield losses due to stem borers ranging from 10 to 50% (Chapter 3.1). Although scientists have devised and recommended several alternative methods of borer management, these technologies have been largely ignored by subsistence farmers in the region (Chapter 3.1). Large gaps still exist between research findings and farmers’ practices. Few pest management practices were employed by some farmers, still the majority of maize and sorghum crops were left unprotected and suffering from the damage incurred by stem borers. Most of the farmers interviewed in this study indicated that they were aware of the type and application method of insecticides. But, due to high cost and non-availability, farmers did not apply insecticides for the control of stem borers (Chapter 3.1). The majority of smallholder farmers in the region traditionally practice intercropping and other cultural management practices. Cultural control of stem borers is the most relevant and economical method available to millions of resource-poor farmers in SSA (Van den Berg et al., 1998). Even though some effective and low input cultural management methods are available, the study showed that farmers were not implementing cultural management practices in a way that reduces stem borer damage (Chapter 3.1). Furthermore, most of the cultural management components are location specific. Therefore, research recommendations on the management of stem borers should be developed based on local conditions and species of stem borers. The study showed that farmers did not have access to the research outputs of stem borer pest management practices. The extension service is poorly developed and extension agents also lack the necessary technical knowledge to adequately address farmers (Chapter 3.1). Similar studies undertaken in a number of African countries showed that farmers do not have access to technology and innovations generated from research institutes and universities (Lwoga et al., 2011; Serah, 2014). Many farmers in developing countries do not receive extension service training on the proper use of new pest control strategies (Midega et al., 2012). Therefore, improving the level of extension services in the studied areas is of critical importance for establishing effective and sustainable stem borer pest management practices in the region.
This study presents higher stem borer species diversity among wild plants contradicting previous studies in which fewer stem borer species were reported from wild plants (Laporte, 1975, 1976; Rougeot, 1984; Rougeot et al., 1991; Le Ru et al., 2006a). Differences in the number of stem borer species between previous and present study may be attributed to variations in the geographic coverage and sampling methodologies. Previous studies covered few geographic locations. Moreover, in previous studies stem borer samples were collected only from wild host plants (Le Ru et al., 2006a) or light traps (Laporte, 1975, 1976; Rougeot, 1984; Rougeot et al., 1991). However, the present study used both methodologies simultaneously, active search for damage symptoms in the wild host plants and light trapping. Applying these sampling methods together helped to capture both the immature (from wild host plants) and adult (with light traps) stages, which in turn yielded higher stem borer species diversity (Chapter 3.2). Similar combination of approaches had been used in other studies exploring stem borer species diversity in Africa (Nye, 1960; Le Ru et al., 2014).
A total of forty-four stem borer species belonging to 14 different genera in the families of Noctuidae, Crambidae, Pyralidae and Tortricidae were recorded from wild host plants and through light trap. Among these families, Noctuidae was the highest in species richness in which 31 species were identified, out of which 15 species and two genera were new to science (Chapter 3.2). The result confirms that stem borer species diversity in Ethiopia is much higher than earlier reported (Laporte, 1975, 1976; Rougeot, 1984; Rougeot et al., 1991; Le Ru et al., 2006a). Among the vegetation mosaics, the undifferentiated montane vegetation that mainly covers the highlands of Central, South-Eastern and South-Western Ethiopia was the richest in stem borer species diversity. The Ethiopian highlands are source of water to rivers, streams and wetlands, and often referred as the “water tower of Northeast Africa” (Wondefrash, 2003; Williams et al., 2005). In wild habitats, lepidopteran stem borers are mainly found in thick grasses and sedges growing in wetter localities (Le Ru et al., 2006a). Thus, the relative abundance of such habitats in high altitude areas of Ethiopia might have contributed to the diversity of stem borers recorded. Similar to our findings, high diversity of noctuid stem borers was reported in the high-altitude areas of East (Le Ru et al., 2006b; Ong’amo et al., 2013) and Central Africa (Ong’amo et al., 2014). In addition to species richness, the undifferentiated montane vegetation harbored many of the new noctuid stem borer species (Chapter 3.2). The newly recorded noctuid stem borer species are rare in the region and could possibly be endemic to Ethiopia. Similar studies conducted in sub-Saharan Africa also confirmed the presence of a high rate of endemism in noctuid stem borers particularly in the genus Acrapex (Le Ru et al., 2014; Le Ru et al., 2017a, b, c). The Ethiopian highlands are known for their high concentrations of endemic species (Mittermeier et al., 2004; Williams et al., 2005; CEPF, 2012). The great proportion of endemicity particularly in the highlands is attributed to geographic barriers associated with the Great Rift Valley and Pleistocene climatic changes, in which sky-islands acted as long-term refuges and cradles of genetic diversity (Williams et al., 2005; Mairal et al., 2017).
A total of 34 wild host plant species were recorded, which is more than double from the previous reports (Chapter 3.2). Species diversity of stem borers correlates positively with increased plant diversity (Otieno et al., 2006; Moolman et al., 2014). Though, the majority of stem borer species had a limited host plant ranges. Similar host use pattern was reported by Le Ru et al. (2006b) contradicting previous reports in which stem borer pests were considered as polyphagous (Polaszek & Khan, 1998). Similarly, the host plant-stem borer interaction networks exhibited a high degree of network specialization (H2?) and host plant specificity (di’) of stem borers at the community and species level, respectively (Chapter 3.2). From an ecological network perspective, this means that the loss of a plant species most likely lead to extinction of the associated stem borer species in the network (Araujo et al., 2017). If a species is lost from an ecosystem it is not only the species itself that is lost, but its interactions, and the ecological functions that result from these interactions, for example, pollination (Devoto et al., 2011) and natural enemies (Kankonda et al., 2017). The loss of interactions can have prevalent effects on both ecosystem structure and functioning (Rzanny ; Voigt, 2012). Species diversity, network structure and ecosystem functioning are closely related (Harrison et al., 2014). The results of host plant-stem borer interaction network analysis of each vegetation mosaics could be used to determine the stability and resilience of a particular ecosystem (Chapter 3.2). By identifying and quantifying the general patterns of interaction networks, it is possible particularly for network ecologists to describe the structure of networks and draw conclusions on ecological and evolutionary processes (Bascompte ; Jordano, 2007) of interacting species.
Some stem borer species currently restricted to natural habitats may have the potential to shift and become an important pest of cultivated plants since the natural habitat that accommodate their alternative host plants may not persist for long due to anthropogenic habitat disturbance. This is what has happened in many parts of the continent where intensive cultivation is practiced (Conlong, 2001; Goebel ; Sallam, 2011). Adaptation of E. saccharina to sugarcane subsequent to its extensive cultivation in southern African countries (Conlong, 2001; Mazodze ; Conlong, 2003) and host range expansion of S. nonagrioides to sugarcane in Ethiopia (Chapter 4.2) are examples of new associations between indigenous stem borers and sugarcane in Africa.
Three species of lepidopteran stem borers viz., B. fusca, C. partellus and S. calamistis were found attacking maize and sorghum in eastern Ethiopia (Chapter 3.3). Similar to the present result, previous studies also reported the presence of three species of stem borers in maize and sorghum agroecosystems of Ethiopia (Assef, 1985; Getu et al., 2001; Wale et al., 2006b). Busseola fusca and C. partellus dominated the stem borer community. The exotic C. partellus is the most damaging in lowland areas while the indigenous B. fusca is restricted to mid and high-altitude zones. However, the pest status of S. calamistis was low and found in lower and midaltitude zones (Chapter 3.3). Variations in the spatial distribution and economic importance of these species across different ACZs may be attributed to differences in their environmental and ecological niche requirements (Getu et al., 2001; Wale et al., 2006b). High level of borer infestation and larval density per plant were recorded in lowlands followed by highlands. Intermediate level of infestation was observed in mid-altitude zones (Chapter 3.3). The probable reason for the higher level of infestation and larval density in the lowland is related to the biology of the dominant species, C. partellus. Chilo partellus terminate diapause and emerge approximately one month earlier than the other indigenous stem borers found in the region. Moreover, the life cycle of C. partellus is three weeks shorter than the indigenous stem borer, B. fusca (Kfir, 1997; Rebe et al., 2004). Furthermore, the high level of infestation observed in the highlands as compared to midaltitude zone could be due to the long maturing sorghum and maize varieties used in the area. Late maturing varieties had higher infestation because of the extended time of exposure to stem borers allowing more than one generation on the same crop. This agrees with the findings of Van den Berg et al. (1990) and Tanzubil et al. (2002). Knowledge on the distribution and ecological requirement of pest species has been used in the designing of stem borer management plans for different regions (Overholt et al., 1997).
Sesamia cretica and S. nonagrioides (Chapter 4) were recorded from commercial sugarcane plantations located in the Rift Valley of northeastern and central Ethiopia, respectively. These two stem borer species were recorded for the first time on sugarcane in the country. Assefa (2006) recorded B. fusca, B. phaia, C. partellus, and S. calamistis from commercial sugarcane estates (Assefa, 2006). Getu et al. (2001) reported S. nonagrioides botanephaga from sorghum and sugarcane.
Sesamia cretica is considered as a major pest of maize, sorghum and sugarcane plants in North and East Africa (Osman et al., 2014; Alhussein et al., 2015). However, S. nonagrioides has for a long time been associated with wild grasses in East Africa and are here considered as pest of sugarcane in Ethiopia. This is the first report where S. nonagrioides attacks sugarcane in Africa as well (Chapter 4.2). There are two probable explanations for the invasion of Ethiopian sugarcane by these stem borer pests;
i) Even though, S. cretica and S. nonagrioides were initially present on sugarcane in Ethiopia some time ago, they might have been incorrectly identified as S. calamistis or S. peophaga.
According to Moyal (2006), the subtribe Sesamiina is highly speciose and taxonomically complex, so individuals are often difficult to be identified to the species level (Moyal ; Le Ru, 2006a). Incorrect specimen’s identification by researchers from different countries has often occurred, resulting in the publication of misleading information over the years (Polaszek, 1992; Le Ru et al., 2006a).
ii) These stem borers might have been present in wild hosts for long time and recently expanded their diet breadth after the establishment of a sugarcane plantation in the area.
In recent years, the commercial sugarcane estates of Ethiopia are expanding their sugarcane production areas by displacing farmers crop lands, pasture lands, and the natural vegetation. Mass clearing of wild host plants for large scale sugarcane production might be a possible reason for the invasion of sugarcane by stem borers. A similar trend of infestation and spread has been observed in the Mediterranean corn borer, Sesamia nonagrioides that switched from wild host to sugarcane after a massive destruction of natural habitats for large-scale sugarcane production in Iran (Esfandiari & Soleimannejadian, 2012). Several ecological studies have revealed that the introduction of exotic plants can lead to host plant shifts in oligo- or monophagous insect species. This is the case for African cereal stem borers such as B. fusca and S. calamistis which shifted from wild hosts to maize (Haile & Hofsvang, 2002; Ong’amo et al., 2012) and Eldana saccharina, that moved from wild sedges to sugarcane (Carnegie, 1974) subsequent to its introduction to Africa. The destruction of natural habitat to create new sugarcane plantations coupled with intensive agronomic practices and lack of natural enemies plays a major role to the outbreak of insect pests in sugarcane (Conlong, 1997; Goebel ; Sallam, 2011).
Currently, S. cretica and S. nonagrioides is a major pest of sugarcane in Ethiopia. Though, so far, it was not recorded on maize and sorghum crops in the country. However, both species attained a major to moderate pest status on sorghum and maize crops in other parts of Africa, Europe and the middle east (Buadu et al., 2002; De La Poza et al., 2008; Alhussein et al., 2015; Esfandiari et al., 2015). In the same way, these species are likely to adapt maize and sorghum crops and expand their distribution range into new biomes in Ethiopia. Host range expansion to sugarcane and maize by indigenous African stem borers is becoming a common phenomenon (Ong’amo et al., 2012; Assefa et al., 2015; Assefa et al., 2017). Therefore, it is important to monitor the dynamics of stem borer species in cultivated plants, which could make a significant contribution to the management of stem borers in Ethiopia
To investigate the origin of the newly recorded stem borer pests in Ethiopian sugarcane and the genetic relationships of these with populations of the same species, phylogeographical analyses were conducted on Ethiopian specimens collected from sugarcane and wild hosts with populations in other parts of the African continent and abroad.
Phylogeography has been providing considerable information about the historical processes responsible for geographic distribution and genetic diversity of species. Even though, the main focus of phylogeography is on intraspecific genealogies and their relation with geography, history and demography, the approach can also be useful analytical tool in uncovering of cryptic speciation (Avise, 2000). The approach bridges the gap between traditional phylogenetic and population genetics studies. Mitochondrial DNA has been used to reconstruct the phylogenetic and phylogeographic relationships in indigenous stem borers (Assefa et al., 2006c; Sezonlin et al., 2006; Esfandiari et al., 2015). Studying the phylogeography of insect pest species was not only interesting from an evolutionary point of view, but could also provide information useful for defining successful pest management programmes (Kebe et al., 2017).
A phylogeographic study conducted on the populations of S. cretica from five countries viz., Ethiopia, Eritrea, Kenya, Cameroon and Iran revealed the presence of genetic divergence between populations of the pest (Chapter 4.1). The populations were clustered in to two clades. Samples collected from Iran, Eritrea, Kenya and Cameroon grouped together and named as the Afro-Asian clade and the second clade was from Ethiopia. High genetic divergence was recorded between the Ethiopian and Afro-Asian population corresponding to geological events and host plant differences. The populations of each clade were collected from a specific host plant (the Afro-Asian clade from sorghum and the Ethiopian clade from sugarcane and wild host). As a result, it was difficult to distinguish the role of each factor (geological events and/or host plant variation) in the genetic divergence of the clades. One of the greatest challenges in phylogeography is to understand how geography and ecology shape the genetic structure of species (Avise, 2009). Furthermore, the two clades could possess differences in some ecophysiological traits, such as diapause (Kim et al., 2007) and voltinism (Martel et al., 2003; Coates et al., 2004) depending on the seasonal availability of host plants. The Ethiopian population obtained from sugarcane might have multivoltine populations owing to consecutive availability of sugarcane seedlings and ratoons unlike the Afro-Asian population collected from sorghum. The genetic differentiation documented among the two clades was further accompanied by restricted gene flow (Chapter 4.1). Understanding the genetic diversity and gene flow a target pest species is necessary prior to large scale efforts aimed at control of insect pests (Low et al., 2014). Genetically different populations of insect pests vary in their response to various pest management practices (Chen et al., 2012; Joyce et al., 2014). Therefore, based on the observed genetic variation between the two clades, exchange of information with neighboring countries on the management practices of the Ethiopian population of S. cretica may yield nothing or little benefit as the effective tactic against the Afro-Asian population may not be equally effective against the Ethiopian population. Such type of population genetic studies will not only improve our understanding of population genetic structure at a regional level but will also assist the development of sustainable and sound insect pest management strategies.
Among indigenous African stem borers, S. nonagrioides has a wider distributional range and is the most generalist species with 42 known host plants belonging to Cyperaceae, Poaceae and Typhaceae (Le Ru et al., 2006a, b; Kergoat et al., 2015). Studies on such generalist phytophagous insects often reveal that they instead represent complexes of genetically differentiated host races or cryptic species (Martel et al., 2003; Assefa et al., 2006c). Ecological studies on S. nonagrioides have reported the variation in pest status across its distribution range in Africa (Buadu et al., 2002; Moyal et al., 2011b). Previous studies in Ethiopia revealed that S. nonagrioides was recovered only from wild host plants (Le Ru et al., 2006a; Moyal et al., 2011b). In the present study S. nonagrioides was found for the first time attacking sugarcane in Ethiopia in particular and in Africa at large (Chapter 4.2). Moreover, during this study, S. nonagrioides was recorded for the first time from different wild host plants in Botswana, outside its known geographical range. In species with wide geographic distributions and extensive host ranges it is not uncommon to find considerable genetic difference (Seyahooei et al., 2011; Barman et al., 2013). Thus, the newly recorded populations of S. nonagrioides could be genetically distinct from the previously known populations, due to the variation in eco-geographic factors and pest status of the insect across its geographical range (Assefa et al., 2006c). Based on this hypothesis, the biogeography and population genetics study conducted on the populations of S. nonagrioides at the scale of its whole distribution (twelve countries in Central, East, West and southern Africa and four countries from Palearctic regions) revealed the presence of genetic divergence between populations of the pest (Chapter 4.2).
The phylogenetic analyses separated the populations into two major clades. However, a strict geographical separation of haplotypes was not observed between clades. Few haplotypes collected in very close geographic locations were found to belong to distinct clades. The study also argues against the existence of HAD in S. nonagrioides (Chapter 4.2). The first line of evidence for the absence of HAD is the presence of the most common haplotypes on different host plants, in multiple samples, over vast geographic areas. The second line of evidence for absence of HAD is the separation of haplotypes feeding on a specific host plant into different clades. Furthermore, an IBD model is not supported for S. nonagrioides at the continental scale (Chapter 4.2). Estimated divergence time between the two lineages of S. nonagrioides likely related to Pleistocene climatic oscillations, characterized by an intense climatic change in sub-Saharan Africa (deMenocal 2004). This factor was also reported to shape the genetic structure of maize stem borer, B. fusca (Sezonlin et al., 2006; Assefa et al., 2015). The most plausible hypothesis for the observed distribution pattern of S. nonagrioides population might be because of isolation and genetic differentiation within refugia during unfavorable periods and subsequent range expansion during favorable ones, with secondary contact between diverged lineages when overlapping occurred. Thus, S. nonagrioides survived unfavourable periods during the Pleistocene in at least one refuge located in Eastern and one refuge located in Western Africa, with overlapping in the present-day Tanzania. This country, therefore, could be considered as a hybrid or overlapping zone where the two lineages of S. nonagrioides came in contact (Chapter 4.2).
Results of the molecular analysis indicated the host range expansion of S. nonagrioides from wild host plants to sugarcane in Ethiopia (Chapter 4.2). This is further supported by the shared haplotype between the sugarcane and wild host population. The presence of S. nonagrioides on a wide range of host plants and its rapid adaptation to sugarcane without genetic variation suggests the existence of host use plasticity (Ong’amo et al., 2012; Assefa et al., 2017). Moreover, the molecular analysis revealed the long-time establishment of S. nonagrioides in Southern Africa.
Interviews held with small-scale farmers indicated that stem borers were considered a major constraint for the production of maize and sorghum in the study area. Despite this, there were gaps between research findings and farmers’ awareness in stem borer pest management practices. Subsistence farmers cannot afford chemical insecticides for low-value crops like maize and sorghum. As a result, management strategies based on cultural practices are presently the most promising strategy. However, most of the cultural management components are location specific thus, research recommendations on the management of stem borers should be developed based on local conditions and species of stem borers. Moreover, there is a need to create awareness among farmers about the principles and practices of cultural management methods to minimize the damage caused by stem borers.
High diversity of stem borer and host plant species were recorded in natural habitats. The diversity of these species varied among vegetation mosaics and host plants. Borer diversity correlates positively with increased plant diversity. However, the majority of stem borer species were recovered from limited number of host plants suggesting that they are monophagous contrary to previous reports in which they were presented as polyphagous. Many more species may be reported if this kind of study cover Combretum-terminalia woodland ecosystems of western and north-western Ethiopia, particularly known of diverse species of grasses and sedges. The result of this study, particularly host plant-stem borer interaction network analysis of each vegetation mosaics could be used to draw conclusions on ecological and evolutionary processes of interacting species, stem borers and host plants (Chapter 3.3).
Three species of stem borers were recorded from small-scale farmers’ fields of maize and sorghum crops in eastern Ethiopia. Among these, B. fusca and C. partellus were the most important species. Surveys undertaken in sugarcane estates found the presence of two lepidopteran stem borer species viz., S. cretica and S. nonagrioides on Ethiopian sugarcane. Sesamia cretica was found from Tendaho sugar estates located in the northeastern part of the country, while S. nonagrioides was recorded from three sugar estates in the central part of Ethiopia. These species were reported for the first time from Ethiopian sugarcane. Probably these species might have expanded their host range to include easily available and more nutritious cultivated crop sugarcane in response to habitat modification. Host range expansion of these species to sugarcane and their record to the pest community provide evidence of a significant risk of emergence of new sugarcane pests. The addition of new stem borer species to the pest community would complicate the existing stem borer pest management practices. Therefore, conservation of ecologically important natural habitats has paramount importance to delay host range expansion/shift of stem borers to cultivated plants and for provision of ecosystem services. Data from these surveys could be used to examine changes in the distribution of stem borers, their host plants and for the planning and implementation of stem borer management strategies.
The present study is the first molecular phylogeographic study of S. cretica. Results of the sequence analysis revealed the existence of genetic diversity among populations of S. cretica collected from different parts of Africa and the middle east. The study also revealed the presence of S. cretica on sugarcane in north-eastern Ethiopia. So far, the species was not recorded on cultivated crops from other localities in the country. However, it attained major pest status on sugarcane, maize and sorghum crops in various African countries. Consequently, with the change in climate and intensification of agriculture, the chance of this pest adapting maize and sorghum crops in Ethiopia could also be high. Such type of phylogeographic study not only improve our understanding of population genetic structure at a local level but also assist for developing sustainable and sound insect pest management strategies.
This study represents the comprehensive investigation of the global-scale phylogeography of S. nonagrioides. The study provides the first evidence that S. nonagrioides invading sugarcane in Ethiopia. Furthermore, the study revealed the presence and long-time establishment of S. nonagrioides in Botswana for the first time. The pest did not exhibit host associated genetic variation. Tanzania was suggested to be a hybrid or overlapping zone for S. nonagrioides populations in Africa. Results of this study assist in understanding the evolutionary forces that may be responsible for the spatial distribution, genetic divergence and host range expansion of S. nonagrioides population. The genetic differences in S. nonagrioides population should be carefully considered while designing pest management strategies. Furthermore, sugarcane farmers in sub-Saharan Africa should be aware that S. nonagrioides has moved from wild hosts to sugarcane in Ethiopia. Thus, they should be advised to monitor sugarcane farms and take the necessary measures to prevent/delay invasion by S. nonagrioides.
Since this study was not exhaustive, and based on the present conclusions, the following recommendations are made for future studies.
• Awareness should be created among farmers about research findings and recommendations made on the management of cereal stem borers. Moreover, effective and low input stem borer management strategies should be developed based on subsistence farmers’ needs and priorities by taking their crop production practices into account.
• The distribution and diversity of stem borers would be expected to be dynamic, particularly with the anticipated climate change and habitat fragmentation. Thus, periodic update on the diversity, distributions and host plant interactions of stem borers both on cultivated and natural habitats should be conducted in representative agroecosystems of the country.
• To fully comprehend the role of natural habitats in stem borer pest dynamics, host plant-stem borer-natural enemies’ interactions should be investigated at representative agroecosystems of the country.
• As mtDNA is maternally inherited, the degree of paternal gene flow remains unknown, and may have consequences in studies of species exhibiting sex-biased dispersal patterns. Further research is needed by using both mitochondrial and nuclear DNA markers in order to make more reliable conclusions about male and female migration and gene flow estimations among populations of S. cretica.
• The phylogeographic study of S. cretica were challenged by sampling size. Therefore, to obtain an in-depth biological information on the evolutionary history of the pest in Ethiopia, it is imperative to sample more specimens both from cultivated and wild hosts from Ethiopia and other countries, particularly from the neighboring countries such as Sudan and Somalia where the pest is economically important.