MANAGEMENT OF STEM BORERS ON SOME QUALITY PROTEIN MAIZE VARIETIES

Four Quality Protein Maize (QPM) varieties: Dent, Sakatifu, Flint, Sammaz 14 and TZEE (Local Check) were evaluated for their response to stem borers. Furadan 3G was applied at the rate of 20 kg/ha at planting for the control of the stem borers. The stem borers damage was assessed by determining the number of leaves with ‘windows’ and plants with ‘deadhearts’. The number of exit holes and tunnels on the stem were also determined and the tunnel length measured. Varieties Dent and Sakatifu had more windows, deadhearts, exit holes, tunnels and longer tunnel lengths than varieties Flint and Sammaz 14. The Furadan treatment reduced the borers infestation and increased the yield of the QPM varieties. Varieties Sakatifu and Dent were found to be more susceptible with tunnel lengths of 8.17 and 5.53 cm respectively. Sammaz 14 and Flint were found to be more tolerant to the stem borers infestation and gave the best yields of 3.19 and 2.95 tons/hectare respectively which were not significantly different from TZEE (check).


Introduction
Maize (Zea mays L.) is an important cereal crop widely grown for food and as livestock feed.Maize ranks with wheat and rice as one of the world's chief grain crops.Maize is native to the Americas and was the staple grain of the region for many centuries.The global production of maize is estimated to be about 300 million tons per year.In Nigeria, its production is quite common in all parts of the country, from the north to the south, with an annual production of about 5.6 million metric tonnes (Central Bank of Nigeria, 1992).Land area under maize has increased from 653,000 ha in 1984 to its present level of 5 million hectares.Production has also increased from 1 to 7 million metric tonnes during the same period.Average yield of 1.5 t/ha being obtained is low compared to other places.Analyses of the increased production from 1984 have shown that the increase was due more to increase in land under cultivation rather than intensive cultivation.A number of factors could have been responsible for the low productivity.These include little or no use of improved seeds, outbreak of pest and diseases, etc. (Moseman, 2008).
Quality Protein Maize (QPM) is another variety of maize that was originally developed by the International Maize and Wheat Improvement Center (CIMMYT) in the late 1990s (Gupta et al., 2009).The high consumption of maize by the human population and the well-established lysine and tryptophan deficiencies in maize protein motivated researchers to develop the QPM to increase the amount/levels of these essential amino acids in its protein.
Newer varieties provide higher protein content (18%) by increasing the prolamine (zein) fraction in maize endosperm.An example of QPM is opaque-2 maize, Sammaz 14, Sakatifu, etc. QPM varieties have almost double the percentages of lysine and tryptophan compared to normal maize, but similar in overall protein content.However, the QPM varieties have a greatly reduced amount of the major storage protein, zein.The biological value of common maize is 45%, whereas the QPM is about 80%.Hence the production and consumption of QPM in countries that use maize as their chief grain crop would have a beneficial effect on the nutritional state of the people and significant economic implications from the better use of what is produced and consumed (Latham, 1997).
The factors which limit maize production are diverse, and insects, particularly the stem borers constitute the most important biotic constraints.The species that are destructive to maize are the maize stalk borer Busseola fusca (Fuller) and the pink stalk borer Sesamia calamistis (Hampson), both Noctuidae, and two pyralids, Chilo partellus (Swinhoe) and Eldana saccharina (Walker) (Wood and Ambridge, 1996).The three species of stem borers, Sesamia calamistis, Eldana saccharina and Busseola fusca are of economic importance to maize in West and Central African regions, while the African stem borers (Busseola fusca) is found commonly in the Cameroun mid-altitude region.Both Sesamia calamistis and Busseola fusca attack maize early in the life of the plant while Eldana saccharina is a late infesting borer.In the low land region of West and Central Africa, stem borers population build-up would generally reach very high damaging levels in the second season.
Stem borers initial damage is caused by feeding on the leaf tissues, followed by tunnelling and feeding within the stem, and sometimes the maize cobs.After hatching, the first instars move into the leaf whorls where they feed and develop on the bases of the leaves, causing lesions.The late third or earlyfourth instars bore into the stem, feeding on tissues and making tunnels.When the infestation is severe, the larvae, either in the leaf whorl or in the stem, can cut through the central leaves which dry up to produce the 'deadheart' symptom, resulting in the death of the plant.A number of studies in eastern Africa have demonstrated a strong relationship between maize yield and damage caused by artificial infestation of stem borers.Ajala and Saxena (1994) studied the relationship among damage parameters such as foliar damage, deadhearts (%), stem tunnelling, morphological parameters such as plant height and number of ears per plant, and their influence on grain, after artificial infestation of three-week-old maize plants, with 30 first-instars.Reduction in the number of ears harvested due to larval infestation was found to be the primary cause of grain yield loss, mainly due to stem tunnelling of the plants.Yield losses were estimated to fall between 34% and 43%.Alghali (1992) showed that yield loss due to stem borers damage is influenced by the cultivar, and by the time and number of larvae involved in infestation.Seshu Reddy and Sum (1991), found a linear relationship between infestation and yield loss, and that the extent of loss increased with earlier infestations.
Planting time can have a significant effect on the extent of yield loss.Studies in Ethiopia, using different planting times under natural infestation, indicate a positive correlation between crop loss and late planting (Gebre-Amlak et al., 1989).Second-generation larvae caused crop losses ranging from 22.5% to 100%, while losses attributed to the first generation were only 0% to 22.6%.A study under natural infestation in three sites in Trans Nzoia district (Kenya) estimated the crop losses at 36.9% under recommended farm practices (Mulaa, 1995).Songa et al. (2001) observed that stem borers damage greatly reduced maize yield with tunnel lengths greater than 20 cm causing a 40% potential yield loss.A 33% yield loss was found in plants with more than one stem borers exit hole.They also observed that principal component analysis showed that stem borers damage, plant height and stem diameter were key factors affecting grain yield and that regression analysis indicated that 1cm of stem borers tunnel reduced yield by 3.0 g/plant due to damage of a single stem borer.Kumar (1997) observed that resistant materials suffered less leaf damage than the susceptible ones.However, irrespective of the crop species, improved varieties grown with fertiliser were more suitable for the development of Busseola fusca (Amsalu et al., 2007).
This paper reports on the study of the varietal difference in resistance to stem borers and evaluation of the efficacy of Furadan for the control of stem borers on quality protein maize.Two stem borers were encountered in this study: Busseola fusca (Fuller) and Sesamia calamistis (Hampson) but B. fusca was predominant.Because it was difficult to differentiate the damage caused by B. fusca alone, the paper reports on the two stem borers.

Material and Methods
The experiment was conducted under rain fed conditions in 2010 and 2011 at the Institute for Agricultural Research (IAR) farm at Samaru, (11 11'N; 07 38'), in the Northern Guinea Savanna ecological zone of Nigeria.The maize varieties used for this study consisted of four QPM varieties: Sammaz 14, Dent, Flint, Sakatifu and a normal protein maize variety TZEE as the standard check.
The field was ploughed and later harrowed to a fine tilth.Plots were established on the 29 th of June 2010 and 27 th of June 2011.The experiment was laid out in a Randomized Complete Block Design (RCBD) with factorial concept (5 varieties and two levels of Furadan 3G: treated and untreated).The ten treatment combinations were replicated three times.Each plot consisted of 4 rows, 4m long spaced at 0.75m and 0.50m between plants in a row.Furadan3G was applied into the planting hole of treated plots during planting at 20 kg ha -1 (as recommended by the manufacturer).
To assess stem borers (B.fusca and S. calamistis) infestation, 10 plants per plot were randomly sampled between the 3 rd and 4 th week after plant emergence (27 days after emergence).The second sampling was carried out between the 7 th and 8 th week after plant emergence (50 days after plant emergence).Rating and measurements of stem borers susceptibility parameters were made on leaves, stem, and grain yield.The incidence of stem borers damage and its severity was assessed by counting the number of infested plants among the ten plants that were sampled, and the number of infected leaves per plant.Leaves were carefully examined for lesions, windows, eating points, and stem for exit holes.
Three maize stands were sampled per plot at random and the damage on stems was assessed by counting the number of stem borer tunnels and measuring the length of the tunnels in each of the stems.The data were subjected to Analysis of Variance (ANOVA).For count data, squared root transformation was done.The statistical analysis was done on mean plot basis from the means of the treatments.

Results and Discussion
Mean number of affected leaves at four and seven weeks after sowing (WAS) of the QPM varieties in treated and untreated plots screened for stem borers infestation is shown in Table 1.The result showed that there was significantly higher number of affected leaves (windows) in plots not treated with Furadan 3G.The number of affected leaves was also higher at seven weeks than at four weeks in treated and untreated plots.However, there was significant difference among varieties in treated and untreated plots.

Stem damage in treated and untreated plots
The mean number of tunnels, length of tunnels and exit holes on stems of the QPM varieties in treated and untreated plots screened for stem borers infestation is shown in Table 2.The result indicates that the QPM varieties Dent and Sakatifu had higher number of tunnels (3 and 2/plant respectively) on the stems while the QPM varieties Flint, Sammaz 14 and TZEE had only one tunnel per plant.Sakatifu had the longest tunnel length of 8.17 cm followed by Dent 5.53 cm and TZEE 2.00 cm.Flint and Sammaz 14 had a tunnel length of 1.0 cm each.For the mean number of exit holes, Dent and Sakatifu had four and two exit holes respectively while Flint, Sammaz 14 and TZEE had only one exit hole per plant.

Grain yield assessment
The result for grain yield for the five varieties screened for stem borers infestation is shown in Table 3.The result showed that there were differences among QPM varieties for grain yield.Flint had the highest mean grain yield of 3.10 kg per plot and 2.65 kg per plot from the treated and untreated plots respectively with a mean yield of 3.19 t/ha, while Sakatifu had the lowest yield of 1.00 kg per plot from the untreated plots and Dent had the lowest yield of 1.87 kg per plot from the untreated plots with mean yields of 2.10 and 2.67 t/ha respectively.TZEE performed better than all the QPM varieties with grain yield of 3.52 kg per plot and 3.34 kg per plot from the treated and untreated plots respectively with a mean yield of 3.81 t/ha.The severity of damage on leaves was higher in the 7 th week than in the 4 th week.This result is in agreement with those of Kalule et al. (1998), who reported that the effectiveness of Furadan decreased with time.It is also possible that fewer numbers of eggs had hatched by the 4 th week when compared to the 7 th week, resulting in the greater leaf damage observed in the 7 th week.Hugo (2002) already established that it is only after hatching that stem borers begin to feed on the leaves, causing lesions or windows.In the fourth week, the treated plots of Dent and Flint had a lower severity level compared to the untreated plot.This agrees with the reports of Kalule et al. (1998) who reported that Furadan was effective in the control of stem borers.The level of severity for all the treated plots was statistically equal.The untreated plots of Dent, Sammaz 14, and TZEE had a higher level of severity.This result also justifies the use of Furadan in the control of stem borers in this study.
The highest number of exit holes was observed only on the untreated plots of the QPM varieties Dent and Sakatifu with 4 and 2 exit holes respectively suggesting that these QPM varieties could be more susceptible to stem borers infestation compared to the others.The number of tunnels was highest in Dent, followed by Sakatifu and TZEE.The number of tunnels reflects the number of larvae that penetrated the stem while the extent of damage is reflected by the mean length of tunnel.The tunnel length is a measure of susceptibility because the borers feed better on susceptible varieties causing the long tunnels while the tunnels are shorter in the varieties that are tolerant.The mean tunnel length was highest in Sakatifu, followed by Dent and Flint.Flint and Sammaz 14 showed some level of tolerance to stem borers.The results are in accordance with those of Kumar (1994) and Kumar and Asino (1994) who studied the difference between susceptible and resistant genotypes in terms of stem damage and found that susceptible genotypes were distinctly more damaged than the resistant ones.

Table 1 .
Mean number of affected leaves of Furadan 3G-treated and untreated plots at 4 and 7 weeks after planting.

Table 2 .
Stem damage of Furadan 3G-treated and untreated plots of the QPM maize varieties screened at Samaru.

Table 3 .
Grain yield of Furadan 3G treated and untreated plots of QPM varieties screened for stem borers infestation at Samaru.