Sam Korie

Effectiveness of Spinosad Bait Sprays (GF-120) in Controlling Mango-Infesting Fruit Flies (Diptera: Tephritidae) in Benin

ABSTRACT Effectiveness of GF-120 (Dow Chemical) Fruit Fly Bait containing the insecticide spinosad in controlling mango-infesting fruit flies (Diptera: Tephritidae) was assessed by comparing treated orchards with untreated orchards. Twelve mango, Mangifera indica L., plantations located in six villages (two similar orchards per village: one orchard treated and orchard untreated) scattered in the Borgou department (northern Benin) were monitored weekly with fly traps, and the fruit was sampled twice for larval infestation at the beginning and in the middle of May in both 2006 and 2007. The two main mango fruit fly pests are Ceratitis cosyra (Walker) and Bactrocera invadens Drew, Tsuruta & White, an invasive species that recently spread throughout West Africa. In both the 2006 and 2007 seasons, C. cosyra had the earliest peak of abundance, and the difference between treated and untreated orchards, in terms of mean number of flies trapped per week and per trap, was significant only in 2007. B. invadens populations quickly increased with the onset of the rains, from mid-May onward, with no significant difference between treated and untreated orchards. In 2006 and 2007, the larval infestation by B. invadens was significantly lower in plots treated with GF-120 than in untreated control plots. GF-120 provided an 81% reduction in the number of pupae per kilogram of fruit after weekly applications for 7 wk in 2006 and an 89% reduction after 10 wk of weekly applications in 2007. The possibility of integrating GF120 bait sprays in an integrated pest management package is discussed in relation to market requirements.

Sensitivity of Prostephanus truncatus (Coleoptera: Bostrichidae) Flight Activity to Environmental Variables in Benin, West Africa

Abstract Based on pheromone trap catches, a model of weekly Prostephanus truncatus (Horn) flight activity was generated for southern Benin. Using response surface regression, the following environmental variables were examined: number of rainy days per week, precipitation, minimum and maximum temperatures, minimum relative air humidity, and daylength. A time-variable, year, was included to account for the variance between years. From step-wise exclusion of variables with the lowest contribution to the model fit, a model was generated which included three environmental variables (daylength, minimum relative air humidity, and minimum temperature) that explained 55% of the total variance, and the yearly variable explaining 8%. The response surface regression analysis of P. truncatus flight activity revealed the following: (1) it was positively correlated with daylength when daily minimum temperature and relative air humidity were low, (2) it was positively associated with minimum relative air humidity when lower than 75%, (3) it was negatively associated with minimum temperature, (4) unexplained yearly variation was important for the predictive strength of the model, (5) interactions of environmental variables contributed substantially to the model fit, and (6) precipitation, both as mm rain and as number of rainy days, had little influence on P. truncatus flight activity. Independent data showed that the model predicted P. truncatus flight activity well elsewhere in southern Benin, whereas in central Benin new coefficients for the same environmental variables were needed to produce an adequate prediction. The model did not fit pheromone baited trap catches from northern Benin.

Spatial Analysis of Prostephanus truncatus (Bostrichidae: Coleoptera) Flight Activity Near Maize Stores and in Different Forest Types in southern Benin, West Africa

Abstract Weekly Prostephanus truncatus (Horn) flight activity, measured as the density of captured beetles in pheromone baited traps, was monitored for 76 consecutive weeks at 16 sites inside the Lama forest in southern Benin and at four sites in maize farmland just outside the forest. Prostephanus truncatus flight activity was consistently higher and the flight activity pattern significantly different near maize stores than at sites inside the forest. Although P. truncatus is known to infest girdled branches of Lannea nigritana (Sc. Elliot) Keay, the P. truncatus flight activity was comparatively low at forest sites where this tree species dominated. The main peak in P. truncatus flight activity occurred earlier in the eastern part of the forest compared with other forest parts. Ordination analysis showed that comparatively higher flight activity in the eastern part of the forest was positively associated with the presence of teak plantations (Tectona grandis L. F.) at trap sites. The spatial distribution of weekly P. truncatus trap catches were found to be significantly aggregated during a 21-wk period, which largely coincided with the early increase in P. truncatus flight activity in the eastern part of the forest. Based on this evidence, it was suggested that P. truncatus individuals disperse from the eastern part of the forest to other forest parts and to nearby agricultural areas, rather than, as has been previously suggested, from maize stores to the forest environment.

The effect of two biological control agents, the weevil Neochetina eichhorniae and the mirid Eccritotarsus catarinensis on water hyacinth, Eichhornia crassipes, grown in culture with water lettuce, Pistia stratiotes

We assessed the effect of two biological control agents, the mirid Eccritotarsus catarinensis (Carvalho) and the weevil Neochetina eichhorniae (Warner), singly or in combination, on the competitive ability of their host plant, water hyacinth, Eichhornia crassipes (Mart.) Solms-Laub., grown in a screen house, in competition with another aquatic plant (Pistia stratiotes L.). Water hyacinth plant growth characteristics measured included fresh weight, leaf and petiole lengths, number of inflorescences produced, and new shoots. Without herbivory, water hyacinth was 18 times more competitive than water lettuce (across all experimental combinations of initial plant densities), as estimated from fresh weights. Both insect species, singly or in combination, reduced water hyacinth plant growth characteristics. E. catarinensis alone was less damaging than the weevil and under normal conditions, i.e., floating water hyacinth, is not expected to increase control of water hyacinth beyond that of the weevil. When combined with the weevil, half the inoculum of weevils and half the inoculum of mirids produced the same growth reduction as the full inoculum of the weevil. Under conditions where the weevils are not effective because water hyacinths are seasonally rooted in mud, the mirid, which lives entirely on leaves, should become a useful additional biological control agent.

Survival of the mirid Eccritotarsus catarinensis as influenced by Neochetina eichhorniae and Neochetina bruchi feeding scars on leaves of water hyacinth Eichhornia crassipes

Water hyacinth (Eichhornia crassipes (Mart.) Solms-Laub.) remains a problem waterweed worldwide, for which biological control offers a sustainable solution. Under laboratory conditions, we investigated the interaction between two established weevil species Neochetina eichhorniae (Warner), Neochetina bruchi Hustache and the mirid Eccritotarsus catarinensis (Carvalho) which have been released together in several countries. Adult and immatures of E. catarinensis had high mortality on plants with high levels of old feeding scars from adult N. eichhorniae and N. bruchi and was significantly different at p < 0.05. In contrast, mirid survived well on plants with recent feeding scars from Neochetina spp. or on undamaged plants. Our results indicate that the mirid is compatible with the two weevil species for improving biological control of the weed.

Seasonal Abundance of Mango Fruit Flies (Diptera: Tephritidae) and Ecological Implications for Their Management in Mango and Cashew Orchards in Benin (Centre & North)

ABSTRACT We report the results of a large-scale (six orchards) and long-term (5-yr) study on seasonal population fluctuations of fruit flies (Diptera Tephritidae) in mango (2005–2009) and cashew (2007–2009) orchards in the Borgou Department, Benin. During the five consecutive years of mango fruit fly monitoring, 25 tephritid species were captured including three species of Bactrocera, 11 of Ceratitis, and 11 of Dacus, which is represented by 2,138,150 specimens in mango orchards. We observed significant differences in Bactrocera dorsalis (Hendel) counts between “high” and “low” mango production years from 2005 to 2008 but not in Ceratitis cosyra (Walker) counts. The native species, C. cosyra, the most abundant species during the dry season, peaked beginning of May, while the exotic species, B. dorsalis, the most abundant species during the rainy season, peaked in June. Preliminary results underlined the role of nine species of wild hosts and seven species of cultivated ones around mango orchards that played an important role in maintaining B. dorsalis in this Sudan zone all year round. The presence of C. cosyra stretched over 9 mo. During the first 14 wk of tephritid monitoring on cashew orchards situated near mango orchards, most flies (62%) were captured in traps positioned in cashew orchards, showing the strong interest of an early fly control on cashew before the mango season. According to these results, in the Sudan zone, effective and compatible control methods as proposed by the IPM package validated by the West African Fruit Fly Initiative project against mango fruit flies are proposed for a large regional tephritid control program in same zones ofWest Africa.

Scaling up tests on virulence of the cassava green mite fungal pathogen Neozygites tanajoae (Entomophthorales: Neozygitaceae) under controlled conditions: first observations at the population level.

Virulence of entomopathogens is often measured at the individual level using a single host individual or a group of host individuals. To what extent these virulence assessments reflect the impact of an entomopathogen on their host in the field remains largely untested, however. A methodology was developed to induce epizootics of the cassava green mite fungal pathogen Neozygites tanajoae under controlled conditions to evaluate population-level virulence of two (one Beninese and one Brazilian) isolates of the entomopathogen—which had shown similar individual-level virulence but different field impacts. In unrepeated separate experiments we inoculated mite-infested potted cassava plants with either 50 or 25 live mites (high and low inoculum) previously exposed to spores of N. tanajoae and monitored the development of fungal infections for each isolate under the same conditions. Both isolates caused mite infections and an associated decline in host mite populations relative to the control (without fungus) in all experiments, but prevalence of the fungus varied with isolate and increased with inoculum density. Peak infection levels were 90% for the Beninese isolate and 36% for the Brazilian isolate at high inoculum density, and respectively 17% and 25% at low inoculum density. We also measured dispersal from inoculated plants and found that spore dispersal increased with host infection levels, independent of host densities, whereas mite dispersal varied between isolates. These results demonstrate that epizootiology of N. tanajoae can be studied under controlled conditions and suggest that virulence tests at the population level may help to better predict performance of fungal isolates than individual-level tests.

Seasonal pattern in food gathering of the weaver ant Oecophylla longinoda (Hymenoptera: Formicidae) in mango orchards in Benin

Prey capture and food scavenging activities of Oecophylla longinoda were monitored through regular weekly samplings during two consecutive years (2009–2010) in a large mango orchard of the Borgou Department of Benin, West Africa, a main mango production area located in the Sudan agro-ecological zone. In both years, interspecific competition with other ants occurred mainly during the dry season (January to March) resulting in increased captures of Formicinae, Myrmicinae and Ponerinae. More prey was caught during the rainy season (end April to end October) than during the rest of the year, with Diptera and Coleoptera prey peaking in May and June, respectively, along with the mango season. As insect prey quickly decreased during November to December weaver ants increasingly collected seeds and plant debris. A total of 241 species of insects were captured including 61 species (25.3%) associated with mango and a few with cashew, among which 48 mango pest species (78.7% of species associated with mango tree). Only five species (2.1%) of beneficial insects were captured. It is concluded that the presence of O. longinoda colonies is beneficial to perennial tree cropping systems such as mango and cashew.

Intraspecific variability in agro-morphological traits of African yam bean Sphenostylis stenocarpa (Hochst ex. A. Rich) harms

Intraspecific variabilities in 40 accessions of African yam bean (AYB) were assessed through characterization of 48 agromorphological traits for two cropping seasons between June and December 2011 and 2012. Data were analyzed using descriptive statistics, analysis of variance (ANOVA), correlation analysis, principal component analysis, and cluster analysis (Semi-partial R squared method). The accessions showed significant differences (P ≤ 0.05, P ≤ 0.01, P ≤ 0.0001) in 16 reproductive traits. Accessions TSs 66 (144.50 days), TSs 51 (144.67 days) and TSs 154 (144.67 days) were identified as early maturing accessions. The first five principal component axes explained 69.7% of the total variation with PC1 and PC2 contributing 38.9% to the total variation. Correlation coefficients were high and significant for yield traits. A highly significant correlation (r = 0.99***) was observed between seed yield (kg ha-1) and weight of total pods per plant. Tubers were produced from 42.5% of the accessions. The accessions of AYB were meaningfully grouped into five clusters at the R-squared distance of 0.04 similarity index. Phenotypically, AYB 57 and TSs 123 were the most similar accessions with the closest distance of 0.0071. Four seed shapes were identified; oval (82.5%), globular/round (5%), oblong (10%), and rhomboid (2.5%). In order to improve the yield of AYB, the number of seeds per pod, number of pods per plant, weight of total seeds per pod, and weight of total seed per plant are important determinant factors. The genetic variabilities observed in the traits studied could be utilised for improvement of AYB.

Effect of planting date on incidence and damage by Sesamia calamistis (Lepidoptera: Noctuidae) in maize in southern Benin.

Stem and cob borers cause substantial damage to maize and affect the quality and economic value of maize in West Africa. Manipulation of planting dates is considered a possible mechanism for averting the overall impact of borers and their damage to the crop. Experiments were carried out in southern Benin to evaluate the effect of various planting dates on the incidence and damage to maize by Sesamia calamistis (Hampson). The trials were conducted at the Benin station of the International Institute of Tropical Agriculture (IITA) at Abomey-Calavi and at Sehoue, located 70 km north of the IITA, Benin station. The planting dates were: early planting (the day following the first rains), intermediate planting (2–3 weeks after the early planting) and late planting (4–5 weeks after the early planting). The experiments were carried out in the main and minor cropping seasons, respectively, during two successive years in 2003 and 2004. The variables measured included population density of S. calamistis, percentage of infested plants and cob damage. In the main cropping season, incidence of stemborers and percentage of infested plants were higher in the late planting than in the early planting and intermediate planting treatments. The manipulation of planting dates for the control of S. calamistis during the minor maize growing season is not recommended.