Effectiveness of binary combinations of Plectranthus glandulosus leaf powder and Hymenocardia acida wood ash against Sitophilus zeamais (Coleoptera: Curculionidae)

Jean Wini Goudoungou,Elias Nchiwan Nukenine,Christopher Suh,Tiburce Gangué,Dieudonné Ndjonka

doi:10.1186/s40066-018-0179-z

Abstract

BackgroundBotanicals are generally assumed to be more biodegradable, leading to less environmental problems. Combination of botanicals could enhance biological activity against insect pests. Hence, the amount of botanical used for the control of stored grain pests may be minimised. In this study, the bioassay was carried out on Sitophilus zeamais to assess the effectiveness of binary combinations of Hymenocardia acida wood ash and Plectranthus glandulosus leaf powder. The quantities of mixed products were added to maize grains to constitute the contents of 5, 10, 20 and 40 g/kg. Then, the bioassays on toxicity within 1, 3, 7 and 14 days exposure, progeny production, population increase, grain damage and germination ability of protected grains were carried out.ResultsThe major compounds (pinene, α-pinene, α-terpineol, thymol, β-myrcene and 3-carene) of P. glandulosus leaf powder were monoterpenes. The major non-monoterpenic constituent was an oxygenated sesquiterpene, β caryophyllene oxide. The chemical analysis of H. acida ash showed that calcium (5800 mg/kg) and phosphorus (2782 mg/kg) recorded higher content than the other minerals. Plectranthus glandulosus leaf powder, H. acida wood ash and their binary combinations significantly induced mortality of S. zeamais adult (P < 0.0001). The higher mortality rate was achieved by the highest content within 14 days of exposure. The combinations of P. glandulosus leaf powder with H. acida at different proportions produced different interactions. The mixture of 75% P. glandulosus and 25% H. acida produced synergistic effect, whereas the mixture of 50:50 had antagonistic effect in weevil mortality. The three combinations of H. acida and P. glandulosus significantly reduced the production of the progeny compared to the control. From the application of 5 g/kg (lowest content), the number of emerging adults was highly reduced. The combination 25PG75HA revealed to be more effective than the two other against F1 production. The grain damage and population growth were significantly reduced. In general, the non-infested maize grain had a good germination rate than the infested ones. The treatment did not have negative effect on seed germination.ConclusionsFrom our results, the two powders and their binary combinations could be used to reduce grain infestation by insect while taking into account the proportions of insecticidal powders implied in the combination.

Highlights

Botanicals are generally assumed to be more biodegradable, leading to less environmental problems
Chemical analysis Plectranthus glandulosus leaf powder The volatile constituents of the essential oils from P. glandulosus leaf powder were identified by their retention indices and mass spectra in comparison with those of standard synthetic compounds
The additive effect was observed; the effect of two materials is equal to the sum of each component given alone (1 + 3 = 4), which was observed in the present study by the combination 25PG75HA (25% P. glandulosus leaf powder and 75% H. acida wood ash) within 14 days of exposure

Summary

Introduction

Botanicals are generally assumed to be more biodegradable, leading to less environmental problems. Cereals constitute the group of most consumed grain in sub-Saharan African, especially in Sahelian zones. In these zones, cereals are very interesting according to its conservation ability. The conserved and protected seeds permit availability of seeds (food) throughout the year, thereby contributing to food security. Cereals such as sorghum, millets, wheat, maize and rice are major staple foods of most population. The production of maize is done in the short period of the year, whereas its commercialisation and consumption are done all year round This makes imperative the storage and the protection of this grain. The insufficiencies of different storage methods in developing countries have not stopped to cause grain losses and this in unacceptable proportions [3]

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