Agbéko Kodjo Tounou

Post-harvest insect infestation in maize grain stored in woven polypropylene and in hermetic bags

Maize was artificially infested with either 10 or 25 individual Prostephanus truncatus (Horn) and Sitophilus zeamais (Motschulsky) or a mixture of both, and stored in a hermetic grain bag (HGB) or a woven polypropylene bag (WPB) for 150 days. Population growth of P. truncatus and S. zeamais during storage was low in HGB, while in WPB, the insect population increased significantly with storage duration. Mortality rate during storage was significantly higher in HGB than in WPB. After 60 days of storage, the average mortality rate of 99.50% was observed in HGB infested with 25 P. truncatus, and 100% for S. zeamais at the same infestation density after 90 days of storage. Grain losses were significantly lower in HGB compared with WPB. Less than 0.5 and 6.0% losses were obtained, respectively, for S. zeamais and P. truncatus in HGB infested with 25 individual insects after 150 days of storage, whereas losses of 19.2% (infestation with S. zeamais) and 27.1% (infestation with P. truncatus) were observed in WPB. HGB seems to be resistant to the perforation of S. zeamais, but not to P. truncatus. The moisture content of maize grains stored in HGB remained practically the same during storage, compared with the levels in WPB, which reduced with storage time. WPB could be used for maize storage, protecting it against insect infestation without the need for insecticide use.

Chemical Composition and Insecticidal Activity of Ocimum canum Essential Oil Against Coffee Berry Borer, Hypothenemus hampei (Ferrari) (Coleoptera: Scolytidae)

Abstract The chemical compositions of the essential oils of Ocimum canum Sims (Lamiaceae) areal part cultivated in Togo were investigated by GC-MS and tested for possible insecticidal activity against the coffee berry borer, Hypothenemus hampei (Ferrari) (Coleoptera: Scolytinae) under laboratory. Eighteen constituents (98.5 % of the total oil) were identified in the volatile oil of O. canum leaf. The main constituents found in the oil were terpineol-4 (34.7 %), linalool (22.7 %), λ-terpinene (7.3 %), trans-thujan-4-ol (5.9 %), trans-α-bergamotene (4.9 %) and caryophyllene (4.6 %). Other components were also identified by at minor concentrations ranging from 0.12 % (Thymol) to 2.7 % (Limonene). In the insecticidal activity test, crude essential oil of O. canum emulsions of exhibited adulticidal activity against coffee berry borer and response was being dose-related. The LD50 were 320 ppm for O. canum essential oil and 450 ppm for endosulfan and the conventional insecticide used as standard, respectively. The results indicate that the O. canum essential oil has a potential insecticidal activity and can be used as active ingredient in natural and sustainable pesticide within an Integrated Pest Management approach to combat the coffee berry borer.

Interaction between the aphid parasitoid Lysiphlebus testaceipes (Hymenoptera: Aphidiidae) and its hyperparasitoid Syrphophagus africanus (Hymenoptera: Encyrtidae)

The interactions between the cowpea aphid Aphis craccivora Koch, its parasitoid Lysiphlebus testaceipes Cresson and hyperparasitoid Syrphophagus africanus Gahan were assessed in the laboratory. Host age preference for hyperparasitism was evaluated using parasitized aphids of different ages (i.e. 1, 2, 3, 4, 5 and 6 days old and mixed ages). We studied the influence of the hyperparasitoid on the parasitism efficiency of L. testaceipes, the effect of host age on some biological parameters of S. africanus, and its hyperparasitism based on aggregated or isolated mummies. The presence of S. africanus significantly affected aphid parasitism by L. testaceipes (21.2 ± 3.6 vs 36.6 ± 4.5%). Except for 1-day-old hosts, S. africanus successfully parasitized hosts of all tested ages, with preference for newly formed mummies (39.16 ± 3.31% parasitism in 5-day-old hosts). The development time of immature stages of the S. africanus progeny was significantly affected by host age. The sex ratio of the hyperparasitoid progeny was largely female biased and did not vary with host age. Syrphophagus africanus females from live parasitized aphids produced more offspring (36.55 ± 6.28 vs 25.00 ± 7.16) and lived longer (21.09 ± 1.57 vs 10.88 ± 2.31 days) than those from mummy hosts. Hyperparasitism rates were higher on aggregated mummies than on dispersed ones (36.00 ± 2.86 vs 20.66 ± 4.00%).

Etude comparée de l’efficacité de la cyperméthrine et deux bioinsecticides, Beauveria bassiana et suneem contre l’altise du gombo, Podagrica spp (Coleoptera: Chrysomelidae)

Parmi les ravageurs du gombo, Abelmoschus Spp L., les altises, Podagrica Spp (Coleoptera: Chrysomelidae), causent d’importants dommages a la culture. Les fortes infestations de l’insecte reduisent les activites photosynthetiques de la plante, entrainant des pertes elevees de rendement. La presente etude vise a comparer l’effet de deux bioinsecticides, Suneem 1% EC, 10 g/l d’azadirachine (20%), Beauveria bassiana (1 x1011 spores/ha) et le cypermethrine 50 EC (1 l / ha), un insecticide de synthese, pour le controle de Podagrica Spp, en conditions de champ. Deux applications des differentes formulations ont ete faites a intervalle de 6 jours sur la partie aerienne des plantes. Les resultats ont montre que la cypermethrine a cause la plus forte reduction de la densite de population des altises (89,56 ± 0,76), suivi de Suneem (81,24 ± 2,40) et du B. bassiana (64,90 ± 3,07). De meme le pourcentage des feuilles attaquees et le pourcentage de surface foliaire endommagee par l’insecte ont ete significativement affectes par les traitements. Il ressort de cette etude que B. Bassiana et le Suneem, peuvent etre utilises pour lutter efficacement contre les populations d’altises de gombo, Podagrica Spp en condition de champ. Mots cles : Bioinsecticide, champignon entomopathogene, altise du gombo, reduction de la densite.

Influence of Rearing Substrates and Nontarget Hosts on the Bionomics of the Tachinid Parasitoid Nemorilla maculosa (Diptera: Tachinidae)

Abstract The tachinid Nemorilla maculosa Meigen (Diptera: Tachinidae) was introduced from Taiwan to Benin for evaluating its potential as a biocontrol candidate against the cowpea pest Maruca vitrata (Fabricius) (Lepidoptera: Crambidae). To optimize its rearing, we assessed the influence of M. vitrata larval age and rearing substrate—cowpea germinating grains and peabush leaves—on its life table parameters, while its host specificity was investigated with regard to nontarget effects. Parasitism rates were higher when older larvae (10- and 14-d old) were offered to females of N. maculosa compared to the younger (2-, 4-, and 6-d old) host larvae. Regardless of the rearing substrate, development time was longer for females than males, and females lived longer than males irrespective of the age of the host. Sex ratio did not vary significantly with host ages or rearing substrate. The average number of eggs laid by a female reared from M. vitrata larvae feeding on cowpea germinating grains or peabush leaves was 94.2 ± 4.38 and 71.9 ± 1.70 eggs, respectively. The host suitability of N. maculosa was assessed by testing four nontarget Lepidoptera species: Spodoptera littoralis Boisduval (Lepidoptera: Noctuidae), Sesamia calamistis Hampson (Lepidoptera: Noctuidae), Corcyra cephalonica (Stainton) (Lepidoptera: Pyralidae), and Eldana saccharina Walker (Lepidoptera: Pyralidae). Larvae of S. littoralis and C. cephalonica were successfully parasitized while N. maculosa did not develop in the larvae of E. saccharina and S. calamistis although they were parasitized. Despite the potential of N. maculosa as a biological control agent against the pod borer M. vitrata, more detailed nontarget studies, extending to other native Crambidae species, are needed before making decisions on field releases.

The parasitic fly Nemorilla maculosa exploits host-plant volatiles to locate the legume pod borer, Maruca vitrata

Nemorilla maculosa Meigen (Diptera: Tachinidae) is a solitary endoparasitoid of the legume pod borer, Maruca vitrata Fabricius (Lepidoptera: Crambidae), a key pest of cowpea, Vigna unguiculata (L.) Walp. (Fabaceae) in Africa. A colony of N. maculosa, introduced for experimental purposes from Taiwan to the laboratories of the International Institute of Tropical Agriculture (IITA) in Benin, was used for our studies. Olfactory reponses of N. maculosa to leaves of infested or uninfested cowpea and yellow peabush, Sesbania cannabina (Retz.) Pers. (Fabaceae), and to M. vitrata larvae were evaluated in a four‐arm olfactometer. For all combinations of odor sources, responses between naïve and oviposition‐experienced female flies did not differ. Nemorilla maculosa females were attracted by odors from uninfested leaves of yellow peabush and flowers of cowpea when compared with clean air, and they were attracted to plants damaged by M. vitrata with larvae removed. However, the female fly did not discriminate between odors from infested and uninfested plants. The parasitic fly N. maculosa proved well able to use volatile compounds from various host plants (peabush and cowpea) to locate its host, with a more pronounced attraction by the combination of host larvae and infested host plant parts. These findings are discussed in light of the prospective use of N. maculosa as a biological control agent against the legume pod borer.