Mussidia Nigrivenella Research Articles

The effect of leguminous cover crops and cowpea planted as border rows on maize ear borers with special reference to Mussidia nigrivenella Ragonot (Lepidoptera: Pyralidae)

In southern Benin, the use of cover crops to improve and maintain soil fertility is on the increase. The present study investigated the effect of two leguminous cover crops, Canavalia ensiformis (L.) DC and Sesbania rostrata Brem. & Oberm., planted at different dates before maize (Zea mays (L.)), and cowpea (Vigna unguiculata L.) planted as border rows on infestations of maize by the pyralid Mussidia nigrivenella Ragonot and of other cob-boring lepidopteran pests. In both trials, M. nigrivenella densities at harvest tended to be higher in the maize alone than the legume treatments, but the effect depended on the timing of planting of the cover crop in relation to that of maize. There were no discernible trends for other borers such as the noctuid Sesamia calamistis Hampson, the pyralid Eldana saccharina Walker, and the tortricid Thaumatotibia leucotreta Meyrick. Furthermore, M. nigrivenella pest loads were considerably higher on C. ensiformis than maize, indicating that the presence of alternative host plant species in the vicinity of maize fields did not increase M. nigrivenella attack on maize. Though in some of the legume treatments, grain damage and grain losses were higher than in the maize alone plots, per area yields did not vary significantly.

Dietary and Thermo-Hygrometric Requirements to RearMussidia fioriiCecconi & de Joannis (Lepidoptera: Pyralidae) Under Laboratory Conditions

Several Mussidia species occur in West and East Africa, but only the ear-borer, Mussidia nigrivenella Ragonot (Lepidoptera: Pyralidae), has attained economic pest status in West Africa. During recent surveys in Kenya several parasitoid species were recovered from Mussidia species, including the egg parasitoid, Trichogrammatoidea sp. nr lutea Girault (Hymenoptera: Trichogrammatoidea). This parasitoid species is considered a potential biocontrol agent for M. nigrivenella in West Africa and development of a successful rearing system for its host, M. fiorri, will enable the mass production of this natural enemy species. The suitability of five artificial diets for the development of M. fiorii as well as optimum rearing conditions were evaluated in the laboratory. The effect of temperature and humidity on the development of M. fiorii was also studied. Mussidia fiorii successfully developed on maize leaf-, maize seed- and Canavalia ensiformes seed-based diets. The lower developmental thresholds for the egg, lar...

Performance of Trichogrammatoidea sp. nr lutea Girault (Hymenoptera: Trichogrammatidae) collected from Mussidia spp. in Kenya on eggs of six lepidopteran hosts

Abstract Mussidia nigrivenella Ragonot (Lepidoptera: Pyralidae), an important pest of maize ears in West Africa, has never been reported to attack crops in East and southern Africa (ESA), though it was found on various wild host plants in these regions. It was suggested that in ESA M. nigrivenella might be under natural control. In Kenya, exploration for natural enemies associated with Mussidia spp. yielded several parasitoids including a trichogrammatid egg parasitoid, Trichogrammatoidea sp. nr lutea Girault. The ability of T. sp. nr lutea to attack the eggs of several lepidopteran species found in Kenya was studied. The lepidopterans included the noctuids Busseola fusca (Fuller) and Sesamia calamistis (Hampson), the pyralids Eldana saccharina Walker, Mussidia fiorii Cecconi and de Joannis and Mussidia‘madagascariensis’, and the crambid Chilo partellus (Swinhoe). The former three species also infest cereals in West Africa. Trichogrammatoidea sp. nr lutea successfully attacked and developed in eggs of all six species indicating its potential to exploit other lepidopteran pests of maize in West Africa. Busseola fusca and S. calamistis were the most suitable hosts and had the largest number of eggs parasitized and progeny per female wasp where E. saccharina and C. partellus were the poorest hosts. The host species used to rear the parasitoid and the age of egg also significantly affected the total number of host eggs parasitized by the parasitoid. It was concluded that the ability of T. sp. nr lutea to exploit lepidopterans that are also pests of maize in West Africa may enhance biological control of M. nigrivenella and it should be considered for translocation to that area from Kenya.

The importance of Mussidia nigrivenella Ragonot (Lepidoptera: Pyralidae) as a post-harvest pest in different storage structures in Benin

In West Africa, the most damaging lepidopteran pest of maize ears is the pyralid Mussidia nigrivenella. Although it is mostly described as a field pest, it can be found feeding on maize stored for up to 4 months. A survey was conducted in Benin in 2006 to assess M. nigrivenella infestations in different maize storage systems in the Southern (SGS) and Northern Guinea Savanna (NGS). In SGS and NGS the percentage of infested stores decreased from 86.7% to 26.7% and from 51.4% to 14.3%, respectively, during the first 28 weeks of storage. During the same time, mean numbers of M. nigrivenella per cob decreased from 0.36 to 0.04 across both zones. All larval stages, but mostly 3rd–5th instars, were frequently found even after more than 12 weeks, indicating that M. nigrivenella may have reproduced in storage, although reinfestation or delayed development could also explain this observation. The highest M. nigrivenella incidences of 16.8% and 14.4% were found in the “Ava” and crib stores, respectively. Infestations were highest in “Ava” and lowest in maize grain stored in polyethylene bags or in mud silos. In a laboratory experiment, the presence of post-harvest beetles negatively affected the bionomics of M. nigrivenella, indicating strong interspecific competition.

Effects of plant extracts and oil emulsions on the maize cob borer Mussidia nigrivenella (Lepidoptera: Pyralidae) in laboratory and field experiments

Aqueous extracts of Tephrosia vogelii and Hyptis suaveolens, and of oils of Azadirachta indica and Jatropha curcas, as well as the pesticide Furadan 5G were evaluated for their insecticidal activity against the maize cob borer Mussidia nigrivenella Ragonot in laboratory and field experiments. In general, treated plants had a strong deterrent effect on ovipositing M. nigrivenella. The oviposition deterrence index was highest with neem oil at both concentrations, J. curcas at 5% and H. suaveolens at 20%. In addition, neem and Jatropha oils adversely affected egg hatch; it decreased with an increase in concentrations of oil emulsions and varied between 3 and 25.5% for neem and 6 and 16% for J. curcas. The lethal concentration 50 values calculated were 1.3 and 0.8%, respectively, for neem and J. curcas. By contrast, larval survival was not affected by the oil treatments. In the field, Furadan, neem and J. curcas oils significantly reduced the number of M. nigrivenella larvae by 16–49.2%, while aqueous extracts of T. vogelii and H. suaveolens were similar to the emulsified water control. The treatments did not significantly influence cob weight, and only neem oil at both concentrations and Furadan significantly reduced cob damage and consequently grain losses. These results showed that oil emulsions of A. indica and J. curcas oils act not only as an oviposition deterrent but also as ovicides. The prospects for possible inclusion of botanicals into integrated M. nigrivenella control in maize cropping systems are discussed.

Physiological suitability of six West African gramineous borers (Lepidoptera: Noctuidae, Pyralidae) for development of Cotesia species complex (Hymenoptera: Braconidae)

Three gregarious, endoparasitic braconids, a Kenyan strain of Cotesia sesamiae, and the exotic Cotesia flavipes and Cotesia chilonis were imported into Benin as candidates for biological control of stem- and cob borers of maize and stemborers of millet. Host acceptability and host suitability of six gramineous borers occurring in western Africa, the noctuids Sesamia calamistis, Sesamia poephaga, Busseola fusca, the crambid Coniesta ignefusalis, and the pyralids Eldana saccharina and Mussidia nigrivenella, to these parasitoids were evaluated to test the hypothesis that new associations were superior over old association parasitoid-host relationships. All hosts were accepted by all Cotesia spp., except M. nigrivenella, which was not attacked by C. chilonis. Parasitoid progeny developed successfully in S. calamistis, S. poephaga and C. ignefusalis. S. calamistis was the most suitable host in terms of duration of developmental time, brood size and mortality of parasitoid progeny. It was concluded that because of its host specificity, the old association parasitoid C. sesamiae would have the highest chance of establishment in cereal systems in West Africa.

Host plants and species diversity of Mussidia (Lepidoptera: Pyralidae) in Kenya

Mussidia nigrivenella (Lepidoptera: Pyralidae), an important pest of maize, cotton and Phaseolus bean in western Africa, has never been described as a crop pest from Eastern and southern Africa (ESA), although it was reported in the wild. Generally, little is known about the host plant range and the diversity of Mussidia spp. in ESA. Thus, surveys were carried out in Kenya between 2005 and 2007 to assess the species diversity and host plants of Mussidia. Eight plant species were found to host two Mussidia spp. and six morphospecies, which occur sympatrically in the coastal region. Only one Mussidia sp. was found attacking one host plant in the mid-altitudes. The spatial distribution of M. nr. nigrivenella, M. ‘madagascariensis’ and M. fiorii was studied. M. nr. nigrivenella and M. ‘madagascariensis’ larvae were aggregated on Canavalia cathartica and Strychnos madagascariensis, respectively, while the distribution of M. fiorii adults on Kigelia africana was regular. Sampling plans were developed for three Mussidia spp. on their respective host plants, allowing estimation of pest densities. The occurrence of M. nigrivenella in ESA could not be determined with absolute certainty.

Parasitoids Associated with Mussidia spp. (Lepidoptera: Pyralidae) in Kenya

The pyralid Mussidia nigrivenella, a pest of cotton, maize and Phaseolus bean in West Africa, has never been reported as a crop pest in East and Southern Africa, although reportedly it exists in the wild. It is hypothesized that the difference in pest status of M. nigrivenella between western and eastern Africa was either due to differences in natural enemy compositions or that there exist several populations and/or species of Mussidia, which vary in their host plant range. Thus, a catalogue of parasitoids of Mussidia spp. was established through surveys in mid-altitude and coastal Kenya, between 2006 and 2007. Mussidia spp. eggs, larvae and pupae were collected from fruits of plants known to host Mussidia spp. and were examined for parasitoid-related mortality. The trichogrammatid Trichogrammatoidea sp. nr. lutea was obtained from eggs of Mussidia fiorii. A braconid egg-larval parasitoid, Phanerotoma sp., was reared from the larvae of unknown species of Mussidia (which we are referring to as Mussidia “madagascariensis”, Mussidia “quanzensis”) and M. fiorii, while the bethylid Goniozus sp. and the braconid Apanteles sp. were obtained from Mussidia nr. nigrivenella. Moreover, the ichneumonid larval parasitoid Syzeuctus sp. was obtained from M. fiorii, while the tachinid Leskia sp. was obtained from Mussidia “madagascariensis”. Overall, mortality caused by parasitoids was negligible; hence they were not considered key mortality factors in the population dynamics of the Mussidia spp. in Kenya.

Host suitability and thermal requirements of Lathromeris ovicida Risbec (Hymenoptera: Trichogrammatidae), an egg parasitoid of cereal stemborers in Africa

Factors affecting the bionomics of the trichogrammatid egg parasitoid Lathromeris ovicida and its association with the two sympatric scelionid egg parasitoids Telenomus busseolae and Telenomus isis were studied in the laboratory. The potential host species employed were the noctuids Sesamia calamistis and Sesamia botanephaga , and the pyralids Eldana saccharina and Mussidia nigrivenella . Using eggs of S. calamistis Hampson as hosts, the lower and upper thresholds for development were estimated at 14.8 and 34 °C, respectively. The percent parasitism, total progeny, and sex ratio decreased gradually from 42.0 to 10.2, from 56.4 to 10.8, and from 0.74 to 0.61, respectively, with host age. The intrinsic rate of increase and female fecundity was highest on the two noctuids, followed by E. saccharina and M. nigrivenella . Lathromeris ovicida preferentially attacked eggs already parasitised by either Telenomus busseolae or Telenomus isis . Thus, L. ovicida is probably a facultative hyperparasitoid.

Multi-trophic level interactions in a cassava-maize mixed cropping system in the humid tropics of West Africa.

Multi-trophic level interactions in a mixed crop, involving cassava and maize, were studied in derived-savanna in Benin, West Africa. Two trials were planted, one during the short rainy season two months before onset of the dry season and one during the long rainy season in spring. Key pests under study on maize were the noctuid Sesamia calamistis Hampson and the pyralids Eldana saccharina Walker and Mussidia nigrivenella Ragonot, and on cassava, the exotic mealybug, Phenacoccus manihoti Matile-Ferrero and its encyrtid parasitoid Apoanagyrus lopezi De Santis. Both crops received insecticide treatments to assess the crop loss by a pest species. On maize, intercropping with cassava reduced egg and immature numbers of S. calamistis by 67 and 83%, respectively, as a result of reduced host finding by the ovipositing adult moth and of higher egg parasitism by Telenomus spp. Both trials showed similar effects on maize yields: on insecticide-treated maize, intercropping with cassava reduced maize yields by 9-16%, while on untreated maize the net effect of reduced pest density and increased plant competition resulted in zero yield differences; yield losses were lower in inter- compared to monocropped maize. For cassava, cropping system had no effect on parasitism by A. lopezi. Yield differences between mono- and intercropped cassava depended on time of harvest: they were large at the beginning and zero at final harvest. Land equivalent ratios were mostly > 1.5 indicating that a maize/cassava mixed crop, protected or unprotected, considerably increased the productivity per unit area of land.

Host suitability and thermal requirements of Lathromeris ovicida Risbec (Hymenoptera: Trichogrammatidae), an egg parasitoid of cereal stemborers in Africa

Abstract Factors affecting the bionomics of the trichogrammatid egg parasitoid Lathromeris ovicida and its association with the two sympatric scelionid egg parasitoids Telenomus busseolae and Telenomus isis were studied in the laboratory. The potential host species employed were the noctuids Sesamia calamistis and Sesamia botanephaga, and the pyralids Eldana saccharina and Mussidia nigrivenella. Using eggs of S. calamistis Hampson as hosts, the lower and upper thresholds for development were estimated at 14.8 and 34 °C, respectively. The percent parasitism, total progeny, and sex ratio decreased gradually from 42.0 to 10.2, from 56.4 to 10.8, and from 0.74 to 0.61, respectively, with host age. The intrinsic rate of increase and female fecundity was highest on the two noctuids, followed by E. saccharina and M. nigrivenella. Lathromeris ovicida preferentially attacked eggs already parasitised by either Telenomus busseolae or Telenomus isis. Thus, L. ovicida is probably a facultative hyperparasitoid.

The effect of Fusarium verticillioides on oviposition behaviour and bionomics of lepidopteran and coleopteran pests attacking the stem and cobs of maize in West Africa

Abstract The effect of Fusarium verticillioides Sacc. (Nirenberg) in maize stem and grain on the oviposition behaviour and bionomics of lepidopteran and coleopteran pests in West Africa was studied in olfactometer, greenhouse, and field trials in Benin. In a choice experiment, the pyralid Eldana saccharina (Walker) laid on average 31.9 eggs on inoculated maize stems vs. 9.2 and 7.8 on stems from plants, grown from hot‐water or fungicide treated seeds, respectively. For the pyralid Mussidia nigrivenella (Ragonot) the values were 42.1 in the inoculation and 7.8 eggs in the fungicide treatment. The survival of E. saccharina larvae was significantly higher from the inoculation than the hot‐water or fungicide treatments. Fecundity in the three treatments was 494, 307, and 268 eggs per female, respectively. In an olfactometer experiment, no significant differences were found in the time spent by the curculionid Sitophilus zeamais Motschulsky between the odor field with Fusarium‐infected grain and with uninfected grain, but both were significantly different from the controls. Significant differences were obtained for the nitidulid Carpophilus dimidiatus (Fabricius) with 50.5 and 35.8%, respectively, of the time spent in the Fusarium‐infected and non‐infected odor field. For both species, no differences were found between sexes. For S. zeamais, development time was significantly higher when reared on infected (37.2 days) than on non‐infected grain (34.4 days), whereas fecundity, expressed as number of progenies during the first 4 weeks, was lower on the inoculated grain (11 vs. 16 offspring per female). For C. dimidiatus the situation was the reverse: development time was shorter and fecundity was higher on infected grain (32.4 vs. 34.4 days, and 18 vs. 13 offspring per female, respectively). It was concluded that the higher pest densities found in the stem and ear of field grown maize was due to a higher attraction to and higher immature survival and adult fecundity on F. verticillioides infected plants.

The role of wild grasses in the management of lepidopterous stem-borers on maize in the humid tropics of western Africa

Sites in the humid forest of Cameroon and the derived savanna of Benin were selected to evaluate the effect of planting border rows of wild host plants on lepidopterous stem-borer infestations and on maize yield. Grass species were chosen that in surveys and greenhouse trials were highly attractive to ovipositing female moths but with offspring mortality of close to 100%, thus acting as trap plants. In Cameroon, elephant grass Pennisetum purpureum Moench significantly lowered infestations of Busseola fusca (Fuller), Sesamia calamistis Hampson and Eldana saccharina Walker and increased yields of maize though the differences were not significant during all three cropping seasons. In 1998 in Benin, the only grass tested, Pennisetum polystachion L., significantly increased parasitism of mainly S. calamistis eggs by Telenomus spp. and larvae by Cotesia sesamiae Cameron and reduced numbers of the cob-borer Mussidia nigrivenella Ragonot. In 1999, three grass species; P. polystachion, Sorghum arundinaceum (Desv.) Stapf and Panicum maximum Jacq. were tested. Panicum maximum was the most efficient species for suppressing S. calamistis and M. nigrivenella infestations and enhancing egg and larval parasitism. In the Benin trials, with the exception of M. nigrivenella damage to cobs, the grass species tested had no beneficial effect on yield because pest densities were too low and also rodent damage to maize was enhanced with grasses in the vicinity of the crop. By contrast, stand losses due to Fusarium verticillioides Sacc. (Nirenberg), were significantly reduced by border rows of grasses.

Yield of Maize in Relation to Natural Field Infestations and Damage by Lepidopteran Borers in the Forest and Forest/Savanna Transition Zones of Cameroon

The effect of infestation of lepidopteran borers on yield of maize was assessed at three locations in the forest and forest/savanna transition zones of Cameroon, during the first and second season of 1992. Maize was treated once or twice with the systemic carbofuran at different developmental stages. The species encountered were the stem-boring noctuids Busseola fusca and Sesamia calamistis, which oviposit on and attack pre-tasseling stages of maize; the stem-boring pyralid Eldana saccharina, which attacks plants at and after tasseling; and two ear borers, namely the pyralid Mussidia nigrivenella and the tortricid Cryptophlebia leucotreta. Generally, carbofuran reduced infestations by B. frisca and S. calamistis but had little or no effect on species attacking the plant’s later stages. Thus early treatments with granules into the whorl were more efficient than late treatments as a side dressing, and a second late treatment had little effect. During the first season, late-attacking species were predominant and grain yield losses of 172–44 % were found in one location only. During the second season, species attacking young plants (mainly B. fusca) became predominant in all three locations and yield losses of 30 to 41 % were found in two of the three locations. The percentage of ears with damage was especially high during the second season. As green maize is an important source of cash income in the area and damaged ears cannot be sold, the economic loss was likely considerable.

The Effect of Endophytic Fusarium verticillioides on Infestation of Two Maize Varieties by Lepidopterous Stemborers and Coleopteran Grain Feeders

ABSTRACT A series of experiments were conducted to test the effect of the presence of Fusarium verticillioides in the maize plant on subsequent infestation by coleopteran and lepidopteran pests. The effect of percent internodes 1 to 5 infected with F. verticillioides, time after planting, and maize variety on attacks of stem and ears by lepidopterous and coleopteran pests was assessed in field experiments in early and late season 1998 and early season 1999 in Benin Republic. Artificial inoculation of the first internode with fungal-treated toothpicks was compared with a hot-water-fungicide seed treatment and a control. In 1998, two varieties that differed in husk tightness, the improved DMRLSR-W and the local Gbogbe, were used. Percentage of node 1 to 5 and plants infected was highest with the inoculation treatment but tended to be similar in the seed treatment and the control. The infection rate tended to increase with time and, within sampling date, decreased with node level. Ear infection was strongly correlated with percent infected nodes, indicating that F. verticillioides in the stem predisposed kernel infection. F. verticillioides incidence was higher in Gbogbe than in DMRLSR-W. Stem and ear infestations by the pyralid Eldana saccharina, the major pest in the area, tended to be highest in inoculation and lowest in the protection treatment. The same trends were found for the pyralid Chilo spp., the tortricid Cryptophlebia leucotreta, and beetles pooled across species. Significant positive correlations were found between ear/stem F. verticillioides infection and E. saccharina, Cryptophlebia leucotreta, Mussidia nigrivenella, and the noctuid Sesamia calamistis, but the latter three pest species were only significantly correlated with fungal infection of the upper nodes of the plant. Similar to disease incidence, E. saccharina numbers in stem and ear were higher in Gbogbe than DMRLSR-W in late 1998, whereas for the pyralid ear feeder M. nigrivenella, it was reversed. It was suggested that some lepidopterous and coleopteran pests are attracted by and survive longer (or have lower mortality) on plants infected with F. verticillioides.

Spatial dynamics of lepidopterous pests on Zea mays (L.) and Pennisetum purpureum (Moench) in the forest zone of Cameroon and their implications for sampling schemes

The most common lepidopterous borers attacking maize and/or the wild host Pennisetum purpureum in the forest zone of Cameroon are the noctuids Busseola fusca (Fuller), Sesamia calamistis (Hampson) and Poeonoma serrata (Hampson), the pyralids Eldana saccharina (Walker) and Mussidia nigrivenella (Ragonot), and Cryptophlebia leucotreta (Tortricidae). The within‐plant distribution on maize and elephant grass was studied for the predominant species B. fusca, and on maize only for E. saccharina to determine the basic sampling unit. On both plant species, B. fusca showed a strong oviposition preference for young plant parts. By contrast, E. saccharina larvae and pupae on maize were only found on older plant parts indicating that it does not oviposit on young plants. No part of the plant strata appeared to be a stable sampling unit and it is recommended to carry out whole plant or whole tiller sampling for maize and grass, respectively. For the development of sampling plans, dispersion was described for all species using Taylor’s power law and a non‐linear model which gives the relationship between the proportion of infested plants [P(I)] and mean density (m). Busseola fusca egg batches as well as diapausing larvae and pupae on maize showed a random distribution whereas all the other cases were aggregated, with B. fusca egg batches on elephant grass exhibiting the lowest and M. nigrivenella on maize the highest aggregation. Optimal sample size/mean density curves were developed for groups of insects with low and high aggregation.

Distribution, relative importance and effect of lepidopterous borers on maize yields in the forest zone and mid-altitude of Cameroon.

Geographic distribution, relative importance, and effect of lepidopterous stem and ear borers on maize, Zea mays L., were studied in the humid forest and the mid-altitude zones of Cameroon from 1994 to 1997. Six villages were chosen in the forest zone and grouped into three blocks representing gradients in human population density. A single block with three villages was chosen in the mid-altitude. Farmers' maize fields were surveyed during the vegetative growth phase for Busseola fusca (Fuller) egg batches, and at harvest for number of larvae and pupae by species, plant damage, and ear weight. There was no significant block effect for any of the variables measured, and most of the overall variance (72-99%) was attributed to within-field variability. In the forest zone, the noctuid B. fusca and the pyralid Eldana saccharina (Walker) accounted for >80% of all species in almost all locations, followed by the pyralid Mussidia nigrivenella (Ragonot) and the tortricid Cryptophlebia leucotreta (Meyrick). The noctuid Sesamia calamistis (Hampson) was found in almost all locations during the first season but disappeared in most locations in the second season. B. fusco egg infestation was significantly higher during the second compared with the first season, whereas larval and pupal densities were much higher during the first season. E. saccharina was the predominant species during the second season, when densities increased fourfold. In the mid-altitude, B. fusca was the predominant species. No significant differences in pest densities, plant damage, and ear weight were found between years. Results of stepwise regression of stem and ear damage on pest densities verified the relative importance of the individual species. In the forest zone, ear and stem damage significantly reduced ear weight, whereas in the mid-altitude only stem tunneling was significant.

Natural enemies of lepidopterous borers on maize and elephant grass in the forest zone of Cameroon.

The importance, geographical and temporal distributions of parasitoids of lepidopterous borers on maize and elephant grass, Pennisetum purpureum, were assessed during surveys in farmers' fields in six villages and two on-station trials in the forest zone of Cameroon between 1995 and 1996. The borer species encountered were Busseola fusca (Fuller), Sesamia calamistis Hampson, Eldana saccharina Walker on both host plants, and Mussidia nigrivenella Ragonot on maize only. Busseola fusca was the predominant host accounting for 44-57% and 96% on maize and elephant grass, respectively, followed by E. saccharina on maize with 27-39%. Fifteen hymenopterous, two dipterous and one fungal species were found on these stem and cob-borers. Among those were six pupal, six larval, four egg, one larval-pupal parasitoid and four hyperparasitoids. The scelionid parasitoids Telenomus busseolae Gahan and T. isis Polaszek were found on B. fusca eggs in all locations. During the first season, mean egg parasitism was low and ranged between 3.1% and 27% versus 54-87% during the second season. Species belonging to the Tetrastichus atriclavus Waterston complex were recovered from all four borer species. The majority and most common larval and pupal parasitoid species belonged to the ingress-and-sting guild. Larval and pupal parasitism were very erratic and on more than 50% of the sampling occasions no parasitoids were recovered. Parasitoid diversity was higher on elephant grass than maize.

Monitoring and modeling of field infestation and damage by the maize ear borer Mussidia nigrivenella (Lepidoptera: Pyralidae) in Benin, West Africa.

In many countries in West Africa, the pyralid ear borer Mussidia nigrivenella Ragonot occasionally causes severe damage to pre- and postharvest maize. Between 1992 and 1995, the distribution of and damage caused by M. nigrivenella were studied in Benin using survey data and an on-station field experiment. The borer was distributed across the whole country, and at maturity an average 25% of the ears sampled in maize fields were infested. Damage levels varied with agro-ecological zones and were highest in the Guinea Savannas. However, borer-related yield losses were comparatively low. Three applications of cypermethrin over the growing season did not provide sufficient control in the on-station field experiment. A model was developed to estimate maize losses caused by M. nigrivenella, using the percentage of infested ears, which explained 93% of the variance. Extrapolation of field data indicated a 25% yield loss once a 100% infestation of maize ears was reached. For surveys in maize fields the model is a valid tool for a rapid assessment of crop losses caused by M. nigrivenella.

Host Plants and Population Dynamics of the Ear BorerMussidia nigrivenella(Lepidoptera: Pyralidae) in Benin

The ear borer Mussidia nigrivenella Ragonot is a polyphagous insect pest that feeds on various cultivated and wild plants. Surveys in four agro-ecological zones of Benin, conducted between 1993 and 1997, revealed ≈20 plant species from 11 plant families hosting the borer, but only 13 host plants enable the borer to develop to the pupal stage. Whereas, a maize crop usually supports one generation per season, several generations of M. nigrivenella were recorded on Parkia biglobosa (Jacq.) Benth. and Gardenia spp. Agro-ecological variation in the availability of wild host plants was noticed. The high abundance of wild hosts in the Guinea Savannas reflects the diversity of the natural flora in these zones. This abundance of M. nigrivenella host plants, coupled with their overlapping fruiting periods may be the main reason for the high pest densities on maize, although only one maize crop per year is grown in the Northern Guinea savanna. In a field experiment, the highest infestation levels and densities of M. nigrivenella occurred on Canavalia enseiformis (L.) DC. and Mucuna pruriens DC., two popular cover crops in West Africa. Maize and cotton were about equally suitable hosts. Thus, fruiting periods of C. enseiformis and M. pruriens should not precede that of maize, to avoid emerging M. nigrivenella populations shifting from the cover crops to maize.