Lepidopteran cereal stemborers and associated natural enemies on maize and wild grass hosts in Cameroon

Abstract:  In Cameroon, the noctuid Busseola fusca is the most important pest of maize. The braconid Cotesia sesamiae , which is the most common larval parasitoid of noctuid stemborers in eastern Africa, was absent on B. fusca attacking maize. Thus, it is planned to introduce several strains of the parasitoid from Kenya. Pre-release surveys were undertaken in major maize growing areas to catalogue stemborer species, and larval and pupal parasitoids on maize and four wild host plant species. On maize, B. fusca was the predominant borer in all ecozones except for the lowland coastal forest, usually accounting for 60–99%, followed by the pyralid Eldana saccharina in the forest zone and the crambid Chilo sp. in the mid-altitudes. Contrary to what was reported before, the noctuid Poeonoma serrata – and not B. fusca – was the predominant borer on elephant grass, constituting 70–96% of all borers. On wild sorghum in the forest zone, the noctuid Sesamia poephaga was the most abundant species, while on Panicum sp., Chilo sp. predominated. On Setaria megaphylla in the forest zone, Chilo sp. was the most abundant species followed by Busseola quadrata . Busseola fusca was scarce on all wild grass species, indicating that previous reports on the predominance of this pest species on wild host plants were the result of misidentifications. Three tachinid and 16 hymenopteran parasitoids were obtained, most of them from B. fusca and P. serrata , on maize and Pennisetum purpureum respectively. C. sesamiae was scarce and never recovered from B. fusca on maize. In view of the new findings, acceptability and suitability studies involving the different stemborer species identified from wild plant hosts are required to determine if they will form a reproductive sink or perennate C. sesamiae populations during the off-season when maize is scarce and B. fusca is diapausing.     

Long-term seasonal fluctuations of lepidopteran cereal stemborers and their natural enemies on maize and wild host plants in southern Benin

Abstract  The seasonal fluctuation of lepidopteran cereal stemborers on maize and wild host plants (i.e., grasses and a few sedges) was investigated in southern Benin from 1988 to 1998 by time series analysis and repeated-measures analysis of variance (ANOVA). In addition, a walk-in light trap was used to study the flight behavior of adult moths. On both cereals and grasses, the noctuid Sesamia calamistis was the predominant species, followed by the pyralid Eldana saccharina . The noctuid Busseola fusca was rare on both maize and wild host plants. In general, pest populations increased during the course of the year to reach peak densities during the second short rainy season, and then crashed to close to zero during the dry season. On wild host plants, egg masses and other immature stages were collected throughout the year but they were higher on wild grasses than maize during the off-season. Thus wild host plants can be considered as refuge for both borers and natural enemies during the off-season, when maize is not available. However, only four out of the eleven wild host species played a discernable role. S. calamistis egg densities appeared to be influenced by density-dependent factors, suggesting an effect of natural enemies. Temperature and rainfall had a negative effect on egg abundance. Larval parasitism by a Kenyan strain of the braconid Cotesia sesamiae , which was released in southern Benin in the early 1990s, and by the tachinid Sturmiopsis parasitica varied between seasons and years but there were no discernable patterns. For both parasitoids and borer host species, parasitism was positively correlated with trap catches of adult moths. The recovery of C. sesamiae during a 2-year period suggests that the parasitoid has established its population in southern Benin.     

Seasonal Fluctuations of Noctuid Stemborer Egg Parasitism in Southern Benin with Special Reference to Sesamia calamistis Hampson (Lepidoptera: Noctuidae) and Telenomus spp. (Hymenoptera: Scelionidae) on Maize

Parasitism of noctuid stemborer eggs was assessed in monthly surveys in maize fields in southern Benin, from May 1995 to October 1996, and on alternative hosts, i.e. wild grasses, during the dry season from November 1995 to February 1996. Sesamia calamistis was the most prevalent stemborer species, accounting for 98% of the larvae identified from subsamples reared on ear pieces. Egg batch densities ranged between 0.02-0.15 per plant, with lowest densities found during high rainfall periods. 77% of all egg batches were found to be parasitized The egg parasitoids were the scelionids Telenomus busseolae, T. isis , and the trichogrammatid Lathromeris ovicida , accounting for 55.6, 41.6 and 2.8% of total counts, respectively. Parasitism increased in the course of the cropping season and reached peaks of 92 and 86% during the second growing season of 1995 and 1996, respectively. This coincides with the time when farmers have planted a second crop and during a stage when the plants were most attractive and susceptible to S. calamistis attacks. During the dry season, relatively high parasitism was found on maize and wild grasses in inland valleys, and it was concluded that those habitats play an important role in stabilizing the system for both the pest and its natural enemies. As a result, in the Dahomey Gap, which includes parts of Benin, Togo and Ghana, S. calamistis is usually not of economic importance. Although T. busseolae is ubiquitous in Africa, T. isis was only reported from West Africa, including Cameroon. It is recommended that the geographic range of T. isis should be expanded and include East and Southern Africa, where another host, Busseola fusca , is the most important noctuid stemborer pest on cereals.     

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.     

Abundance, dispersion and parasitism of the stem borer Busseola fusca (Lepidoptera: Noctuidae) in maize in the humid forest zone of southern Cameroon

This study was conducted in the humid forest zone of Cameroon, in 2002 and 2003. The main objective was to investigate the effects of intercropping on infestation levels and parasitism of the noctuid maize stem borer Busseola fusca Fuller. Two trials were planted per year, one during the long and one during the short rainy season. Maize monocrops were compared with maize/legume or maize/cassava intercrops in two spatial arrangements: maize on alternate hills or in alternate rows. Spatial analyses showed that the stemborer egg batches were regularly dispersed in the maize monocrop and aggregated in the intercrops, as indicated by b, the index of dispersion of Taylor's power law. Depending on the crop association and planting pattern, intercrops reduced the percentage of plants with stem borer eggs by 47.4-58.4% and egg densities by 41.2-54.5% compared to monocropped maize. Consequently, larval densities were 44.4-61.5% lower in intercrops compared to monocrops. Intercropping maize with non-host plants did not affect larval parasitism. Up to two-fold higher levels of egg parasitism by scelionid Telenomus spp. were recorded in inter- compared to monocrops during the short rainy seasons of 2002 and 2003. No differences were found among the mixed cropping treatments and parasitism was lower during the long compared to the short rainy seasons. It was proposed that differences in levels of parasitism were due to density dependence effects rather than the effect of the presence of non-host plants in the system.     

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.     

Impact of neonicotinoid seed treatments on thrips (Thysanoptera: Thripidae) and soybean yield in Virginia and North Carolina

Currently there are several neonicotinoid insecticide seed treatments registered for use on soybean (Glycine max L.), with disparity in adoption rates in the eastern United States. A complex of seedling insect pests is found in mid-south soybean, but thrips are the primary early season pest of soybean in Virginia and North Carolina. Published knowledge regarding their impact on soybean yield is minimal, as is the impact of thrips on soybean yield; thrips species composition is also understudied. In 2008 through 2010, nine field experiments in Virginia and North Carolina were conducted to evaluate the impact on thrips population dynamics; the influence on yield of neonicotinoid seed treatments, imidacloprid and thiamethoxam, was reported from nine of these experiments. Moreover, thrips species abundance was recorded in three of these experiments. Both imidacloprid and thiamethoxam reduced thrips densities compared with untreated soybean. Thiamethoxam was more effective than imidacloprid in reducing adult thrips densities at 5 wk after planting. Adult densities peaked at 3 wk after planting, followed by larval densities, which peaked at 4 wk after planting. The most abundant thrips species was Frankliniella fusca (Hinds), followed by Neohydatothrips variabilis (Beach). Other common species included F. occidentalis (Pergande) and F. tritici (Fitch). In general, F. fusca was more common earlier in the season, while N. variabilis was more common later in the season. There were no significant differences in yield among any of the treatments or in the untreated controls. Although neonicotinoid insecticides reduced thrips abundance, data collected in these studies demonstrated that there was no positive yield response.     

Effects of nitrogen and potassium combinations on yields and infestations of maize by Busseola fusca (Lepidoptera: Noctuidae) in the humid forest of Cameroon

Field trials were set up in the humid forest zone of Cameroon to investigate the effects of combinations of different rates of nitrogen (N) (0, 60, and 120 kg N ha(-1)) and potassium (K) (0, 80, and 160 kg K ha(-1)) applied to the soil on the incidence and damage of the noctuid stemborer Busseola fusca (Fuller), and on maize, Zea mays L., yield. Each N/K combination had an insecticide control to assess yield losses due to borers. In contrast to N, K had no effect on plant growth and borer incidence and damage. Across seasons and days after planting, total plant dry matter (DM) production increased with N level and it was 1.2-1.9 and 1.7-2.2 times, respectively, higher at 60 and 120 kg N ha(-1) compared with 0 kg N ha(-1). Total DM at harvest was strongly related to the N content of the plant at 63 d after planting. At the early growth stage, borer abundance and stem tunneling tended to increase with N level, but percentages of dead hearts did not vary with treatment. Maize grain yields increased linearly with N level, but grain yield losses decreased depending on season. Grain yield losses were 11-18.2 times higher with 0 kg N ha(-1) compared with 120 kg N ha(-1). The findings so far indicated that, soil application of N improves the nutritional status of maize, which consequently enhanced its tolerance to stemborer attacks. Improving soil fertility can thus be a very effective means of complementing integrated stemborer control in the humid forest zone of Cameroon.     

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.     

Chrysops silacea and C.dimidiata seasonality and loiasis prevalence in the Chaillu mountains, Congo

Seasonal activity of the loiasis vectors Chrysops dimidiata Wulp and Chrysops silacea Austen (Diptera: Tabanidae) was studied during 1987-89 in villages and surrounding forest of the Chaillu Mountains, Congo. Chrysops were captured mainly in the hot rainy season (November-May) and densities of both species were higher in the forest than in villages. C.silacea predominated at all sites and C.dimidiata was rarely found in villages. In the rain forest, between 07.00 and 18.00 hours, 12 times more C.silacea and 3 times more C.dimidiata were collected with hand-nets (range 15-81 per man-day) than were caught in landing/biting collections on human bait. Chrysops man-biting rates were higher in villages closer to the forest, but variations in loiasis prevalence among villagers (microfilaraemia rates 16-37%) were not proportional to the intensity of contact between people and vectors in the villages, indicating that the majority of loiasis transmission probably occurs when people go into the forest.     

The relationship between possum density and browse damage on kamahi in New Zealand forests

To minimize the impacts of introduced pests and to justify and prioritize pest control, managers need to know the relationship between pest density and damage. This relationship can be difficult to quantify because pest impacts can be highly variable. In New Zealand, introduced brushtail possums (Trichosurus vulpecula) browse a wide range of native forest species. However, possum browse is extremely patchy making it difficult to quantify the relationship between density and damage, meaning the benefits of reducing possum densities are poorly understood. We quantified patterns of possum browse on kamahi (Weinmannia racemosa), a common canopy tree species, at 21 forest sites that were repeat‐measured over an 8‐year period in the North Island, New Zealand, during which time possum densities fluctuated widely. We fitted a multilevel statistical model in order to quantify the relationship between possum density and browse damage while simultaneously quantifying how browse varied among trees, sites and years. Higher possum densities were associated with greater browse damage, but browse was also patchily distributed among trees at the same site, and among sites and years for a given possum density. This heterogeneity meant there was no simple density damage relationship, with the relationship differing from tree to tree and among sites and years. Our results show that at most sites reductions in possum density would have little benefit in reducing the probability of heavy browse on kamahi trees, but at a few sites there would be substantial benefits. This approach provides insights into the pattern and potential causes of variability in possum impacts, and a quantitative basis for prioritizing sites for possum control.     

Characterization of eight microsatellite loci in the maize stalk borer Busseola fusca Fuller, 1901 (Lepidoptera: Noctuidae)

The noctuid stem borer Busseola fusca occurs throughout sub‐Saharan Africa, where it is considered as a major pest of corn and sorghum. To understand B. fusca phylogeography, we isolated and characterized eight microsatellite loci in this species. We investigated these loci for polymorphism on a subset sample of individuals from different geographic populations. All loci were polymorphic, showing between four and 10 alleles. Cross‐species amplification of four of these loci was tested on 11 other noctuid species.     

Field parasitism of nontarget weevil species (Coleoptera: Curculionidae) by the introduced biological control agent Microctonus aethiopoides Loan (Hymenoptera: Braconidae) over an altitude gradient

The parasitoid, Microctonus aethiopoides Loan (Hymenoptera: Braconidae) was introduced into New Zealand in 1982 to control the alfalfa pest, Sitona discoideus Gyllenhal (Coleoptera: Curculionidae). Studies have shown that a number of nontarget weevil species are attacked in the field by this parasitoid. A field study was carried out to investigate nontarget parasitism by M. aethiopoides over an altitudinal sequence from the target host habitat (alfalfa) into native grassland. Three locations were selected for the study, and at each, the alfalfa growing in the valley floor was sampled annually for parasitism of the target pest that ranged between 17 and 78%. At progressively higher altitudes, three further grassland sites at each location were sampled monthly during spring to autumn for up to 6 yr. Weevil densities were estimated, species identified, and dissections carried out to determine reproductive status and parasitism. Almost 12,000 weevils were collected during the study, which were identified as 36 species in total from the three locations. Eight weevil species were found to be parasitized, including S. discoideus, the target host that was found at all sites. Parasitism of nontarget species was approximately 2% overall but varied with location, site, and season. Substantial nontarget parasitism was found at only one of the locations, with up to 24% parasitism of a native weevil, Nicaeana fraudator Broun (Coleoptera: Curculionidae), recorded. Another species, Irenimus egens (Broun) (Coleoptera: Curculionidae), was also found at this location at similar population densities but was attacked far less by M. aethiopoides. Results are discussed in relation to weevil phenology.     

Comparison of Herbivores and Herbivory in the Canopy and Understory for Two Tropical Tree Species1

The Janzen–Connell model of tropical forest tree diversity predicts that seedlings and young trees growing close to conspecific adults should experience higher levels of damage and mortality from herbivorous insects, with the adult trees acting as either an attractant or source of the herbivores. Previous research in a seasonal forest showed that this pattern of distance‐dependent herbivory occurred in the early wet season during the peak of new leaf production. I hypothesized that distance‐dependent herbivory may occur at this time because the new foliage in the canopy attracts high numbers of herbivores that are limited to feeding on young leaves. As a consequence, seedlings and saplings growing close to these adults are more likely to be discovered and damaged by these herbivores. In the late wet season, when there is little leaf production in the canopy, leaf damage is spread more evenly throughout the forest and distance dependence disappears. I tested three predictions based on this hypothesis: (1) the same species of insect herbivores attack young and adult trees of a given plant species; (2) herbivore densities increase on adult trees during leaf production; and (3) herbivore densities in the understory rise during the course of the wet season. Censuses were conducted on adults and saplings of two tree species, raribea asterolepis and Alseis blackiana. Adults and saplings of both species had largely the same suite of chewing herbivore species. On adults of Q. asterolepis, the density of chewing herbivores increased 6–10 times during leaf production, but there was no increase in herbivore density on adults of A. blackiana. Herbivore densities increased 4.5 times on A. blackiana saplings and 8.9 times on Q. asterolepis saplings during the wet season, but there were no clear trends on the adults of either species. These results suggest that the potential of adult trees as a source of herbivores on saplings depends on the value of new leaves to a tree species' herbivores, which may differ across tree species.     

Cereal yield losses caused by lepidopterous stemborers at different nitrogen fertilizer rates in Ethiopia

Abstract: Field trials were carried out at three locations in the cool‐wet western and one location in the semiarid eastern ecozones of the Amhara State of Ethiopia to determine the effects of nitrogen fertilizer on pest infestation and yield losses caused by lepidopterous stemborers in maize and sorghum. Three N fertilizer levels, i.e. 60, 120 and 180 kg/ha for maize, and 41, 64, and 87 kg/ha for sorghum, were compared with a zero N treatment. The dominant pest species were the noctuid Busseola fusca (Fuller) and the invasive crambid Chilo partellus (Swinhoe). Leaf N content was positively related to N fertilizer dosage. In general, pest density, parasitism, plant growth and borer damage variables increased with crop growth stage. On sorghum, in the cool‐wet western Amhara, increasing levels of N fertilizer also tended to increase pest density, plant growth and damage variables. In the semiarid ecozone, parasitism by the exotic parasitoid Cotesia flavipes Cameron tended to increase with N level. In the cool‐wet ecozone, sorghum yields increased by up to 74% because of fertilization; losses caused by stemborers decreased linearly with N dosage from 49% to 36%. In maize, because of low borer densities, there were no discernable trends for pest infestation and yield losses. In the cool‐wet ecozone, sorghum yields were positively related to insecticide application and plant height, and negatively to damage variables such as tunnelling and peduncle damage. In semiarid eastern Amhara, the effects of fertilizer on pest, damage and yield were low on both crops because of the higher soil fertility. The results indicate that the profitability of nitrogen fertilizer as an integrated pest management tactic in the control of cereal stemborers depends, among others, on the severity of borer damage and the soil fertility status prevailing in an area. It is concluded that N fertilizer helps minimize the impact of borers on grain yields, especially on sorghum and in the cool‐wet ecozone.     

Relationships of intercropped maize, stem borer damage to maize yield and land-use efficiency in the humid forest of Cameroon

Stem borers are the most important maize pests in the humid forest zone of Cameroon. Field trials were conducted in the long and short rainy seasons of 2002 and 2003 to assess the level of damage and yield reductions caused by stem borers in monocropped maize and in maize intercropped with non-host plants such as cassava, cowpea and soybean. The intercrops were planted in two spatial arrangements, i.e. alternating hills or alternating rows. All intercrops and the maize monocrop were grown with and without insecticide treatment for assessment of maize yield loss due to borer attacks. The land-use efficiency of each mixed cropping system was evaluated by comparing it with the monocrop. The temporal fluctuation of larval infestations followed the same pattern in all cropping systems, but at the early stage of plant growth, larval densities were 21.3-48.1% higher in the monocrops than in intercrops, and they tended to be higher in alternating rows than alternating hills arrangements. At harvest, however, pest densities did not significantly vary between treatments. Maize monocrops had 3.0-8.8 times more stems tunnelled and 1.3-3.1 times more cob damage than intercrops. Each percentage increase in stem tunnelling lowered maize grain yield by 1.10 and 1.84 g per plant, respectively, during the long and short rainy season in 2002, and by 5.39 and 1.41 g per plant, respectively, in 2003. Maize yield losses due to stem borer were 1.8-3.0 times higher in monocrops than in intercrops. Intercrops had generally a higher land-use efficiency than monocrops, as indicated by land-equivalent-ratios and area-time-equivalent-ratios of >1.0. Land-use efficiency was similar in both spatial arrangements. At current price levels, the net production of mixed cropping systems was economically superior to controlling stem borers with insecticide in monocropped maize. The maize-cassava intercrop yielded the highest land equivalent ratios and the highest replacement value of the intercrop. At medium intensity cropping this system is thus recommended for land-constrained poor farmers who do not use external inputs such as fertilizer and insecticides.     

Effect of cropping systems on cereal stemborers in the cool‐wet and semi‐arid ecozones of the Amhara region of Ethiopia

1 Field experiments were conducted on maize and sorghum at three locations in the Amhara state of Ethiopia to determine the effects of mixed cropping on stemborer infestation, borer natural enemies and grain yields. In the cool‐wet ecozone of western Amhara, sole maize was compared with maize intercropped with faba bean, mustard, potatoes and cowpea. In the semi‐arid ecozone of eastern Amhara, the trial was conducted on both maize and sorghum with the companion crops haricot bean, sesame, cowpea and sweet potatoes. 2 The results showed that the predominant borer species in western and eastern Amhara were, respectively, Busseola fusca and Chilo partellus. In Addis Zemen, western Amhara, maize intercropped with mustard and potatoes had significantly lower pest numbers and percent tunnelling than other intercrops and the maize monocrop during the vegetative stage. In eastern Amhara, the cropping system did not significantly affect pest densities but damage to stem, ear or heads tended to be greatest when cereals were intercropped with sweet potatoes. 3 Parasitism of C. partellus by the braconid Cotesia flavipes was greater on maize than sorghum, and on maize it was greater with sweet potatoes than in other intercrops or sole maize. Cocoon mass number per plant did not vary significantly between treatments. 4 There were significant differences between treatments in yields of both sorghum and maize (per plant and per unit area) with the lowest yields observed when they were intercropped with a tuber crop. 5 The results suggest that simultaneous planting of the crop species selected has little advantage over monocropped maize.     

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 small mammals and birds in transport of matter through the shore zone of lakes

An attempt was made to estimate the role of small mammals and birds in the cycling of nutrients in the littoral zone of lakes. We estimated the approximate amounts of food, organic matter and elements ingested and egested during the breeding season by waterfowl. Small mammal densities were estimated, and their movements studied between different patches of a mosaic landscape, including the lake's shore region. Studies on passerine birds were aimed at determining the territories of some species in alder forest. Special attention was paid to the range of penetration of the reed belts by forest species.     

Bird communities of dry forests and oak woodland of western Mexico

Bird species-richness and densities were studied in spring and autumn of 1991 and 1992 in dry forest and oak woodland in western Mexico. Classification of the vegetation resulted in the identification of six dry forest types: from thorn forests, dominated by Acacia , through broad-leaved tree forest (typical dry forest of western Mexico) and small-leaved tree forest to Ipomoea forest. Oak woodland and mixed woodland, which are a transition between dry forest and the more mesic oak woodland, formed two further forest types. In the study area as a whole, bird densities were higher in autumn, following the rainy season, than in spring, which is the dry season, and the beginning of the breeding season. Densities in the two autumns were very similar (mean 93 ± 7.8 birds per 2.8 ha) but differed significantly between spring 1991 (57 ± 2.2 per 2.8 ha) and spring 1992 (70 ± 3.2 per 2.8 ha), possibly due to unseasonal rain in 1992. In autumn, bird densities were highest in thorn forests and lowest in broad-leaved tree forests and oak woodland. In spring 1991, bird densities were highest in Prosopis thorn forest and mixed woodland, and lowest in oak woodland. Bird species-richness was low in oak woodland, in both seasons, and high in mixed woodland and Ipomoea forest in spring. Bird species composition between forest types was more similar in the spring than autumn. The spring similarity in species composition is explained by the presence of generalist species in times of food scarcity during the dry season, and by the homogeneity of the predominantly leafless vegetation. Comparison with the bird species composition of a dry forest in Venezuela and the Pacific coast of Mexico indicates that the sites in the present study have an intermediate number of species. Although the present study recorded a smaller number of bird species than on the Pacific coast, 16 were different, expanding the total for Mexican dry forest by 14% from 118 to 134.