The Influence of Egg Parasitoids Belonging to the Telenomus busseolae (Hymenoptera: Scelionidae) Species Complex on Sesamia calamistis (Lepidoptera: Noctuidae) Populations in Maize Fields in Southern Benin

During the second cropping season of 1992, maize fields in southern Benin were examined twice at the pre-tasselling stage, to assess the abundance of eggs of Sesamia calamistis Hampson (Lepidoptera: Noctuidae) and egg parasitism by Telenomus busseolae Gahan (Hymenoptera: Scelionidae). They were also examined at harvest, to investigate the impact of egg parasitism early in the season on S. calamistis populations, and thus plant growth. S. calamistis eggs were found in 84.0% of the fields and on 16.8% of the plants. The parasitoid was present across the entire survey area, with the rate of egg parasitism averaging 76.4%. On average, 84.1% of the egg masses/field were parasitized, indicating that the parasitoid had a good capacity for searching. The relationship between parasitization rates and egg batch size was best described by a quadratic function, with maximum parasitism of about 95% between 1 and 25 eggs/batch. In a multiple regression analysis involving infestation levels at harvest, and soil and parasitoid variables, the T. busseolae parasitization rate was one of the major factors influencing S. calamistis densities. The yield loss due to S. calamistis decreased with increasing egg parasitism.     

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.     

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.     

Evidence of the establishment of Cotesia flavipes (Hymenoptera: Braconidae), a parasitoid of cereal stemborers,and its host range expansion in Ethiopia

Three lepidopteran cereal stemborers, Chilo partellus (Swinhoe) (Crambidae), Busseola fusca Fuller, and Sesamia calamistis Hampson (Noctuidae) were collected from maize and sorghum in Ethiopia. The noctuid stemborers are indigenous to Africa while C. partellus is an introduced species from Asia. In 1999, the Asian stemborer parasitoid, Cotesia flavipes Cameron (Braconidae) was found to be widespread in Ethiopia, even though it had never been released in the country. In addition to attacking Chilo partellus, Cotesia flavipes was reared from B. fusca and S. calamistis. The origin of C. flavipes in Ethiopia may have been Somalia where it was released in 1997 near the border with eastern Ethiopia. Percent parasitism of borers by C. flavipes was higher in eastern Ethiopia than other surveyed regions, and parasitism was higher in 2000 than 1999. Parasitism was higher when cereals were intercropped with other plants and when wild grass hosts of stemborers were present.     

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.     

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.     

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.     

Natural enemies of the maize cob borer,Mussidia nigrivenella (Lepidoptera: Pyralidae) in Benin,West Africa

Mussidia nigrivenella Ragonot is a pest of maize cobs in West Africa. It significantly reduces maize yields and grain quality, with quantitative losses of 2-25%at harvest, and up to 10-15% indirect losses due to an increase in storage pest infestation levels. Infestation by M. nigrivenella also significantly increased the susceptibility of maize to Aspergillus flavus infection and subsequent aflatoxin contamination. Surveys conducted in different agro-ecological zones of Benin on cultivated and wild host plants during 1994-1997 revealed one egg parasitoid, three larval parasitoids and one pupal parasitoid attacking M. nigrivenella. Egg parasitism was scarce on all host plants sampled and in all four agro-ecological zones. Parasitism by larval and pupal parasitoids was usually less than 10%, and varied with host plant species. Both larval and pupal parasitoids were rare or absent in cultivated maize fields. The solitary chalcidid pupal parasitoid, Antrocephalus crassipes Masi, was the predominant species, contributing approximately 53% of the observed mortality. Logistic regression analysis indicated that this parasitoid was more prevalent on fruits of Gardenia spp. (Rubiaceae) than on the other host plant species including maize used by M. nigrivenella, and was most abundant between February and September. The differences in parasitoid diversity and parasitism between Benin and other regions suggest that there are opportunities for biological control through introduction of exotic parasitoids or using the 'new association' approach, which uses natural enemies of closely related host species that occupy similar ecological niches to the target pest.     

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.     

Disturbance of the rainforest has the potential to enhance egg parasitism of lepidopteran noctuid stemborers in Kisangani,DR Congo

Landscape context influences population dynamics of insects and impacts biological processes within communities. It was expected that anthropogenic disturbances of the rainforest landscape in DR Congo would lead to a decreased level of noctuid stemborer egg parasitism as a consequence of a decoupling between stemborers and their naturally occurring parasitoids through dispersal. To test this hypothesis, noctuid egg batches were collected in maize fields along an anthropogenic disturbance gradient to assess change in the rates of eggs parasitism and maize plant infestation with noctuid egg batches. Our results showed that, in contrast to what was initially expected, egg parasitism increased from less to highly disturbed landscape whereas maize infestation had an inverse tendency. Discovery efficiency and mean egg parasitism were 1.416 and 1.392 times higher, respectively, in the most than in the less disturbed landscape. The numbers of eggs and egg batches per 100 maize plants were 0.55 times and 0.532 times the value in the less disturbed landscape, suggesting a dilution of the stemborer population within a large habitat patch encompassing cultivated fields and the surrounding wild host plants. It was concluded that the presence of suitable host plants enhances noctuid stemborers egg parasitism in adjacent maize fields.     

Colleterial glands of Sesamia nonagrioides as a source of the host-recognition kairomone for the egg parasitoid Telenomus busseolae

Abstract.  The maize stemborer Sesamia nonagrioides glues its egg masses under the leaf sheaths or ear bracts using colleterial gland secretion. In spite of such concealed oviposition sites, these eggs are parasitized by Telenomus busseolae. The colleterial glands of S. nonagrioides are investigated as a possible source of the host-recognition kairomone for T. busseolae . This secretion, applied on glass beads, elicits intense antennal drumming and oviposition probing behaviour in the parasitoid. Through an histochemical study, neutral and acid glycoconjugates are identified as components of the secretion. Finally, using ultrastructural techniques, the colleterial glands are described and classified as comprising class 3 secretory cells.     

Resource allocation and bionomics of indigenous and exotic Cotesia (Hymenoptera: Braconidae) species reared on Sesamia calamistis

The braconid larval parasitoids Cotesia chilonis (Matsumura), C. flavipes Cameron and a strain of Cotesia sesamiae (Cameron) from coastal Kenya, reared at the International Centre of Insect Ecology and Physiology, were introduced at the International Institute of Tropical Agriculture in the Republic of Benin for suitability testing on West African stemborers prior to release. C. chilonis was originally collected in Japan while C. flavipes was imported into Kenya from Pakistan. The host species used was the noctuid Sesamia calamistis (Hampson), the most important noctuid maize pest in the region. All three Cotesia species attacked and successfully developed in 2nd to 6th larval instar of S. calamistis but parasitoid-induced mortality was highest on second instars. On most instars, C. sesamiae and C. flavipes produced larger broods than C. chilonis. Larvae parasitized by C. sesamiae developed to the 6th instar and attained an average larval weight of 353 mg, while larvae parasitized by C. chilonis only molted to the 4th instar and attained a maximum weight of 107 mg. The lower developmental threshold estimated from the non-linear regression of temperature on developmental rate was 15.9, 15.9 and 14.9 degrees C for C. chilonis, C. sesamiae and C. flavipes, respectively, while the maximum temperature was 34.2, 35.2 and 33.8 degrees C, respectively. A maximum of four ovipositions were observed per female during a life span ranging from 1.3 days for C. chilonis and C. flavipes to 1.6 days for C. sesamiae. The largest adult progeny, intrinsic rate of increase and net reproductive rates were recorded at 28 degrees C for all species. However, across temperatures, C. flavipes yielded the highest number of offspring, followed by C. sesamiae and C. chilonis. The sex ratios did not vary significantly with species and temperature. Thus, the reproductive potentials of C. sesamiae and C. flavipes were greater than that of C. chilonis.     

Host plant diversity of Sesamia calamistis: cytochrome b gene sequences reveal local genetic differentiation

Sesamia calamistis Hampson (Lepidoptera: Noctuidae) is one of the indigenous stem borer pests associated with maize ( Zea mays L.) and sorghum [ Sorghum bicolor (L.) Moench] (both Poaceae) in Africa. Its pest status varies across the continent and this has been attributed to variation in diet breadth and ecological preferences among populations. Its larvae were found on 12 plant species during a study initiated at four sites (Muhaka, Mtito Andei, Kakamega, and Suam) in Kenya to estimate its diet breadth and genetic population structure. Ten of the infested plant species belonged to the family Poaceae [ Echinochloa haploclada (Stapf) Stapf, Eleusine corocana L., Eleusine jaegeri Pilg., Panicum deustum Thunb, Panicum maximum Jacquin, Pennisetum purpureum Schumacher, Setaria verticillata (L.) P. Beauv., Sorghum arundinaceum (Desvaux) Stapf, S. bicolor , and Z. mays ]; the other two were Cyperaceae: Cyperus distans L. and Cyperus dives Delile. Combined with collections from other African countries (Uganda, South Africa, Benin, Ghana, Nigeria, and Togo), comparisons of partial cytochrome b sequences revealed the presence of 68 haplotypes that differentiated into clades I and II. In Kenya, the two clades colonized different regions, except in Mtito Andei where they co-existed. Individuals from Mtito Andei could be separated based on their host plants: clade I with 14 haplotypes was found mainly on maize (78.6%), whereas clade II with 10 haplotypes was found mainly among wild host plants (63.6%). Detection of divergence among these clades with cytochrome b suggests that their evolutionary separation may have taken place about one million years ago. This article discusses the potential implication of this differentiation for the management of S .  calamistis as a pest of maize and sorghum in Africa.     

Parasitism in diversified agroecosystems: Phenology ofTrichogramma minutum [Hymenoptera: Trichogrammatidae]

Parasitism ofOstrinia nubilalis egg masses byTrichogramma minutum was observed in maize-bare ground monocultures and polycultures of maize/bean/squash and maize/clover. Parasitism rates were 1.9 times higher in monocultures than in polycultures; seasonal phenology of parasitism, however, was similar in both. Parasitism first occurred during the late whorl/early tassel stage of maize; peak parasitism occurred during the mid to late tassel stage, and then dropped off rapidly. We speculate that direct predation of egg masses, and ammensal preemptive competition for egg masses byColeomegilla maculata may have contributed to the decline in parasitism rates in both monocultures and polycultures during the latter part of the season.      

The Effects of an entomopathogenic fungus, Beauveria bassiana (balsamo) vuillemin (hyphomycetes), on Prostephanus truncatus (horn) (Col.: Bostrichidae), Sitophilus zeamais motschulsky (Col.: Curculionidae), and grain losses in stored maize in the Benin Republic

A fungal entomopathogen, Beauveria bassiana, was used to treat maize ears placed in traditional grain stores against Prostephanus truncatus in a field experiment conducted from September 1997 to March 1998 in the Benin Republic, West Africa. Treatments included oil-based spray with and without conidia, maize stored with and without the husk, and stores with and without artificial infestation. Additional treated ears kept in insect-proof cages under field conditions were sampled weekly and exposed to insects to estimate the virulence and persistence of the pathogen during the storage season. P. truncatus densities were significantly lower in treatments that included conidia, although densities were high in all artificially infested treatments and grain losses were severe. The effect of the pathogen was modeled with an exponential decay function and incorporated in a published P. truncatus simulation model. The effects of hypothetical pathogens with different virulence and persistence characteristics were evaluated in terms of insect density and percentage grain loss.     

Self-, Intra-, and Interspecific Host Discrimination in Telenomus busseolae Gahan and T. isis Polaszek (Hymenoptera: Scelionidae), Sympatric Egg Parasitoids of the African Cereal Stem Borer Sesamia calamistis Hampson (Lepidoptera: Noctuidae)

Oviposition behavior, intra- and interspecific host discrimination, and super- and multiparasitism by the scelionids Telenomus busseolae and T. isis were studied using batches of eggs of the noctuid stalk borer Sesamia calamistis as the host. Both Telenomus species were able to discern eggs already parasitized. As a result, self-superparasitism was only 4.0% for T. busseolae and 5.8% for T. isis. Likewise, intraspecific superparasitism was avoided by both species and was significantly higher for T. busseolae than T. isis, and higher when parasitized eggs were offered immediately (0 h) and after 48 h than after 24 h; apparently, the recognition of parasitized eggs at 24 and 48 h was based on the presence of parasitoid larvae rather than a specific marking substance. Multiparasitism was avoided if the female had a choice between unparasitized and parasitized eggs. In a choice experiment, it was 10.2 and 2.5% for T. busseolae and T. isis, respectively. In a nonchoice experiment, multiparasitism did not vary between species and time treatment; it was low, varying between 9.6 and 24.1%. In the 0-h treatment, T. busseolae always outcompeted T. isis, accounting for 63.4 or 91.7% of the offspring, when T. isis or T. busseolae, respectively, was the first species. In the 24-h treatment, the first species emerged more often than the second did but the host egg mortality, i.e., eggs from which neither borer larvae nor parasitoid emerged, was >40%. Whereas T. busseolae is ubiquitous in Africa, T. isis has never been reported from eastern Africa, and it has been proposed for introduction against the prevailing noctuid pest Bussoela fusca. Based on earlier life table and host suitability studies and on the present findings, it is concluded that T. isis would establish in the midaltitudes but not the highlands of eastern Africa.     

Foraging behavior and life history of the stemborer parasitoidCotesia flavipes (hymenoptera: Braconidae)

The gregarious parasitoidCotesia flavipes (Hymenoptera: Braconidae) attacks larvae of pyralid and noctuid stemborers by entering the stemborer tunnel. The short-range foraging behavior of femaleC. flavipes was studied on stemborerinfested plants, in patches with host-related products and in artificial transparent tunnels. In addition, the longevity under specific conditions and the potential and realized fecundity of femaleC. flavipes were determined. Larval frass, caterpillar regurgitate, and holes in the stem are used in host location byC. flavipes. The response to host products byC. flavipes seems not to be host species specific. FemaleC. flavipes respond to frass from four stemborer species and one leaf feeder. No differences are found in the behavior ofC. flavipes on maize plants infested with the suitable host,Chilo partellus (Lepidoptera: Pyralidae), or the unsuitable host,Busseola fusca (Lepidoptera: Noctuidae). Attacking a stemborer larva inside the stem is risky for the parasitoid. The mortality rate of the parasitoids inside the stem is high: 30–40% of the parasitoids are killed by the spitting and biting stemborer larva.C. flavipes is relatively shortlived: without food the parasitoids die within 2 days; with food and under high-humidity conditions they die within 5–6 days.C. flavipes is proovigenic and has about 150 eggs available for oviposition. A relatively large proportion of the available egg load (20–25%) is allocated to each host, so femaleC. flavipes are egg depleted after parasitizing only five or six hosts.     

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.     

Diversity and distribution of lepidopteran stemborer species and their host plants in Botswana

Lepidopteran stemborers are amongst the most important insect pests of maize, sorghum and sugarcane in sub-Saharan Africa. With the exception of Chilo partellus (Swinhoe), which was accidentally introduced into Africa, the other stemborer pests are indigenous to the continent and have co-evolved with native grasses and sedges. In addition to pest species, wild habitats harbour diverse non-economic stemborer species, some of which are new to science. However, the diversity and distribution of both non-economic and pest species of stemborer are currently mostly unknown in Botswana. Accordingly, country-wide surveys were conducted during 2014/15 and 2015/16 austral summer to determine species diversity and distribution in cultivated and wild host plants of stemborers in Botswana. A total of 1597 stemborer larvae and 228 pupae were collected, constituting 63.1 and 36.9 larvae and 84.8 and 15.2% pupae from cultivated versus wild habitats, respectively. In addition to C. partellus, Sesamia calamistis Hampson and Eldana saccharina Walker which were previously reported, 12 more stemborer species were recorded for the first time in Botswana, including nine undescribed species. These species were from the Sciomesa, Sesamia and Conicofrontia genera and Tortricidae and Pyralidae families. Fourteen wild host and two cultivated host plant species of stemborers were recorded. Chilo partellus was most abundant (89.5%) in cultivated habitats whilst E. saccharina (33.6%) was most abundant in wild habitats. Stemborer species diversity was higher in wild habitats than cultivated. Current results highlight the significance of wild, especially wetland habitats for ecological functions and conservation of lepidopteran stemborer biodiversity.     

Effect of Insecticide Usage on Parasitism of Chortoicetes terminifera (Walker) (Orthoptera: Acrididae)

Parasitism of adult Chortoicetes terminifera by Trichopsidea oestracea Westwood and Blaesoxipha rufipes (Macquart) was assessed to discern any effect of chemical control during an outbreak in the 1995–96 season in eastern New South Wales. In the Moree and Gunnedah regions the effects of ground control of bands and aerial control of bands and swarms on parasitism were compared with untreated controls. In the Hunter region only the effect of ground control of bands could be measured. Within both the Moree and Gunnedah regions there were no differences in parasitism rates by either T. oestracea or B. rufipes which could be attributed to chemical control. Parasitism by T. oestracea was significantly higher in the Hunter region than in all treatments in the Moree and Gunnedah regions, except untreated sites in the Gunnedah region. Parasitism by T. oestracea was significantly higher in the Gunnedah region than in the Moree region. Regional differences in parasitism by T. oestracea are attributed to intrinsic climatic and landuse differences between the regions rather than coincident regional differences in insecticide usage. There were no treatment or regional differences in parasitism by B. rufipes. Parasitism levels recorded during the study were atypically low, a fact attributed to a severe drought which preceded the outbreak. Emigration of C. terminifera took place during the study but is not considered to have affected trends in parasitism.