D. E. Conlong

Bt-maize as a potential trap crop for management of Eldana saccharina Walker (Lep., Pyralidae) in sugarcane.

Abstract:  Notwithstanding the introduction of several pest management tactics, the stalk borer Eldana saccharina Walker (Lep., Pyralidae) remains the most serious pest in South African sugarcane. A novel tactic for managing this pest in sugarcane would be the use of a dead‐end trap crop that attracts moths for oviposition and curtails subsequent larval development, thereby reducing pest population size. Glasshouse bioassays, in which moths chose to oviposit on maize producing Bacillus thuringiensis Cry1Ab toxin (Bt‐maize), non‐Bt‐maize or sugarcane of two cultivars (borer‐resistant and ‐susceptible), showed that E. saccharina laid significantly more eggs and egg batches per dry leaf and unit mass of dry leaf on maize (Bt or non‐Bt) than on either of the cane cultivars. When moths had a choice of ovipositing on 2‐, 3‐, 4‐ or 5‐month‐old maize (Bt and non‐Bt), dry leaf number and mass of dry leaf material was significantly correlated with number of eggs and egg batches, indicating that older plants, which carried larger amounts of dry leaf matter, were more attractive for oviposition. Finally, glasshouse assays in which hatching larvae fed on 2.5‐, 3.5‐ and 4.5‐month‐old Bt and non‐Bt‐maize plants, showed that the Cry1Ab toxin was effective in killing E. saccharina larvae in all Bt‐maize plant growth stages, confirming that Bt‐maize fulfilled the third requirement (curtailing larval development) of a dead‐end trap crop for this pest. We argue that Bt‐maize warrants further testing in the field as a trap crop, both alone and as a component of a ‘push–pull’ or habitat management system for E. saccharina in sugarcane.

Beauveria brongniartii on white grubs attacking sugarcane in South Africa.

Beauveria brongniartii (Saccardo) Petch fungal infections were observed on the melolonthid Hypopholis sommeri Burmeister (Coleoptera: Scarabaeidae) at two sites (Harden Heights and Canema) in the sugarcane producing area of the northern KwaZulu-Natal Midlands of South Africa. To initially identify the disease-causing fungus, 17 different fluorescently-labelled microsatellite PCR primers were used to target 78 isolates of Beauveria spp. DNA. Microsatellite data resolved two distinct clusters of Beauveria isolates which represented the Beauveria bassiana s.s. (Balsamo) Vuillemin (17 isolates) and B. brongniartii (60 isolates) species groups. These groupings were supported by two gene regions, the nuclear ribosomal Internal Transcribed Spacer (ITS) and the nuclear Bloc gene of which 23 exemplar Beauveria isolates were represented and sequenced. When microsatellite data were analysed, 26 haplotypes among 58 isolates of B. brongniartii were distinguished. Relatively low levels of genetic diversity were detected in B. brongniartii and isolates were shown to be closely related. No genetic differentiation was observed between the Harden Heights and Canema populations; they thus may be considered one, structured and fragmented population over a distance of 5.5 km. Historically high levels of gene flow from swarming H. sommeri beetles is the proposed mechanism for this observed lack of genetic differentiation between populations. Microsatellite analyses also showed that B. brongniartii conidia were being cycled from arboreal forest to subterranean sugarcane habitats and vice versa in the environment by H. sommeri life stages. This is the first record of this species of fungus infecting H. sommeri larvae and adults in South Africa.

Integrative taxonomy of Acrapex stem borers (Lepidoptera : Noctuidae : Apameini): combining morphology and Poisson Tree Process analyses

Abstract. Ten morphologically similar species of Acrapex from eastern and south-eastern Africa belonging to the A. stygiata and A. albivena groups are reviewed. Six species are described as new: A. brunneella, A. mitiwa, A. mpika, A. salmona, A. sporobola and A. yakoba. The Poaceae host plants of eight species are recorded; four species, A. mitiwa. A. subalbissima, A. syscia and A. yakoba, were found developing exclusively on Imperata cylindrica (L.) Beauv., (Andropogoneae); two species, A. sporobola and A. salmona, on I. cylindrica and Sporobolus macranthelus Chiov. (Zoysieae); and A. albivena on I. cylindrica, Miscanthus capensis (Nees) Andersson (Andropogoneae) and Cymbopogon sp. (Andropogoneae). Acrapex stygiata larvae developed on M. capensis and Cymbopogon sp. The host plants of A. brunneella and A. mpika remain unknown. We also conducted molecular phylogenetics and molecular species delimitation analyses on a comprehensive sample of 49 specimens belonging to nine of the studied species. Molecular phylogenetics and molecular species delimitation analyses provided additional evidence of the validity of the six newly described species but also suggested a level of hidden biodiversity for one of them.

DNA identification of Busseola (Lepidoptera: Noctuidae) larvae in Ethiopian sugarcane

Noctuidae is one of the largest lepidopteran families, encompassing about 20 000 species (Holloway 1998). Some 157 described species of Noctuidae are known to be cereal stem borers in the Afrotropical region (Moyal 2006) and the most economically important of these belong to the genera Busseola and Sesamia. Accurate identification of pest species is the first and most fundamental step to developing sound pest management strategies (Szalanski et al. 2003). However, many of these closely related stem borers are difficult to distinguish from each other morphologically, and no key is available to cover all noctuid stem borers (Holloway 1998).

Morphological reinforcement, ancient introgressive hybridization and species delimitation in African stem-borer species of the genus Sesamia Guenée (Lepidoptera: Noctuidae)

Species delimitation, an issue central to systematics and biodiversity studies, is addressed in the epunctifera group of the stem borer genus Sesamia Guenée (Lepidoptera: Noctuidae). This group is composed of four sub‐Saharan species: Sesamia poephaga Tams & Bowden; Sesamia epunctifera Hampson; Sesamia penniseti Tams & Bowden; and Sesamia poebora Tams & Bowden, the taxonomic status of which was unclear. The first species was considered a possible synonym of the second, and the third species was considered a possible synonym of the fourth. An analysis combining morphological, ecological and molecular data enables us to conclude that S. epunctifera and S. poephaga are different species, and that S. poebora is a synonym of S. penniseti. Two new species were discovered: Sesamia firmatasp.n. and Sesamia veronicasp.n.Sesamia firmatasp.n. has atypical genitalic morphology, suggesting a strong selection resulting in a reinforcement of pre‐zygotic isolation. Some specimens previously identified as S. penniseti on the basis of morphology are sisters to S. epunctifera on the mitochondrial tree, and are connected to S. penniseti on the nuclear tree. The mitochondrial distance from S. penniseti and S. epunctifera is 7.6% and 3.9%, respectively, suggesting an ancient mitochondrial introgression from S. epunctifera into S. penniseti. The possible causes of the reinforcement and introgressive hybridization are discussed. This case of mitochondrial introgression, uncommon in Lepidoptera, in which females are the heterogametic sex, may be an exception to Haldanes rule. The hybrid is assigned the rank of species and named Sesamia pennipunctasp.n.

Virulence of Beauveria brongniartii and B. bassiana against Schizonycha affinis white grubs and adults (Coleoptera: Scarabaeidae)

Two endemic scarab pests, Schizonycha affinis Boheman and Hypopholis sommeri Burmeister (Coleoptera: Melolonthinae) have increased in prevalence in the sugarcane producing regions of the KwaZulu‐Natal Midlands, South Africa. The crop losses associated with their feeding, the failure of chemical insecticides applied for their control, and the recent discovery of Beauveria brongniartii (Sacc.) Petch (Ascomycota: Cordycipitaceae) epizootics on these pests, have generated interest in the development of a mycoinsecticide targeting adults and larvae of these species. Previous research, using microsatellite markers, identified low levels of genetic diversity among isolates of B. brongniartii collected from two field sites where epizootics occurred. The virulence of 21 of these closely related B. brongniartii isolates and two isolates of Beauveria bassiana (Balsamo) Vuillemin was evaluated. Bioassays were conducted against adults and larvae of S. affinis, and adult Tenebrio molitor (L.) (Coleoptera: Tenebrionidae) as a surrogate test insect. The closely related B. brongniartii isolates varied significantly in their virulence towards both S. affinis (50.1–95% mortality) and T. molitor (39–74% mortality), with a number of these not highly virulent against either of these insect species. Those isolates sharing a haplotype did not vary in virulence. Adults of S. affinis were more susceptible than larvae to isolates of B. brongniartii. The median lethal concentration (LC50) required to kill half the adult S. affinis test insects was 7.65 × 106 conidia per millilitre. Schizonycha affinis second instar larvae had a median survival time of 17.5 days when exposed to some B. brongniartii isolates; however, third instars survived significantly longer with a median of 21 days. Third instars exposed to the highest concentration of B. brongniartii isolate HHWG1 survived for a median time of 15 days. Bioassays supported the finding that genetically closely related isolates may vary in their virulence, even if they were obtained from the same field epizootics.

Buakea (Lepidoptera: Noctuidae), a new genus of African stem borers: morphological, ecological and molecular data

A new genus of African stem borers of the subtribe Sesamiina (Lepidoptera: Noctuidae), Buakea gen. n., is described as well as the three species it includes, two new, B. venusta sp. n. and B. kaeuae sp. n., and a species that until now was placed in the genus Busseola Thurau, B. obliquifascia (Hampson) comb. n. The three species are monophagous on different graminaceous host plants, and the two sister species B. kaeaue and B. obliquifascia were collected in different ecological zones and altitudes, which suggests an ecological mode of speciation. Bayesian and maximum likelihood phylogenies inferred from two mitochondrial genes showed that the genus is monophyletic and does not share a recent common ancestor with the genus Busseola. However no strongly supported phylogenetic relationship could be established with the other six genera of the subtribe included in the analysis.

A revision of the genus Conicofrontia Hampson (Lepidoptera, Noctuidae, Apameini, Sesamiina), with description of a new species: new insights from morphological, ecological and molecular data

The aim of this study was to review the species of Conicofrontia Hampson, a small genus of noctuid stem borers (Noctuidae, Apameini) that is distributed in East and Southeastern Africa. We review the morphology of species in this group and provide new diagnoses and ecological data for five species. The following taxonomic changes are proposed: Hygrostola dallolmoi (Berio, 1973) (= Conicofrontia dallolmoi Berio, 1973) comb. n. and Conicofrontia bipartita (Hampson, 1910) (= Phragmatiphila bipartita Hampson, 1910) comb. n., stat. rev. One new species is also described: C. lilomwa, sp. n. from Tanzania. Wing patterns as well as male and female genitalia of the five species are described and illustrated. Finally we carried out molecular phylogenetic and molecular species delimitation analyses on a multi-marker dataset of 31 specimens and 15 species, including the five mentioned species. The results of molecular analyses provide a clear support for the proposed taxonomical changes.

Ecological Genetics and Host Range Expansion by Busseola fusca (Lepidoptera: Noctuidae)

ABSTRACT The host plant range of pests can have important consequences for its evolution, and plays a critical role in the emergence and spread of a new pest outbreak. This study addresses the ecological genetics of the indigenous African maize stem borer, Busseola fusca (Fuller) (Lepidoptera: Noctuidae), in an attempt to investigate the evolutionary forces that may be involved in the recent host range expansion and establishment of this species in Ethiopian and southern African sugarcane. We used populations from Ethiopia, Zimbabwe, and South Africa to examine whether the host range expansion patterns shared by the Ethiopian and the southern African populations of B. fusca have evolved independently. Base-pair differences in the cytochrome oxidase I (COI) gene were used to characterize haplotype diversity and phylogenetic relationships. There were seven haplotypes among the 30 sequenced individuals collected on four host plant species from 17 localities in the four countries. Of the seven COI haplotypes identified, the two major ones occurred in both sugarcane and maize. Genetic analyses revealed no detectable genetic differentiation between southern African B. fusca populations from maize and sugarcane (FST = 0.019; P = 0.24). However, there was strong evidence of variation in genetic composition between populations of the pest from different geographic regions (FST = 0.948; P < 0.001). The main implication of these findings is that the B. fusca populations in maize in southern Africa are more likely to shift to sugarcane, suggesting that ecological opportunity is an important factor in host plant range expansion by a pest.

Record of Eldana saccharina Walker (Lep, Pyralidae) in inland South Africa and its genetic relationship with the coastal population

Surveys to investigate the distribution and abundance of stem borers in natural habitats were conducted in February 2006 and January–February 2007. The surveys included eastern, northern and central parts of South Africa as well as three localities in Lesotho. During the surveys, Eldana saccharina Walker was recovered from three new localities in inland South Africa and two new indigenous hosts, Phragmites australis Cav. and Panicum maximum Jacq. from Boskop in the North‐West Province and Oribi Gorge in KwaZulu‐Natal respectively. Populations of E. saccharina in different parts of Africa are known for their differences in larval feeding behaviours, host plant choice and natural enemies. It is important to understand the origin of the newly recovered population for prevention of incursion and efficient management in case it invades crops. Molecular analysis indicated that the populations recovered in these new locations and from the new host plants are part of the southern African population of E. saccharina. With change in climate, and disturbance in wetlands the insect is expected in the future to be more abundant and problematic in inland areas of southern Africa.