Stem Borer Species Research Articles

English

Lepidopteran borers are the most devastating field pests of maize in West and Central Africa. In view of the rapidly changing climate which favours an upsurge of more destructive biotypes of insect pests, diverse sources of resistance from different genetic backgrounds need to be harnessed for crop improvement purposes. Forty tropical maize inbreds comprising adapted and exotic lines from International Institute of Tropical Agriculture (IITA) and International Maize and Wheat Improvement Centre (CIMMYT) maize breeding programs were evaluated for resistance to two species of stem borers- Sesamia calamistis and Eldana saccharina at Ibadan and Ikenne, Nigeria, under artificial infested and non-infested conditions in 2015 and 2016 cropping seasons. The experiment was laid out in a randomized complete block design in three replicates. Data were collected on agronomic traits and stem borer damage parameters. On average, the CML lines had relatively higher grain yield despite the high level of stem tunneling, stalk breakage and cob damage, with the exception of CML 67 (0.19 ton/ha) and CML 71 (0.06 tons/ha). BD 74-395 had the highest yield (1.45 t/ha) among the BDs, despite its high stalk breakage and cob damage. Among IITA lines, KU1414SR/SR, 1368 and 9030STR were the highest yielding with grain yields of 1.71, 1.39 and 1.19 t/ha, respectively. Moderate to high heritability was observed among the stem borer damage parameters. Negative genetic gain was observed in stem tunneling. Mean square of lines was significant for all the traits studied. The top-performing inbreds were similarly grouped using the rank summation index and principal component analysis. The exotic lines had good adaptability and showed potential as sources of stem borer resistance, and could therefore be explored in breeding programs for resistance to Eldana and Sesamia. Key words: Eldana saccharina, maize inbreds, resistance, Sesamia calamistis, tropics. &nbsp

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.

Lepidopterous stem borers of maize (Zea mays): agro-ecological and regional composition and distribution of their parasitoids in Southern Ghana

The study aimed at finding out the level of infestation of maize stem borers, their agro-ecological and regional composition and distribution of their parasitoids. Farms were made at University of Cape Coast in the major and minor cropping seasons and maize sown. Plant infestation was recorded weekly. Stem borer larvae and pupae collected from plants were reared until either parasitoids developed from them or they developed into pupae or adults. Rate of parasitization of each stem borer was calculated. In two national maize field surveys, field infestation by pests and parasitism were determined. Parasitoids that emerged from stem borer larvae and pupae were identified to species level. Diversity and distribution of parasitoids according to agro-ecological zones and national administrative regions were determined. Higher stem borer infestation was recorded in the minor season experimental plants. Also, higher number of stem borers was collected from plants during the minor season. Eldana saccharina was the most parasitized stem borer in the experimental farms. Surveys showed more parasitization of stem borers in the minor season. Ashanti and Western regions recorded the highest diversity of parasitoids and Eastern Region recorded the most abundant parasitoids. From both experimental farm and survey results Syzeuctus sp. was the most important parasitoid species of maize stem borers. These results provide useful information on the biology and activities of parasitoids that can be exploited for managing maize stem borers.

KAJIAN KEBERADAAN LABA-LABA DAN TABUHAN PADA LAHAN PADI SAWAH DALAM MENGENDALIKAN HAMA PENGGEREK BATANG PADI

<em>The results had shown that in the field with the cultivar Mamberamo there were 2 species of the rice stemborers i.e. Scirpophaga innotata and S. Interculas while in the field with the cultivar Superwin there were 3 species of the stemborer i.e. S. Innotata, S. Interculas and Sesamia inferens. On the Mamberamo cultivar the we found the spider spicies Lycosa pseudoannulata and 3 species of bees namely Tetrastichus scnoebii, Telenomus rowani and Stenobracon nucivilliei while on Superwin cultivars we obtain only one spider spicies namely T. Scnoebii, T. rowani and S. nucivilliei and Temolucha philipinensis. The damage caused by the vegetative phase of the rice stemborer on Mamberamo and Superwin was rated as healthy or no damage (0%), while the damage by the generative phase on both rice cultivars was rated as low i.e. 6.07 % and 2.05 % respectively.</em>

Odour and feeding preference of noctuid moth larvae conditioned to vanillin diet and non-vanillin diet

It is largely accepted that larval experience influence host-plant preference of larvae. In general, larval experience with a host plant induces both an odour and feeding preference for that plant. In a previous study, exposure of three noctuid stem borer species, i.e. Sesamia nonagrioides, Busseola fusca and B. nairobica, to a vanillin-enriched medium induced an olfactory preference for the odours of this medium in the larvae of these species. Here, we checked if the exposure to a vanillin-enriched medium also induced a feeding preference for this diet. Different life stages (i.e. neonate larvae to adults) of the three species were conditioned to an artificial diet enriched with vanillin over two generations. Thereafter, two-choice tests on third-generation larvae were done using a Y-tube olfactometer for odour preferences and diet choice experiments. Larvae of all three-species conditioned to the vanillin diet oriented significantly towards the odour of this diet, whereas the non-conditioned larvae did not. Still, apart for B. fusca, the conditioned larvae did not exhibit a feeding preference for this diet, thus odour preference did not match the feeding choice of the conditioned larvae. The implication of this result on insect’s adaptability to a new host plant in a changing environment is discussed.

Influence of prolonged dietary experience during the larval stage on novel odour preferences in adults of noctuid stem borer moths (Lepidoptera: Noctuidae)

In Lepidoptera, larval dietary experience of volatile cues can induce adult preference for these cues. However, such induction may require several generations, depending in part on the degree of specialization of the insects. In a previous study, using species of noctuid stem borers with different diet breadths, namely the polyphagous Sesamia nonagrioides, the oligophagous Busseola fusca and monophagous Busseola nairobica, it was shown that in S. nonagrioides, one generation was enough to induce a preference for vanillin in the resulting gravid females, whereas even two generations failed to induce a response in adults of Busseola spp. In this study, we checked whether a higher number of generations of exposure to a vanillin-enriched medium could induce a significant olfactory preference for this medium in the species B. fusca and B. nairobica, which have narrower host-plant utilization ranges than S. nonagrioides. Larvae were reared to the adult stage on an artificial diet enriched with vanillin for periods of from 2 to 7 or 8 generations, followed by two-choice tests on gravid females using a Y-tube olfactometer. The results showed different responses according to the species: for the oligophagous B. fusca, there was no significant effect of the conditioning, while a significant preference for the odours emitted by this new vanillin-enriched diet was recorded for the polyphagous S. nonagrioides and monophagous B. nairobica, but after different numbers of generations. In conclusion, different diet breadths seem to be associated with different levels of plasticity in the odour preference of adults. The implication of this result for insects' adaptability in a changing landscape is discussed.

Diversity and Abundance of Lepidopteran Stem Borers and Their Respective Native Hosts in Different Vegetation Mosaics in Tanzania

Lepidopteran stem borers are important pests of maize and sorghum in East and southern Africa. Except for Chilo partellus (Swinhoe), the other important lepidopteran pests of maize and sorghum, Busseola fusca (Fuller), and Sesamia calamistis Hampson, are indigenous to the African continent. As some stem borers became pest, some species remained in the natural habitats where they still infest non-cereal host plants. However, understanding the diversity of stem borer species that remained in uncultivated habitats and their role in pest dynamics received little attention in research. With the current changes in the natural habitats, some of the species in these habitats may switch to become pests. In addition to host switch, some of the unknown species currently restricted to natural habitats may disappear altogether. Several studies have been undertaken in Tanzania to assess stem borer species diversity. However, there are challenges in comparing diversity values among different zones due to differences in sampling protocols. In this study, a standardised sampling protocol was used and the paper presents a catalogue of stem borer species and their respective hosts in five different vegetation mosaics in Tanzania.

Superior basal and plastic thermal responses to environmental heterogeneity in invasive exotic stemborer Chilo partellus Swinhoe over indigenous Busseola fusca (Fuller) and Sesamia calamistis Hampson

AbstractLepidopteran stemborers are the most destructive insect pests of cereal crops in sub‐Saharan Africa. In nature, these insects are often exposed to multiple environmental stressors, resulting in potent impact on their thermal tolerance. Such environmental stressors may influence their activity, survival, abundance and biogeography. In the present study, we investigate the effects of acclimation to temperature, starvation and desiccation on thermal tolerance, measured as critical thermal limits [critical thermal minima (CTmin) and maxima (CTmax)] on laboratory‐reared economic pest species Chilo partellus Swinhoe (Lepidoptera: Crambidae), Busseola fusca (Fuller) and Sesamia calamistis Hampson (Lepidoptera: Noctuidae) using established protocols. Low temperature acclimation results in improved CTmin for B. fusca and C. partellus, whereas high temperature acclimation enhances the same trait for B. fusca and S. calamistis. Similarly, high temperature and starvation pretreatment improve CTmax for C. partellus relative to S. calamistis and B. fusca. In addition, starvation and desiccation pretreatments improve CTmin for all stemborer species. Furthermore, rapid cold‐hardening (RCH) enhancs CTmin for B. fusca and C. partellus, whereas rapid heat‐hardening (RHH) improves the same trait for C. partellus. However, RCH and RHH impair CTmax for all stemborer species. These findings show differential thermal tolerances after exposure to heterogeneous environmental stress habitats. Chilo partellus, of exotic origin, shows a higher magnitude of basal thermal tolerance plasticity relative to the indigenous African species S. calamistis and B. fusca. This indicates that C. partellus may have a fitness and survival advantage under climate‐induced heterogeneous environments, and also have a greater chance for geographical range expansion and invasion success compared with the indigenous B. fusca and S. calamistis.

Diversity and abundance of lepidopteran stem borers and their host plants in Ethiopia

AbstractLepidopteran stem borers are among the most important insect pests of maize, sorghum and sugarcane in sub‐Saharan Africa. Except for Chilo partellus, the other stem borer pests in Ethiopia are indigenous to Africa and are assumed to have coevolved with some native grasses and sedges in the natural habitat. In addition to pest species, natural habitats harbour diverse non‐economic stem borer species, some of which are new to science. However, with the growing threats to natural habitats, some non‐economic stem borer species may switch or expand their host ranges to include cultivated crops and evolve as “new” pests. Besides host switch, some of the unknown species currently limited to natural habitats may disappear. We examined the diversity, abundance and interactions of lepidopteran stem borers and their wild host plants in five different vegetation mosaics in Ethiopia. The stem borer species diversity varied among vegetation mosaics and host plants. Forty‐four stem borer species belonging to 14 different genera in the families of Noctuidae, Crambidae, Pyralidae and Tortricidae were recorded from 34 wild host plants and through light trap. Among these families, Noctuidae was the highest in species richness in which 31 species were identified, out of which 15 species and two genera were new to science. This paper discusses the ecological interpretation of host plant–stem borer species interactions, particularly in relation to habitat disturbances.

Lepidopteran Stem Borer Species Abundance and Associated Damages on Irrigated Kilombero Low Land Rice Ecosystem in Tanzania

Lepidopteran Stem Borer Species Abundance and Associated Damages on Irrigated Kilombero Low Land Rice Ecosystem in Tanzania

The Cotesia sesamiae story: insight into host-range evolution in a Hymenoptera parasitoid and implication for its use in biological control programs.

This review covers nearly 20years of studies on the ecology, physiology and genetics of the Hymenoptera Cotesia sesamiae, an African parasitoid of Lepidoptera that reduces populations of common maize borers in East and South Africa. The first part of the review presents studies based on sampling of C. sesamiae from maize crops in Kenya. From this agrosystem including one host plant and three main host borer species, studies revealed two genetically differentiated populations of C. sesamiae species adapted to their local host community, and showed that their differentiation involved the joint evolution of virulence genes and sensory mechanisms of host acceptance, reinforced by reproductive incompatibility due to Wolbachia infection status and natural inbreeding. In the second part, we consider the larger ecosystem of wild Poales plant species hosting many Lepidoptera stem borer species that are potential hosts for C. sesamiae. The hypothesis of other host-adapted C. sesamiae populations was investigated based on a large sampling of stem borer larvae on various Poales across sub-Saharan Africa. The sampling provided information on the respective contribution of local hosts, biogeography and Wolbachia in the genetic structure of C. sesamiae populations. Molecular evolution analyses highlighted that several bracovirus genes were under positive selection, some of them being under different selection pressure in C. sesamiae populations adapted to different hosts. This suggests that C. sesamiae host races result from co-evolution acting at the local scale on different bracovirus genes. The third part considers the mechanisms driving specialization. C. sesamiae host races are more or less host-specialized. This character is crucial for efficient and environmentally-safe use of natural enemies for biological control of pests. One method to get an insight in the evolutionary stability of host-parasite associations is to characterize the phylogenetic relationships between the so-called host-races. Based on the construction of a phylogeny of C. sesamiae samples from various host- and plant species, we revealed three main lineages. Mechanisms of differentiation are discussed with regard to the geography and ecology of the samples. One of the lineage presented all the hallmarks of a distinct species, which has been morphologically described and is now studied in the perspective of being used as biological control agent against Sesamia nonagrioides Lefèbvre (Lepidoptera: Noctuidae), a major maize pest in West Africa and Mediterranean countries (see Benoist et al. 2017). The fourth part reviews past and present use of C. sesamiae in biological control, and points out the interest of such molecular ecology studies to reconcile biodiversity and food security stakes in future biological control.

English

Maize (Zea mays L.) is the staple food in Kenya, and mapping the qualitative trait loci (QTL) associated with resistance to maize stem borer pest is important towards marker assisted breeding for this quantitative trait. The objective of this study was to identify any QTL associated with resistance to Chilo partellus and Busseola fusca, the two important stem borer pests in maize production in Kenya. A total of 203 F2:3 individuals from a cross between CML442, a stem borer susceptible maize inbred line and CKSBL10026, a stem borer resistant maize inbred line; and 152 SNPs were used for mapping the QTL. Data were collected on leaf damage, stem borer exit holes and stem tunneling length as putative stem borer damage traits. A likelihood odds ratio (LOD) scores of 3.0 and maximum recombination frequency of 0.50 were used to declare linkage. LOD scores between 2.5 and 2.9 were considered strong indications of a QTL. Resistance QTL for the three putative traits were detected on chromosomes 1-7 and 9 for both individual locations and stem borer species analysis. In B. fusca sites, one QTL for reduced stem tunnelling was revealed on chromosome 4 while in the C. partellus sites, one QTL for reduced stem tunnelling was identified on chromosome 4 and another for reduced stem borer exit holes was identified on chromosome 5. Phenotypic variances explained ranged from 6 to 10%, suggesting a need to validate these QTL using a larger population and in different environments. Key words: Busseola fusca, Chilo partellus, mapping, quantitative trait loci (QTL), resistance, single nucleotide polymorphisms (SNPs), stem borer.

Cultural practices to reduce damage by borer insects in commercial cultivars of Amaranthus

Stem borer insects are one of the most important pest groups of Amaranthus crops on a global scale. In this study, we evaluated the magnitude of borer herbivory in five cultivars of Amaranthus experimentally in La Pampa, Argentina, during two growing seasons. We tested the effect of several plant attributes of five cultivars of Amaranthus on the herbivory caused by three stem borer species. In turn, we evaluated the effect of cultivar and plant density (both as factors modifying the thickness of the stems) and the effect of cultivar and planting time (both as factors modifying the length of the life cycle of the plants) on the herbivory caused by the stem borers in two cultivars of Amaranthus hypochondriacus.We report a wide variation in the susceptibility of the cultivars to stem borer herbivory and discuss the effects of the plant features investigated. Phenological and morphological features of the stems (especially the diameter) influenced the selectivity of host plants by the adult females. The management practices tested here, including plant density and sowing date manipulations, modified plant structure and consequently influenced the damage by stem borers. High density sown plants presented thinner stems and suffered reduced damage by borers than plants sown at low density, whereas delayed sown plants had thinner stems and were less attacked by borer insects than earlier sown plants. The implementation of these cultural practices seems to be a promising alternative for the management of borer species, to which Amaranthus is particularly vulnerable.

Dominance of spotted stemborer Chilo partellusSwinhoe (Lepidoptera: Crambidae) over indigenous stemborer species in Africa's changing climates: ecological and thermal biology perspectives

Abstract Africa hosts several economically significant lepidopteran cereal stemborer species belonging to the Crambidae, Noctuidae and Pyralidae families. The invasive spotted stemborer (Chilo partellus Swinhoe), which is native to Asia, is one of the most damaging cereal stemborers in Africa. The impact of C. partellus on indigenous stemborer species remains unclear, although recent work demonstrates its increasing ecological influence and numerical advantage over Sesamia calamistis and Busseola fusca in African landscapes. In the present study, we discuss C. partellus dominance under Africa's changing climates and highlight the ecological and thermal physiological factors that may contribute to its dominance over indigenous stemborer species. Chilo partellus is an efficient colonizer and competitor and may have an advantage under limited resources typical under climate change. Its invasion potential may also probably stem from its short generation time, overwintering physiology, temperature and relative humidity resilience, wide host preferences, and asynchrony with its biocontrol agents. Using laboratory experiments, we show that C. partellus has a high basal temperature tolerance and related plasticity compared with S. calamistis and B. fusca. These results indicate that ecophysiology may determine invasion success and thus may explain the relative invasion advantage of C. partellus in African landscapes. We recommend that future climate change work be directed towards more comprehensive stemborer total ecology research, stemborer thermal biology and implications on the efficacy of biocontrol. Specifically, knowledge of stemborer‐natural enemy evolutionary potential is vital for understanding how climate change and variability may shape host‐natural enemy interactions, with implications for pest forecasts, prediction models and pest management.

Insect Resistance Management in Bt Maize: Wild Host Plants of Stem Borers Do Not Serve as Refuges in Africa.

Resistance evolution by target pests threatens the sustainability of Bt maize in Africa where insect resistance management (IRM) strategies are faced by unique challenges. The assumptions, on which current IRM strategies for stem borers are based, are not all valid for African maize stem borer species. The high dose-refuge strategy which is used to delay resistance evolution relies heavily on the presence of appropriate refuges (non-Bt plants) where pests are not under selection pressure and where sufficient numbers of Bt-susceptible individuals are produced to mate with possible survivors on the Bt maize crop. Misidentification of stem borer species and inaccurate reporting on wild host plant diversity over the past six decades created the perception that grasses will contribute to IRM strategies for these pests in Africa. Desired characteristics of refuge plants are that they should be good pest hosts, implying that larval survival is high and that it produces sufficient numbers of high-quality moths. Refuge plants should also have large cover abundance in areas where Bt maize is planted. While wild host plants may suffice in IRM strategies for polyphagous pests, this is not the case with stenophagous pests. This review discusses data of ecological studies and stem borer surveys conducted over the past decade and shows that wild host plants are unsuitable for development and survival of sufficient numbers of stem borer individuals. These grasses rather act as dead-end-trap plants and do not comply with refuge requirements of producing 500 susceptible individuals for every one resistant individual that survives on Bt maize.

Density dependence and temporal plasticity of competitive interactions during utilisation of resources by a community of lepidopteran stemborer species

AbstractInteractions within and between species sharing the same resources are characterised by competition or facilitation, and can be influenced by factors such as larval numbers and phenotypic plasticity of the interactions. The effect of larval density on the survival and relative growth rate of the stemborers Busseola fusca (Fuller) and Sesamia calamistis Hampson (both Lepidoptera: Noctuidae), and Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) were studied, as well as the temporal plasticity of their competitive interactions. These stemborers attack maize crops (Zea mays L.) (Poaceae) in sub‐Saharan Africa. Experiments were conducted in the laboratory under controlled conditions at the optimum development temperature (25 °C) for the three species. Surrogate stems filled with artificial diet were intra‐ and interspecifically infested with larvae of each species. The effect of larval density on competition was studied at low (six larvae) and high (12 larvae) levels of infestation, whereas the temporal plasticity of competition was evaluated at 7, 14, 21, or 28 days after infestation. The two experiments involved single‐ and multi‐species infestation treatments. Larval numbers and wet mass in each artificial stem were recorded in each experiment. Survival and relative growth rate of the three species were significantly higher at low‐infestation levels when facing either intra‐ or interspecific competition. The intensity of competition was also temporally plastic among the species and increased as the duration of competition increased. These results are discussed in terms of general infestations of cereal crops by borers.

THE STEM BORER INFESTATION ON RICE CULTIVARS AT THREE PLANTING TIMES

Stem borer is the second important rice pest after rats in Indonesia. A field trial was conducted in Karawang, West Java in dry season of 2003 to study the effect of planting time on the stem borer infestation on seven rice cultivars. The rice cultivars tested were Fatmawati (new plant type cultivar), Gilirang (semi-new plant type cultivar), Maro and Intani 3 (hybrid rice cultivars), and IR72, Cilosari and IR62 (inbreed rice cultivars). The three planting times (PT) were: (1) the early PT, 14 days before farmer’s PT, (2) the common PT, simultaneously with farmer’s PT, and (3) the late PT, 14 days after farmer’s PT. The trial was arranged in a split plot design with four replications. Planting time is the main plot and rice cultivar is the subplot. Fourteen-day old rice seedlings were transplanted at 25 cm x 25 cm planting distance in a 5 m x 6 m plot size. Species and fluctuation of rice stem borer were determined by using water traps containing four synthetic sex pheromone lures of rice stem borer species as attractant. Results showed that the dominant species of stem borer was yellow stem borer (Scirpophaga incertulas Wlk.). Degree of stem borer infestation depended upon the planting time. Stem borer infestation at the first planting time was higher (average 37.90%) compared to those found at the second and third planting time, i.e. 0.65% and 0.54%, respectively. Rice yields of Fatmawati, Gilirang, Maro, Intani-3, and Cilosari cultivars correlated with the degree of stem borer infestation, but did not correlate with planting time. Cilosari cultivar showed the most tolerant under heavily stem borer infestation. The present study implies that adjustment of planting time is the most feasible effort to reduce stem borer infestation because none of the seven rice cultivars tested were able to minimize damage under heavily infestation of yellow stem borer.

THE STEM BORER INFESTATION ON RICE CULTIVARS AT THREE PLANTING TIMES

Stem borer is the second important rice pest after rats in Indonesia. A field trial was conducted in Karawang, West Java in dry season of 2003 to study the effect of planting time on the stem borer infestation on seven rice cultivars. The rice cultivars tested were Fatmawati (new plant type cultivar), Gilirang (semi-new plant type cultivar), Maro and Intani 3 (hybrid rice cultivars), and IR72, Cilosari and IR62 (inbreed rice cultivars). The three planting times (PT) were: (1) the early PT, 14 days before farmer’s PT, (2) the common PT, simultaneously with farmer’s PT, and (3) the late PT, 14 days after farmer’s PT. The trial was arranged in a split plot design with four replications. Planting time is the main plot and rice cultivar is the subplot. Fourteen-day old rice seedlings were transplanted at 25 cm x 25 cm planting distance in a 5 m x 6 m plot size. Species and fluctuation of rice stem borer were determined by using water traps containing four synthetic sex pheromone lures of rice stem borer species as attractant. Results showed that the dominant species of stem borer was yellow stem borer (Scirpophaga incertulas Wlk.). Degree of stem borer infestation depended upon the planting time. Stem borer infestation at the first planting time was higher (average 37.90%) compared to those found at the second and third planting time, i.e. 0.65% and 0.54%, respectively. Rice yields of Fatmawati, Gilirang, Maro, Intani-3, and Cilosari cultivars correlated with the degree of stem borer infestation, but did not correlate with planting time. Cilosari cultivar showed the most tolerant under heavily stem borer infestation. The present study implies that adjustment of planting time is the most feasible effort to reduce stem borer infestation because none of the seven rice cultivars tested were able to minimize damage under heavily infestation of yellow stem borer.

Relative abundance of stem borer species and natural enemies in rice ecosystem at Madhupur, Tangail, Bangladesh

The relative abundance of different stem borer species and their natural enemies with interaction effects were studied at three growth stages of irrigated Boro rice at Madhupur under the district of Tangail, Bangladesh during January to April, 2013. Five stem borer species viz; Yellow stem borer (Scirpophaga incertulas), Pink stem borer (Sesamia inferens), Dark headed stem borer (Chilo polyhcrysus), Stripped stem borer (Chilo suppressalis), White stem borer (Scirpophaga innotata), and nine different natural enemies were collected from the rice fields and recorded. The population of stem borers and natural enemies was highest in tillering stage and lowest in seedling stage. The relative abundance of stem borer species under investigation showed ranking order; yellow stem borer >dark headed stem borer>pink borer>white borer>stripped stem borer and natural enemies as ladybird beetle >long jawed spider>wolf spider>damselfly>carabid beetle>green mirid bug>lynx spider>dragon fly>ear wig. Populations of all five stem borers were positively correlated with ladybird beetle, wolf spider, long jawed spider, lynx spider, damsel fly, dragon fly, green mirid bug and negatively correlated with carabid beetle and earwig.J. Bangladesh Agril. Univ. 12(2): 267-272, December 2014

Is genome size of Lepidoptera linked to host plant range?

AbstractGenome size varies considerably among organisms, largely as the result of differences in the content of non‐coding and/or repetitive DNA, such as introns, pseudogenes, or transposable elements, as well as whole‐genome duplications. Genome size is known to correlate with metabolic rates. Because polyphagy also affects the metabolism, a correlation between diet specialization and genome size can be expected. To test this hypothesis, a study was undertaken with five closely related species of stem borers which are easy to rear under artificial conditions, namely Busseola fusca (Fuller), Busseola segeta (Bowden), Busseola nairobica Le Ru, Sesamia calamistis Hampson, and Sesamia nonagrioides Lefebvre (all Lepidoptera: Noctuidae). However, as the number of species was too low for correlating diet with genome size in Lepidoptera in general, literature data from 16 Lepidoptera species were used in addition. The results pointed to a relationship between genome size and the insect's host plant range in Lepidoptera, but below the family level only, with larger genomes in polyphagous compared to specialist species. In addition, the genome size appeared to be influenced not only by host plant range but also by environmental/climatic conditions. Studies to test this hypothesis should be done strictly below the family level.