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Des E. Conlong - One of the best experts on this subject based on the ideXlab platform.
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effect of mass rearing and gamma irradiation on the mating behaviour of Eldana saccharina
Entomologia Experimentalis Et Applicata, 2017Co-Authors: Pride Mudavanhu, Des E. Conlong, Pia AddisonAbstract:At low doses of radiation, F1 sterility of the sugarcane stalk borer, Eldana saccharina Walker (Lepidoptera: Pyralidae), can be attained. This bodes well for progression of the sterile insect technique (SIT) as part of an area-wide integrated pest management strategy against this pest of economic importance. However, success of the SIT is dependent on mating ability and performance of the mass-reared sterile insects once released into the field. Mating behaviour of non-irradiated laboratory-reared male E. saccharina moths and those subjected to radiation (150, 200, or 250 Gy) was investigated in still-air cage laboratory trials. Video technology was used to determine whether mass rearing and irradiation of adult moths altered their performance in lek formation and mating success, compared to their untreated wild counterparts. Mating frequency, mating duration, onset of mating, and calling during the first two scotophase periods following adult eclosion were used to make these assessments. Results indicated that both irradiated and non-irradiated laboratory-reared males are able to form leks and mate with wild females, and are therefore as effective as their wild counterparts with regards to mating performance. However, a quantitative departure of male mating behaviour away from that exhibited by wild males was observed in the non-irradiated and irradiated laboratory males. These commenced calling and mating earlier than wild males in both scotophases, except for those irradiated at 250 Gy in the case of mating onset. The mating duration of treated males was similar to that of the untreated wild males, except for those irradiated at 150 Gy, which was significantly higher. Our study provides evidence that increasing radiation dose negatively impacts on performance of laboratory-produced moths relative to their wild counterparts, which in turn could affect the efficacy of the SIT. At 150 and 200 Gy, these parameters are not affected significantly when compared to untreated wild males, and thus these radiation doses can be used safely. However, at higher doses negative effects do become evident.
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radiation biology of Eldana saccharina lepidoptera pyralidae
Florida Entomologist, 2016Co-Authors: Angela Jasmin Walton, Des E. ConlongAbstract:Laboratory-reared male and female Eldana saccharina Walker (Lepidoptera: Pyralidae: Gallerinae)—a major pest of sugarcane (Saccharum spp.; Poales: Poaceae) in South Africa—were exposed to increasing doses of γ-radiation to assess this species' suitability for the sterile insect technique as part of an area-wide integrated pest management (AW-IPM) program. Irradiated male and female moths were crossed with non-irradiated counterparts and irradiated counterparts at the same radiation dose. Male and female moths were treated with radiation doses of 150, 200, 250, 300 and 350 Gy, and the following crosses were made: irradiated males (T♂) mated with untreated females (U♀) and irradiated females (T♀) mated with untreated males (U♂). Males and females of the T♀ × T♂ cross were exposed to the same radiation doses except in the 350 Gy treatment. Fertility (egg hatch) declined significantly with increasing doses of radiation in all crosses. Female progeny from the T♀ × U♂ and T♀ × T♂ crosses were more sensitive to irradiation than female progeny from the U♀ × U♂ and U♀ × T♂ crosses and were completely sterile when treated with either 200 Gy or 150 Gy. Treated males mated with untreated females still had a residual fertility of 0.19% when exposed to 350 Gy of radiation. The fertility of E. saccharina is therefore sensitive to increasing doses of ionizing radiation and this species is a suitable candidate for further development of the SIT as a component of an AW-IPM program. The fecundity of untreated E. saccharina females mated with irradiated males was not affected by radiation. The availability of a great number of infertile eggs can be regarded as a benefit in a program where natural enemies are combined with the SIT because non-fertile eggs can provide additional hosts for egg parasitoids and be a food source for predators.
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general biology of Eldana saccharina lepidoptera pyralidae a target for the sterile insect technique
Florida Entomologist, 2016Co-Authors: Angela Jasmin Walton, Des E. ConlongAbstract:Abstract Eldana saccharina Walker (Lepidoptera: Pyralidae: Gallerinae) occurs on many graminaceous crops and several wild grasses and sedges throughout Africa. It has been reared at the South African Sugarcane Research Institute (SASRI) since the 1970s to study its biology and behavior, as a host for natural enemies and to provide insect material for the plant breeding program. Studies were completed on laboratory-reared E. saccharina of South African origin to assess fecundity, fertility and male and female mating frequencies. Mean fecundity of E. saccharina was 518 ± 27.5 (mean ± SE) eggs per female, up to a maximum of 798 eggs. Mean egg hatch (fertility) of E. saccharina was 63.2 ± 4.2%. In the laboratory, 56.7% of E. saccharina females mated only once but on average females mated 1.5 ± 0.1 times (maximum of 3). Males mated with a maximum of 6 females per male but on average males mated 3.3 ± 0.7 females. Most matings (93%) occurred on the first and second nights after male emergence, and the females o...
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mating compatibility and competitiveness between wild and laboratory strains of Eldana saccharina lepidoptera pyralidae after radiation treatment
Florida Entomologist, 2016Co-Authors: Pride Mudavanhu, Pia Addison, James E Carpenter, Des E. ConlongAbstract:Abstract The efficacy of the sterile insect technique (SIT) applied as part of area-wide integrated pest management (AW-IPM) depends on efficient transfer of sperm carrying dominant lethal mutations from sterile males to wild females. Success or failure of this strategy is therefore critically dependent on quality and ability of sterile males to search for and copulate with wild females. The African sugarcane borer, Eldana saccharina Walker (Lepidoptera: Pyralidae) is an economic pest of sugarcane targeted for control in South Africa using an AW-IPM approach with a SIT component. As part of further steps towards development of the technique, levels of mating competitiveness and compatibility were assessed by observing the extent to which individuals from different populations interbreed when confined together under both laboratory and semi-field conditions. Three types of pair-wise competition experiments were conducted: non-irradiated laboratory adults vs. non-irradiated wild adults, irradiated (200 Gy) ...
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simulation modelling as a decision support in developing a sterile insect inherited sterility release strategy for Eldana saccharina lepidoptera pyralidae
Florida Entomologist, 2016Co-Authors: L. Potgieter, Jan H Van Vuuren, Des E. ConlongAbstract:Abstract A user-friendly simulation tool for determining the impact of the sterile insect technique/inherited sterility technique (SIT/IS) on populations of the African sugarcane stalk borer, Eldana saccharina Walker (Lepidoptera: Pyralidae) is described in this paper. The simulation tool is based on a spatio-temporal model. The design of the simulation tool is such that it is applicable for use in a number of pest/crop and pest control scenarios. It uses 4 interacting subsystems (pest species population dynamics, crop dynamics, environmental dynamics and economics) within a specified spatial domain. Furthermore, the spatial domain describes the layout of the agricultural crop (position, size, shape, crop age and variety of the different fields contained within the crop area). The pest species population subsystem describes E. saccharina population dynamics (but is designed to also include population dynamics of other pest species) under the influence of the IS technique. The E. saccharina module develope...
Rs Rutherford - One of the best experts on this subject based on the ideXlab platform.
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Eldana saccharina (Lepidoptera: Pyralidae) Resistance in Sugarcane (Saccharum sp.): Effects of Fusarium spp., Stalk Rind, Fibre and Nitrogen Content
African Entomology, 2014Co-Authors: Tendekai Mahlanza, Rs Rutherford, S. J. Snyman, M.p. WattAbstract:Sugarcane cultivar resistance to Eldana saccharina is the best strategy to control the stalk borer. The present study aimed to establish the influence of stalk rind hardness, fibre and nitrogen content, and the effect Fusarium species associated with E. saccharina infestation, on borer damage and performance in different sugarcane cultivars. In two glasshouse trials, larvae were inoculated into 7-month-old stalks of seven cultivars with different E. saccharina resistance ratings via wounds created in the rind. In one of the trials, E. saccharina-beneficial fungal strain Fusarium pseudonygamai SC17 and E. saccharina antagonistic F. sacchari PNG40 were inoculated into the stalk of N41 and NCo376 three weeks before larval inoculation. Rind hardness and fibre content were higher in resistant cultivars and mature stalk parts, whilst nitrogen content was lower in these genotypes and in older tissues. However, E. saccharina survival, damage and growth indicators were not entirely consistent with known resistance...
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Proceedings of The South African Sugar Technologists ' Association- June 1991 DEVELOPMENT OF DEFINED SYNTHETIC DIETS FOR THE CULTURING OF Eldana saccharina
2013Co-Authors: Rs Rutherford, J. Van Staden, I South, African Sugar, Association Experiment Station, Mount EdgecombeAbstract:Essential nutritional requirements have been identified for Eldana saccharina Walker. The synthetic diet wasdeveloped to provide nutrients at levels, as near as possible, to those found in undamaged and damaged (reactive) cane stalks. Sugars, fatty acids, simple phenolics, tannins and amino acid balance were found to influence survival and growth of larvae in culture. Some sugarcane varietal differences in identified biochemical traits will be presented and discussed
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RESISTANCE MECHANISMS OF SOUTH AFRICAN SUGARCANE TO THE STALK BORER Eldana saccharina (LEPIDOPTERA: PYRALIDAE): A REVIEW
2013Co-Authors: Malcom G Keeping, Rs RutherfordAbstract:wax, gene expression Despite plant resistance constituting one of the major defences of South African sugarcane against the stalk borer, Eldana saccharina Walker (Lepidoptera: Pyralidae) (Leslie and Keeping, 1996; Keeping, 1999; Keeping and Govender, 2002), little has been published regarding the mechanisms upon which this resistance is based. This paper reviews published and unpublished information on this subject, in an attempt to synthesise our understanding of the major resistance mechanisms against E. saccharina. The first line of plant defence – ovipositional antixenosis – is apparently unimportant in the E. saccharina-sugarcane interaction. Several studies (Nuss and Atkinson, 1983; Mabulu and Keeping, 1999; Anon, 2003) using potted sugarcane of resistant and susceptible varieties placed in cages in a glasshouse, yielded no evidence that mated female moths preferred certain varieties over others for oviposition. Therefore, it appears that resistance is largely, if not entirely, based on the reaction of the larval stages to physico-chemical factors both on the outside and inside of stalks. Leslie (1993) found that penetration of stalks by neonate larvae in the field over the first fou
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Eldana saccharina sex appeal a future method to monitor and control this pest
84th Annual Congress of the South African Sugar Technologists' Association Durban South Africa 17-19 August 2011., 2011Co-Authors: Vincent Harraca, D.e. Conlong, Rs RutherfordAbstract:The first step towards integrated pest management is the timely detection of pest infestation. Insect traps not only allow detection and monitoring of a pest problem but also provide estimates regarding pest population density. Monitoring pest populations with pheromone-baited traps is one of the most useful applications derived from basic research in chemical ecology. Eldana saccharina Walker (Lepidoptera: Pyralidae) has been an important pest throughout the South African sugar industry for more than 40 years. Nevertheless, a pheromone based monitoring system and the possibility of the use of pheromones in a mating disruption approach to control, remain elusive. In order to investigate the sex pheromone signal sent by E. saccharina males, laboratory based behavioural experiments have revealed different degrees of attraction depending on the sex, condition and age of the moth. Indeed, whereas females and males are both significantly attracted by calling males, only females significantly preferred the odour emanating from male hair pencils, and none reacted to extracts from these hair pencils. In addition, preliminary electroantennography experiments demonstrated that vanillin, previously identified as a major pheromonal compound of E. saccharina, is not detected by the moths. Therefore, a new investigation of the hair pencil gland extract is needed, which could lead to a breakthrough in the understanding of E. saccharina sexual attraction and behaviour.
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fusarium species causing pokkah boeng and their effect on Eldana saccharina walker lepidoptera pyralidae
83rd Annual Congress of the South African Sugar Technologists' Association Durban South Africa 25-27 August 2010., 2010Co-Authors: P Govender, S A Mcfarlane, Rs RutherfordAbstract:Pokkah boeng is a fungal disease that can cause serious yield losses in susceptible varieties. Pokkah boeng is caused by Fusarium, but there is some debate regarding the species involved. Previous research has revealed that some Fusarium species isolated from sugarcane could benefit the development of the stalk borer, Eldana saccharina, a serious pest of sugarcane in South Africa. The aim of this research was to isolate and identify the causal organism of pokkah boeng and to determine the effect of the isolates on the development of E. saccharina. Eight representative isolates were inoculated into pokkah boeng susceptible varieties N34 and N41. Typical pokkah boeng symptoms were evident after three weeks. Isolates inoculated into the pot trial and the isolates obtained from inoculated, symptomatic plants were identified as F. sacchari, F. proliferatum and F. andiyazi. The isolates were included in E. saccharina diet and olfactory choice assays. When compared to controls in the dietary inclusion assays, three isolates were considered to be antagonistic (two identified as F. andiyazi and one as F. proliferatum) to E. saccharina, with the mean mass of surviving larvae being significantly lower than the controls. In this study, no isolates resulted in significantly greater larval mass than the controls. Results from the olfactory choice assays suggested that all isolates were attractive to E. saccharina, with significantly more larvae feeding on inoculated maize kernels than the uninoculated controls.
D.e. Conlong - One of the best experts on this subject based on the ideXlab platform.
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Understanding adoption of push-pull for control of Eldana saccharina Walker (Lepidoptera: Pyralidae) using exploratory network analysis.
2014Co-Authors: Jessica Cockburn, D.e. Conlong, J. Van Den Berg, C. N. BezuidenhoutAbstract:‘Push-pull’, a pest management strategy recommended for control of Eldana saccharina in sugarcane, is currently being implemented as part of an integrated pest management programme in the Midlands North region of KwaZulu-Natal, South Africa. However, adoption of new agricultural practices takes place within a complex system in which social, technical, economic and environmental factors all play a role. Understanding such complex systems is important, but difficult. A novel network analysis method for exploring adoption of new pest management technologies was employed to identify drivers of and barriers to adoption. Analysis of the resulting network indicated that the biggest barriers to adoption were perceived ‘hassle’ and cost of implementation at farm level, and insufficient knowledge of how to implement the technology. The adoption ‘leverage points’ identified in the exploratory network analysis provide opportunities for more relevant and focused extension activities.
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Eldana saccharina (LEP: PYRALIDAE) AND ITS PARASITOIDS AT KINYARA SUGAR WORKS, UGANDA
2013Co-Authors: D.e. Conlong, A MugalulaAbstract:Since 1996, regular surveys have been completed for Eldana saccharina Walker and parasitoids of its different life stages in sugarcane and Cyperus papyrus during visits to Kinyara Sugar Works, Uganda. A complex of dipteran (Tachinidae) and hymenopteran (Braconidae, Ichneumonidae, Bethylidae and Eulophidae) parasitoids have been discovered attacking E. saccharina infesting C. papyrus. One species of Tachinidae and one species of Ichneumonidae have been recorded from E. saccharina attacking very old sugarcane on the estate. This paper lists the parasitoids of E. saccharina found on the estate, and follows the rates of parasitism recorded during visits at different times of the year, and through the years on populations of E. saccharina in C. papyrus wetlands on the estate. Co-operation between SASEX and Kinyara Sugar Works will benefit both institutions through increased knowledge of pest/parasitoid interactions, and thus facilitate establishing laboratory colonies of parasitoids for introduction into infested sugarcane in both countries
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STIMULO-DETERRENT DIVERSION OF Eldana saccharina (LEP: PYRALIDAE) AND XANTHOPIMPLA STEMMATOR (HYMENOPTERA: ICHNEUMONIDAE)- PRELIMINARY RESULTS.
2013Co-Authors: D.e. Conlong, B Kasl, South AfricaAbstract:Plant species emit specific semiochemicals when attacked by insects. These make plants unpalatable or repellant to herbivores, and/or attract natural enemies of herbivores attacking the plant. It is hypothesized that sugarcane, because of selection for higher sucrose, among other required traits over the years, has had the ability to produce semiochemical bred out of modern varieties. This may explain why no parasitoids are found attacking Eldana saccharina Walker in sugarcane, while they are commonly found on this insect in adjacent indigenous host plants. Some plants emit these semiochemicals as natural metabolic by-products. Preliminary work on attractant properties of indigenous grass and legume species on a pupal parasitoid of E. saccharina has been completed. In olfactometer trials, Xanthopimpla stemmator Thunberg was attracted to Melinis repens and the South African variety of M. minutiflora in preference to sugarcane. In cage trials, X. stemmator parasitism (%) was higher on E. saccharina pupae when sugarcane was in association with South African (21%) and Kenyan (33%) M. minutiflora, M. nerviglumis (19%) and Desmodium uncinatum (17%) than when sugarcane was the only plant (14%). Research is continuing on effects of these plants on other indigenous parasitoids, and into the creation of a sugarcane agroecosystem incorporating these plants, thereby reducing E. saccharina populations with no reduction in sugarcane yield
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Proceedings of The South African Sugar Technologists ' Association- June 1984 EVALUATION OF EGG PARASlTOlDS IN THE BIOLOGICAL CONTROL OF Eldana saccharina WALKER (LEPIDOPTERA: PYRALIDAE)
2013Co-Authors: D.e. Conlong, South African, Sugar Association, Experiment Station, H. Hastings, Mount EdgecombeAbstract:A research programme for the biological control of the pyralid sugarcane borer Eldana saccharina Walker is outlined briefly. Trichogramma australicum Girault, Trichogramma sp. and Trichogrammatoidea Eldanae Viggiani are the egg parasitoids used in experimental inundative releases, and the scelionid egg parasitoid Telenomus applanatus Bin & Johnson is used in small-scale experimental inoculative releases. Consideration is given to the behaviour of the parasitoids in relation. to the oviposition habits of the target host. Preliminary results of parasitoid releases are summarized and their implications for future research are discussed
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parental and f1 sterility of Eldana saccharina walker lepidoptera pyralidae
84th Annual Congress of the South African Sugar Technologists' Association Durban South Africa 17-19 August 2011., 2011Co-Authors: Angela Jasmin Walton, D.e. Conlong, M F AddisonAbstract:To assess suitability of Sterile Insect Technique (SIT) as a pest management strategy against Eldana saccharina, laboratory reared adult males and females were exposed to increasing doses of radiation and crossed with non-irradiated counterparts or irradiated counterparts at the same radiation dose. Radiation treated males mated with untreated females, and radiation treated females mated with untreated males, were exposed to radiation doses of 100, 150, 200, 250, 300 and 350 Gray (Gy). Treated females mated with treated males were exposed to the same radiation doses except 350 Gy (no offspring survival). To assess F1 sterility, the surviving progeny from all three crosses were mated with non-irradiated laboratory counterparts or F1 adults of the opposite sex from each radiation dose. Fertility declined significantly at increasing doses of radiation in the parental and F1 progeny crosses of treated males. Treated females mated with laboratory males and those mated with treated males were more sensitive to radiation and were sterile at 200 Gy, while treated males mated with laboratory females still had a residual fertility of 0.19% when exposed to 350 Gy. F1 male and female progeny of treated males mated with non-irradiated counterparts were sterile at 250 Gy, while their male parents’ fertility was 0.82%. These radiation doses are consistent with those used in already established SIT programmes against citrus and deciduous fruit damaging Lepidoptera.
François-régis Goebel - One of the best experts on this subject based on the ideXlab platform.
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Monitoring Eldana saccharina and other arthropod pests in South African sugarcane
2007Co-Authors: Mickael J. Way, François-régis GoebelAbstract:Each year from January to December, field surveys are conducted throughout South African sugarcane primarily for the key pest, Eldana saccharina Walker (Lepidoptera: Pyralidae). Monitoring allows detection of excessive larval infestations for early harvesting to assist in reducing populations on an area-wide scale, selection of suitable carryover fields and inspection of seed cane. During surveying, known arthropod crop spoilers are recorded and staff remain vigilant for possible new arthropod incursions. These data provide information about regional infestations of E. saccharina in the industry. Furthermore, related agronomic information is recorded thus providing evidence to support the value of current management tactics employed to reduce the adverse affects of E. saccharina. Additional applications for the E. saccharina records in the database are being researched such as investigating infestations recorded in different varieties, mapping infestations, and for the production of region loss estimates. (Resume d'auteur)
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Larval performance of the pyralid borer Eldana saccharina Walker and stalk damage in sugarcane: Influence of plant silicon, cultivar and feeding site
International Journal of Pest Management, 2007Co-Authors: Olivia L Kvedaras, François-régis Goebel, Malcom G Keeping, Marcus J ByrneAbstract:Abstract Applied silicon (Si) can improve resistance of plants to insect attack. We investigated the interactions between soil applied Si, sugarcane cultivar, and three documented feeding/penetration sites (internode, leaf bud, and root primordia), each at three heights (top, middle, and base) on the stalk and their effects on stem borer, Eldana saccharina Walker (Lepidoptera: Pyralidae) performance and the stalk damage it inflicts. Four sugarcane cultivars, treated (Si+) and untreated (Si−) with calcium silicate, were artificially infested with E. saccharina and the larvae were examined 21 days later. Silicon treatment significantly increased stalk Si content in all sugarcane cultivars and, overall, significantly reduced borer growth rate and also reduced stalk damage, particularly at the internode. Borer survival and growth rate and stalk damage were lowest at the internode, particularly in Si+ resistant cultivars. Although the internode had the hardest rind, hardness at each site was not significantly ...
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silicon and water stress synergy in resistance of sugarcane cultivars to the stalk borer Eldana saccharina lepidoptera pyralidae
International Sugar Journal, 2007Co-Authors: Olivia L Kvedaras, François-régis Goebel, Malcom G Keeping, Marcus J ByrneAbstract:Silicon (Si) improves plant resistance to insect attack and may also enhance tolerance of water stress. The objective of this study was to evaluate whether Si-mediated resistance of sugarcane to the borer Eldana saccharina Walker (Lepidoptera: Pyralidae) is enhanced by water stress. Sugarcane cultivars, two resistant to E. saccharina (N21, N33) and two susceptible (N26, N11) were grown in a pot trial, in Si deficient river sand with (Si+) and without (Si-) calcium silicate. To induce water stress, irrigation to half of the trial was reduced prior to inoculation with E. saccharina eggs, and harvested 66 days later. Stressed and non-stressed plants of the same cultivar did not differ significantly in Si content. However, Si+ plants exhibited increased resistance to E. saccharina attack. In Si+ cane, E. saccharina larval survival and biomass was lower than in Si- cane, significantly so for stressed, susceptible cultivars N26 and N11, and for larval mass in non-stressed N26. Stalk damage was reduced in Si+ cane, significantly so for the stressed, susceptible cultivars N26 and N11, and non-stressed N26. This study showed that Si provides greater protection against E. saccharina attack in susceptible, water-stressed sugarcane than in non-stressed cane and/or resistant cultivars. (Resume d'auteur)
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Impact on yield due to early and late phase infestation by Eldana saccharina (Lepidoptera: Pyralidae).
2006Co-Authors: François-régis Goebel, Mickael J. WayAbstract:The effects of Eldana saccharina Walker (Lepidoptera: Pyralidae) damage on stalk yield components in field trials are reported. The experiment design involved reducing pest pressure with an insecticide to provide undamaged stalks or applying artificial inoculation techniques to elevate pest pressure to obtain damaged stalks for comparison. At harvest, trial results showed lower biomass, lower sucrose and higher fibre content in stalks that had been infested early in the season when compared with stalks that were infested during the maturation stage of the crop cycle. (Resume d'auteur)
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The status of Eldana saccharina (Lepidoptera: Pyralidae) in the South African sugar industry based on regular survey data.
2005Co-Authors: François-régis Goebel, Mickael J. Way, Christophe GossardAbstract:Local Pest, Disease and Variety Control Committee (LPD&VCC) Eldana saccharina survey records from 2001 to 2003 were analysed to investigate the pest status of this stalk borer in the South African sugarcane industry. Percentage stalks damaged, percentage stalk length red and numbers of larvae per 100 stalks varied in different mill areas, thus confirming previously published patterns. Furthermore, damage levels were higher in the coastal than the inland regions. Higher levels of damage were correlated with older cane, and certain varieties suffered more damage than others. Infestations were lower in small-scale than commercial grower sectors. Higher levels of damage were associated with increased nitrogen applied to fields. An estimated economic injury level is given. (Resume d'auteur)
John S Terblanche - One of the best experts on this subject based on the ideXlab platform.
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Evolved variation in cold tolerance among populations of Eldana saccharina (Lepidoptera: Pyralidae) in South Africa
Journal of evolutionary biology, 2014Co-Authors: Elsje Kleynhans, Desmond E Conlong, Katherine A. Mitchell, John S TerblancheAbstract:Among-population variation in chill-coma onset temperature (CTmin ) is thought to reflect natural selection for local microclimatic conditions. However, few studies have investigated the evolutionary importance of cold tolerance limits in natural populations. Here, using a common-environment approach, we show pronounced variation in CTmin (± 4 °C) across the geographic range of a nonoverwintering crop pest, Eldana saccharina. The outcomes of this study provide two notable results in the context of evolved chill-coma variation: (1) CTmin differs significantly between geographic lines and is significantly positively correlated with local climates, and (2) there is a stable genetic architecture underlying CTmin trait variation, likely representing four key genes. Crosses between the most and least cold-tolerant geographic lines confirmed a genetic component to CTmin trait variation. Slower developmental time in the most cold-tolerant population suggests that local adaptation involves fitness costs; however, it confers fitness benefits in that environment. A significant reduction in phenotypic plasticity in the laboratory population suggests that plasticity of this trait is costly to maintain but also likely necessary for field survival. These results are significant for understanding field population adaption to novel environments, whereas further work is needed to dissect the underlying mechanism and gene(s) responsible.
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host plant related variation in thermal tolerance of Eldana saccharina
Entomologia Experimentalis Et Applicata, 2014Co-Authors: Elsje Kleynhans, Des E. Conlong, John S TerblancheAbstract:Understanding tolerance of thermal extremes by pest insects is essential for developing integrated management strategies, as tolerance traits can provide insights into constraints on activity and survival. A major question in thermal biology is whether thermal limits vary systematically with microclimate variation, or whether other biotic or abiotic factors can influence these limits in a predictable manner. Here, we report the results of experiments determining thermal limits to activity and survival at extreme temperatures in the stalk borer Eldana saccharina Walker (Lepidoptera: Pyralidae), collected from either Saccharum spp. hybrids (sugarcane) (Poaceae) or Cyperus papyrus L. (Cyperaceae) and then reared under standard conditions in the laboratory for 1–2 generations. Chill-coma temperature (CTmin), critical thermal maximum (CTmax), lower lethal temperatures (LLT), and freezing temperature between E. saccharina collected from the two host plants were compared. CTmin and CTmax of E. saccharina moths collected from sugarcane were significantly lower than those from C. papyrus (CTmin = 2.8 ± 0.4 vs. 3.9 ± 0.4 °C; CTmax = 44.6 ± 0.1 vs. 44.9 ± 0.2 °C). By contrast, LLT of moths and freezing temperatures of pupae did not vary with host plant [LLT for 50% (LT50) of the moth population, when collected from sugarcane: −3.2 ± 0.5 °C, from C. papyrus: −3.9 ± 0.8 °C]. Freezing temperatures of pupae collected from C. papyrus were −18.0 ± 1.0 °C and of those from sugarcane −17.5 ± 1.8 °C. The E. saccharina which experienced the lowest minimum temperature (in C. papyrus) did not have the lowest CTmin, although the highest estimate of CTmax was found in E. saccharina collected from C. papyrus and this was also the microsite which reported the highest maximum temperatures. These results therefore suggest that host plant may strongly mediate lower critical thermal limits, but not necessarily LLT or freezing temperatures. These results have significant implications for ongoing pest management and thermal biology of these and other insects.