Differences In Larval Mortality Research Articles

TOXICITY OF SOME INSECTICIDES AND THEIR SUBLETHAL EFFECTS ON NUTRITIONAL INDICES OF FALL ARMYWORM IN SWEET CORN PLANT

Corn is a vital cereal crop in Bangladesh, significantly contributing to food security and economy. However, the fall armyworm Spodoptera frugiperda, poses a severe threat to corn cultivation. This study evaluates the toxicity of four insecticides and their effect on the nutritional indices of fall armyworm. Experiment was conducted from November 2022 to April 2023 with sweet corn variety BU Misty Vutta 1 at Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur, Bangladesh. In this research four insecticides: Winmax 40 WDG, Ripcord 10 EC, Marshal 20 EC, and Shobicron 425 EC, were tested on fall armyworm larvae at multiple concentrations. The mortality of fall armyworm larvae was observed at 24, 48, 72, and 96 hours after treatment. Results indicated significant differences in larval mortality across treatments, with Shobicron 425 EC showing the highest mortality rate (100% at 72 hours after treatment), while Winmax 40 WDG showed the lowest. The median lethal concentration (LC50) and lethal concentration for 95% mortality (LC95) values supported the findings, with Shobicron 425 EC demonstrating superior efficacy. Additionally, Shobicron 425 EC resulted in the lowest food consumption (0.1), consumption index (0.2), Approximate digestibility (19.5%), Efficiency of conversion of ingested food (3.9%) and Efficiency of conversion of digested food (1.1%). The study concludes that Shobicron 425 EC is the most effective insecticide for controlling fall armyworm in sweet corn, suggesting its potential for integrated pest management strategies.

Development of novel betabaculovirus (HycuGV-Hc1) as a biopesticide (HycuGV-TR61) and its efficacy on the fall webworm, Hyphantria cunea Drury (Lepidoptera: Erebidae) larvae

BackgroundThe aim of this study was to develop an oil formulation from a local betabaculovirus. Hyphantria cunea Drury (Lepidoptera: Erebidae) granulovirus (HycuGV-Hc1) was isolated from the infected larvae to test its efficacy on the pest. The oil formulation was prepared by mixing the viral suspension with sunflower oil and some adjuvants and named HycuGV-TR61. Crude virus and the formulations were carried out on third instar H. cunea larvae using 1 × 104–8 OBs /ml concentrations and were exposed to temperatures (28, 35, and 42 °C) and UV-B light at different periods (0, 1, 3, 5 h).ResultsThe mortality rate, which was 50% at the lowest concentration (1 × 104 OB/ml), reached 99.86% at the highest concentration (1 × 108 OB/ml). LC50 values of fresh and old forms were calculated as 0.64 × 104 and 0.87 × 104 OBs/ml, respectively. Application of shelf life showed that there was non-significant change in the pathogenic activity of the formulation with time. In the experiments, it was observed that the activity decreased as the temperature and time of exposure increased. Significantly difference in larval mortality was observed when fresh and old formulations were exposed to 0, 1, 3 and 5 h to UV-B, (old: 96.7, 86, 80 and 60%; fresh: 97.1, 90, 85 and 62%, respectively).ConclusionsThe results revealed superior aspects of HycuGV-TR61, which was developed as a local viral biopesticide, its resistance to abiotic factors and its potential to be used in pest control.

Larvicidal activity of different plant parts of Asparagus setaceus against dengue vector Aedes aegypti

Plant-based natural products are preferred over synthetic insecticides because natural products are eco-friendly and much less prone to the development of resistance. This has necessitated research for the development of the eco-friendly, biodegradable indigenous method for the control of vectors. Mosquito larvicidal efficacy of crude and ethanol extracts of the leaf, bark, root, and fruit of Asparagus setaceus (Asparagaceae) against Aedes aegypti was evaluated in the present study. Phytochemical screening of all the plant parts was also done. Crude and ethanol extracts of different parts of A. setaceus showed efficient larvicidal properties against Ae. aegypti in the following descending order fruit> root> bark> leaf. Fruit ethanolic extract exhibited the highest mortality (100%) against 1st and 2nd instars larvae at 24 hours of exposure. The result of the three-way factorial ANOVA of an ethanolic extract with different plant parts, different time intervals, and different instars revealed a significant difference in larval mortality (P

Horizontal Honey-Bee Larvae Rearing Plates Can Increase the Deformation Rate of Newly Emerged Adult Honey Bees.

Simple SummaryRearing honey bee (Apis mellifera) larvae in vitro is an important method for studying bee larvae diseases or the toxicity of pesticides on bees. Laboratory experiments for bee larvae are usually performed by placing a rearing plate horizontally during all developmental stages. However, recent studies have demonstrated that a horizontal rearing environment can cause the deformation of emerged bees. Most studies adopted a vertical rearing method to reduce such deformation, but there is a lack of information on the emergence rates and deformation rates of bees reared on vertical or horizontal plates. Therefore, in this study, we examined the effect of placing the plates vertically and horizontally on newly emerged bees. There were no significant differences in larval mortality, pupal mortality, and adult emergence rates between horizontal and vertical rearing plates. However, the adult deformation rates of the horizontal plates were significantly higher than those of the vertical plates. In conclusion, we suggest that the vertical rearing method is more suitable when considering the deformation rate of the control group to verify the sublethal effects of pesticides on honey bees.Rearing honey bee larvae in vitro is an ideal method to study honey bee larval diseases or the toxicity of pesticides on honey bee larvae under standardized conditions. However, recent studies reported that a horizontal position may cause the deformation of emerged bees. Accordingly, the purpose of this study was to evaluate the emergence and deformation rates of honey bee (Apis mellifera ligustica) larvae reared in horizontal and vertical positions. The study was conducted under the same laboratory conditions with three experimental groups, non-capped or capped horizontal plates and capped vertical plates. However, our results demonstrated that the exhibited adult deformation rates of the horizontal plates were significantly higher (27.8% and 26.1%) than those of the vertical plates (11.9%). In particular, the most common symptoms were deformed wings and an abnormal abdomen in the horizontal plates. Additionally, adults reared on horizontal plates were substantially smaller (10.88 and 10.82 mm) than those on vertical plates (11.55 mm). Considering these conclusions, we suggest that a vertical rearing method is more suitable when considering the deformation rates of the control groups to verify the sublethal effects of pesticides on honey bees.

Evaluating toxicity of Varroa mite (Varroa destructor)-active dsRNA to monarch butterfly (Danaus plexippus) larvae.

Varroa mites (Varroa destructor) are parasitic mites that, combined with other factors, are contributing to high levels of honey bee (Apis mellifera) colony losses. A Varroa-active dsRNA was recently developed to control Varroa mites within honey bee brood cells. This dsRNA has 372 base pairs that are homologous to a sequence region within the Varroa mite calmodulin gene (cam). The Varroa-active dsRNA also shares a 21-base pair match with monarch butterfly (Danaus plexippus) calmodulin mRNA, raising the possibility of non-target effects if there is environmental exposure. We chronically exposed the entire monarch larval stage to common (Asclepias syriaca) and tropical (Asclepias curassavica) milkweed leaves treated with concentrations of Varroa-active dsRNA that are one- and ten-fold higher than those used to treat honey bee hives. This corresponded to concentrations of 0.025–0.041 and 0.211–0.282 mg/g leaf, respectively. Potassium arsenate and a previously designed monarch-active dsRNA with a 100% base pair match to the monarch v-ATPase A mRNA (leaf concentration was 0.020–0.034 mg/g) were used as positive controls. The Varroa mite and monarch-active dsRNA’s did not cause significant differences in larval mortality, larval or pupal development, pupal weights, or adult eclosion rates when compared to negative controls. Irrespective of control or dsRNA treatment, larvae that consumed approximately 7500 to 10,500-mg milkweed leaf within 10 to 12 days had the highest pupal weights. The lack of mortality and sublethal effects following dietary exposure to dsRNA with 21-base pair and 100% base pair match to mRNAs that correspond to regulatory genes suggest monarch mRNA may be refractory to silencing by dsRNA or monarch dsRNase may degrade dsRNA to a concentration that is insufficient to silence mRNA signaling.

Repellence and larvicidal effects of some selected plant extracts against adult Anopheles arabiensis and Aedes aegypti larvae under laboratory conditions

Insecticides and repellent chemicals are used to control the exposure to disease vectors. In this study, the repellence activity of ethanol extracts of the leaves of spearmint (Mentha spicata) and rosemary (Rosemarinus officinalis) was evaluated against the adult stages of female Anopheles arabiensis. In addition, the larvacidal effect of seed powder of neem (Azadrichiata indica) was evaluated against the 4th instar larvae of Aedes aegypti under laboratory condition. M. spicata caused average percent repellence effects ranging from 95 to 97% at six different concentrations whilst, R. officinalis induced between 63 and 74%. One-way analysis of variance (ANOVA) revealed that there was no significant difference in the repellence effect among the different concentrations of M. spicata extracts used against An. arabiensis (F = 0.848; P = 0.542). In contrast, statistically significant variation in the repellence effects were observed among the different concentrations of ethanolic extracts of R. officinalis against An. arabiensis females (F = 3.609; P = 0.032). The mean percent larval mortality against Ae. aegypti caused by the seed powder of A. indica at a concentration of 5 g/250 mL was 58% at 24 h and 81% at 48 h. There was no significant difference in larval mortality between 24 and 48 h of exposure (t = 2.328; P = 0.145). In conclusion, ethanolic extracts of M. spicata and R. officinalis could be used as potential sources of repellents against An. arabiensis. Besides, A. indica seed powder could be a potential source of larvicides against the larvae of Ae. Aegypti.

Synergistic effect of Lysinibacillus sphaericus and glyphosate on temephos-resistant larvae of Aedes aegypti

BackgroundGlyphosate-based herbicides are one of the most commonly used compounds to control perennial weeds around the world. This compound is very persistent in the environment and tends to filter into aquatic ecosystems, affecting non-target species such as mosquito larvae. Aedes aegypti mosquitoes are vectors of multiple arboviruses such as dengue and Zika. Glyphosate can be degraded into non-harmful environmental compounds by Lysinibacillus sphaericus, a spore forming bacterium which can also kill Ae. aegypti larvae. In this study, we assessed the effect of glyphosate concentrations, typically used in Colombia, on the entomopathogenic activity of L. sphaericus against Ae. aegypti larvae.MethodsBioassays and toxicity curves were performed to compare the larval mortality between different treatments with and without bacteria and glyphosate (Roundup 747®). Larvae were exposed to both bacteria and glyphosate by adding the compound on chloride-free water. Comparisons were made using both probit regression and ANOVA analysis.ResultsANOVA showed a significant difference in larval mortality when adding glyphosate and L. sphaericus at the same time. Thus, a positive synergic effect on larval mortality was found when L. sphaericus and glyphosate were mixed. According to probit analysis, median lethal dose (LD50) for bacterial mixture was of 106.23 UFC/ml and for glyphosate was 2.34 g/l.ConclusionsA positive synergic effect on the mortality of larval Ae. aegypti when exposed to L. sphaericus mixture and glyphosate was found. Molecular studies focusing on the toxin production of L. sphaericus are required to understand more about this synergistic effect.

Effect of aminopyridinium-based ionic liquids against larvae of Culex pipiens (Diptera: Culicidae)

ABSTRACT Culex pipiens is the most abundant mosquito in Al-Madinah Al-Munawwarah region, Saudi Arabia, transmitting several diseases like elephantiasis, avian malaria, and arboviruses. It has become resistant to several insecticides worldwide, and the search for new alternatives should be prioritized. Because of their biological profile and eco-friendly nature, ionic liquids (ILs) have recently attracted the attention of biologists. The present study was carried out to evaluate the effect of six ILs against C. pipiens larvae. Larval mortality, LC50, LC90, LT50 and residual activity of ILS were determined. Aqueous solutions of tested ILs showed up to 100% larval mortality 24 h after exposure. Significant concentration- and time-based differences in larval mortality were found for a given IL as well as between different ILs. Ultimately, the ILs tested in the current study could be arranged in descending order according to their toxicity against larvae as follows: IL7, IL5, IL4, IL1, IL2 and IL6.

Understanding bacterial communities for informed biosecurity and improved larval survival in Pacific oysters

Bacteria are ubiquitous in all marine habitats and can be beneficial or detrimental to the survival and growth of shellfish raised in aquaculture. To reduce the exposure of cultured shellfish to potential pathogens, antibiotics can be used. However, risks associated with this practice have led to the development of alternative techniques such as ultraviolet (UV) light exposure for seawater disinfection. In this study, we used 16S rRNA gene metabarcoding to measure the effect of low (50 mJoules/cm2) and high (200 mJoules/cm2) UV treatment of seawater on the bacterial communities present in hatchery rearing water and in Pacific oyster Crassostrea gigas larvae. 81 samples were collected between 13 and 29 March 2017 for high-throughput DNA sequencing of bacterial communities, including differentially-treated seawater, the microalgae fed to the oysters and oyster larvae (fertilized eggs, early veliger larval stage [D-larvae], and pre-settlement stage) samples. Differences in larval mortality between low and high UV treatments were also assessed. We found that the two UV treatments influenced the overall bacterial community diversity and affected its composition in both seawater and oyster larval samples. While alpha-diversity was mostly driven by the UV treatment, we found that the microbiome composition was primarily affected by temporal changes in the water source. Compared to the bacterial microbiome associated with seawater, the oyster larvae microbiome changed more significantly in response to both UV treatments and sampling dates with marked shifts in the dominant bacteria associated with fertilized eggs (class Gammaproteobacteria, families Rhodospirillaceae and Pelagibacteraceae), the D-larvae (family Alteromonadaceae), and the pre-settlement larvae (families Flavobacteriaceae and Rhodobacteraceae). As larval development progressed, an increasingly complex bacterial community structure was observed. These bacterial community changes were likely driven by multiple factors, including the microbiome associated with microalgal cultures, which increased in complexity over time. Despite the clear response of bacterial communities to both low and high UV treatments, no significant effect was observed in relation to the oyster larval mortality rate. These results suggest that increasing the UV treatment to 200 mJoules/cm2, if required for more efficacious disinfection and biosecurity, would not be detrimental to Pacific oyster larval survival. Further research is required to increase understanding of the dynamics of functionally critical bacterial taxa and their successive roles in post-larval development of Pacific oysters.

Biological responses of midge (Chironomus riparius) and lamprey (Lampetra fluviatilis) larvae in ecotoxicity assessment of PCDD/F-, PCB- and Hg-contaminated river sediments.

We evaluated the utility of chironomid and lamprey larval responses in ecotoxicity assessment of polychlorinated dibenzo-p-dioxins, dibenzofurans (PCDD/F)-, polychlorinated biphenyls (PCB)- and mercury (Hg)-contaminated river sediments. Sediment samples were collected from the River Kymijoki with a known industrial pollution gradient. Sediment for the controls and lamprey larvae were obtained from an uncontaminated river nearby. Contamination levels were verified with sediment and tissue PCDD/F, PCB and Hg analyses. Behaviour of sediment-exposed chironomid and lamprey larvae were measured with Multispecies Freshwater Biomonitor© utilizing quadrupole impedance conversion technique. In addition, mortality, growth and head capsule deformity incidence of chironomids were used as ecotoxicity indicators. WHOPCDD/F+PCB-TEQ in the R. Kymijoki sediments ranged from the highest upstream 22.36ngg(-1) dw to the lowest 1.50ngg(-1) near the river mouth. The sum of PCDD/Fs and PCBs correlated strongly with Hg sediment concentrations, which ranged from <0.01 to 1.15μgg(-1). Lamprey tissue concentrations of PCDD/Fs were two orders and PCBs one order of magnitude higher in the R. Kymijoki compared to the reference. Chironomid growth decreased in contaminated sediments and was negatively related to sediment ∑PCDD/Fs, WHOPCDD/F+PCB-TEQ and Hg. There were no significant differences in larval mortality or chironomid mentum deformity incidence between the sediment exposures. The distinct behavioural patterns of both species indicate overall applicability of behavioural MFB measurements of these species in sediment toxicity bioassays. Chironomids spent less and lampreys more time in locomotion in the most contaminated sediment compared to the reference, albeit statistically significant differences were not detected. Lamprey larvae had also a greater activity range in some of the contaminated sediments than in the reference. High pollutant levels in lamprey indicate risks for biomagnification in the food webs, with potential health risks to humans consuming fish.

Growth of Larval Agrilus planipennis (Coleoptera: Buprestidae) and Fitness of Tetrastichus planipennisi (Hymenoptera: Eulophidae) in Blue Ash (Fraxinus quadrangulata) and Green Ash (F. pennsylvanica).

Emerald ash borer (Agrilus planipennis Fairmaire) is an invasive primary pest of North American ash (Fraxinus spp.) trees. Blue ash (F. quadrangulata) is less susceptible to emerald ash borer infestations in the forest than other species of North American ash. Whereas other studies have examined adult host preferences, we compared the capacity of emerald ash borer larvae reared from emerald ash borer eggs in the field and in the laboratory to survive and grow in blue ash and the more susceptible green ash (F. pennsylvanica). Emerald ash borer larval survivorship was the same on both ash species. Mortality due to wound periderm formation was only observed in living field grown trees, but was low (<4%) in both green and blue ash. No difference in larval mortality in the absence of natural enemies suggests that both green and blue ash can support the development of emerald ash borer. Larvae reared from eggs on blue ash were smaller than on green ash growing in the field and also in bolts that were infested under laboratory conditions. In a laboratory study, parasitism rates of confined Tetrastichus planipennisi were similar on emerald ash borer larvae reared in blue and green ash bolts, as were fitness measures of the parasitoid including brood size, sex ratio, and adult female size. Thus, we postulate that emerald ash borer larvae infesting blue ash could support populations of T. planipennisi and serve as a potential reservoir for this introduced natural enemy after most of the other native ash trees have been killed.

Genetic Structure and Effective Population Size through Time: A Tale on Two Coastal Marine Species with Contrasting Life-History Patterns

Background: Species with planktonic larvae are more likely to show temporal genetic variation, due to differences in larval mortality and dispersal ability. The shanny Lipophrys pholis is a typical benthic rocky intertidal fish with its dispersion limited to a long larval stage. In contrast, the sand smelt Atherina presbyter has a very short planktonic life, small size and weak swimming capabilities, which translates into reduced dispersion potential. Methods: A total of 226 shanny specimens (collected in 2003, 2013 and 2014) and 281 sand smelts (collected in 2005, 2012, 2013 and 2014) were screened for genetic variation using the mitochondrial control region. Genealogies, genetic diversities, temporal structures and contemporary effective population sizes were assessed. Results: Haplotype networks showed deep genealogies with multiple levels of diversification and no temporal structure. Genetic diversity indices showed little variation among sampling periods and were generally high. For L. pholis significant genetic differentiation was detected between 2013 and 2014, while no significant differences were detected between sampling periods in A. presbyter. The shanny showed lower effective population size per generation when compared to the sand smelt (which yielded lack of evidence for genetic drift for the first two periods of the study). Conclusion: These results highlight the fact that temporal changes in the gene pool composition need to be considered when evaluating population structure, especially for species with long pelagic larval dispersion, more vulnerable to fluctuations in the recruitment.

Bacillus thuringiensis efficacy in reducing spruce budworm damage as affected by host tree species

Efficacy of commercial formulations of Bacillus thuringiensis ssp. kurstaki (Btk) against spruce budworm Choristoneura fumiferana in black spruce (Picea mariana (Mill.) BSP), white spruce (P. glauca (Moench) Voss) and balsam fir (Abies balsamea (L.) Mill.) was investigated in Quebec’s Cote-Nord region. As expected, larval mortality was higher in Btk-treated plots (80.26 ± 2.34 %) than in control plots (66.32 ± 2.80 %). There were no differences in larval mortality among the three host tree species tested. Btk was most efficient in reducing spruce budworm defoliation when applied to black spruce and white spruce trees. Black spruce and white spruce exhibited lower final defoliation in Btk-treated plots than balsam fir. Btk applications produced a reduction in defoliation of 36 % in balsam fir, 44 % in white spruce and 41 % in black spruce. Control plots exhibited about 35 % higher amount of current-year foliage destroyed (AFD) and 56 % lower amount of current-year foliage remaining (ARF) than Btk-treated plots, whereas no differences in the amount of current-year foliage produced (AFP) were observed among host tree species. Black spruce trees showed the lowest AFD. Although not statistically significant, black spruce also showed the highest ARF. Our results suggest that Btk application is more efficient in protecting against spruce budworm damage when it is applied to spruce species than it is to balsam fir. It appears that the observed inter-specific differences in host tree foliage protection might be related to interactions between Btk, host tree foliage, and larval feeding behaviour.

Antibiotics influence the toxicity of the delta endotoxins of Bacillus thuringiensis towards the cotton bollworm, Helicoverpa armigera

BackgroundThe cotton bollworm, Helicoverpa armigera is one of the most important crop pests worldwide. It has developed high levels of resistance to synthetic insecticides, and hence, Bacillus thuringiensis (Bt) formulations are used as a safer pesticide and the Bt genes have been deployed in transgenic crops for controlling this pest. There is an apprehension that H. armigera might develop resistance to transgenic crops in future. Therefore, we studied the role of gut microbes by eliminating them with antibiotics in H. armigera larvae on the toxicity of Bt toxins against this pest.ResultsCommercial formulation of Bt (Biolep®) and the pure Cry1Ab and Cry1Ac toxin proteins were evaluated at ED50, LC50, and LC90 dosages against the H. armigera larvae with and without antibiotics (which removed the gut microbes). Lowest H. armigera larval mortality due to Bt formulation and the Bt toxins Cry1Ab and Cry1Ac was recorded in insects reared on diets with 250 and 500 μg ml−1 diet of each of the four antibiotics (gentamicin, penicillin, rifampicin, and streptomycin), while the highest larval mortality was recorded in insects reared on diets without the antibiotics. Mortality of H. armigera larvae fed on diets with Bt formulation and the δ-endotoxins Cry1Ab and Cry1Ac was inversely proportional to the concentration of antibiotics in the artificial diet. Nearly 30% reduction in larval mortality was observed in H. armigera larvae from F1 to F3 generation when the larvae were reared on diets without antibiotics (with gut microbes) and fed on 0.15% Bt or 12 μg Cry1Ab or Cry1Ac ml−1 diet, indicating development of resistance to Bt in the presence of gut microflora. However, there were no differences in larval mortality due to Bt, Cry1Ab or Cry1Ac across generations in insects when they were reared on diets with 250 μg of each antibiotic ml−1 diet (without gut microflora).ConclusionsThe results suggested that antibiotics which eliminated gut microflora influenced the toxicity of Bt towards H. armigera, and any variation in diversity and abundance of gut microflora will have a major bearing on development of resistance to Bt toxins applied as foliar sprays or deployed in transgenic crops for pest management.

Laboratory evaluation of toxicity of &lt;i&gt;Bacillus thuringiensis&lt;/i&gt;, neem oil and methamidophos against &lt;i&gt;Plutella xylostella&lt;/i&gt; L. (Lepidoptera: Plutellidae) larvae

Diamondback moth (DBM), Plutella xylostella (L.), remains a major pest of brassica crops worldwide. Chemical control of this pest remains difficult due to the rapid development of resistance to insecticides and to their effect on natural enemies. The objective of this study was to assess the toxicity of Bacillus thuringiensis (Bt), neem oil and methamidophos on larvae of P. xylostella under laboratory conditions. Leaf-dip bioassay for DBM larvae was used to assess mortality. For each treatment, three doses (low, medium and high) were applied on cabbage leaves and presented to third instar larvae. Larval mortality was performed every 24 hours for a period of eight days. The application of the three dosages of Biobit was more effective against P. xylostella larvae when compared to the other treatments. However, there was no significant difference in larval mortality when all three doses of Biobit were tested compared to the control. Methamidophos was the least toxic treatments with high dosage recording the lowest mortality rate of 52.5%. These results showed that Btbased biopesticides and neem extracts could be of help, but their deployment should be part of an integrated pest management package, which recognizes the constraints of farmers while addressing the requirement to control of P. xylostella populations.Keywords: Diamondback moth, biopesticide, Azadirachta indica, cabbage, bioassay.

Temporal genetic structure in a poecilogonous polychaete: the interplay of developmental mode and environmental stochasticity

BackgroundTemporal variation in the genetic structure of populations can be caused by multiple factors, including natural selection, stochastic environmental variation, migration, or genetic drift. In benthic marine species, the developmental mode of larvae may indicate a possibility for temporal genetic variation: species with dispersive planktonic larvae are expected to be more likely to show temporal genetic variation than species with benthic or brooded non-dispersive larvae, due to differences in larval mortality and dispersal ability. We examined temporal genetic structure in populations of Pygospio elegans, a poecilogonous polychaete with within-species variation in developmental mode. P. elegans produces either planktonic, benthic, or intermediate larvae, varying both among and within populations, providing a within-species test of the generality of a relationship between temporal genetic variation and larval developmental mode.ResultsIn contrast to our expectations, our microsatellite analyses of P. elegans revealed temporal genetic stability in the UK population with planktonic larvae, whereas there was variation indicative of drift in temporal samples of the populations from the Baltic Sea, which have predominantly benthic and intermediate larvae. We also detected temporal variation in relatedness within these populations. A large temporal shift in genetic structure was detected in a population from the Netherlands, having multiple developmental modes. This shift could have been caused by local extiction due to extreme environmental conditions and (re)colonization by planktonic larvae from neighboring populations.ConclusionsIn our study of P. elegans, temporal genetic variation appears to be due to not only larval developmental mode, but also the stochastic environment of adults. Large temporal genetic shifts may be more likely in marine intertidal habitats (e.g. North Sea and Wadden Sea) which are more prone to environmental stochasticity than the sub-tidal Baltic habitats. Sub-tidal and/or brackish (less saline) habitats may support smaller P. elegans populations and these may be more susceptible to the effects of random genetic drift. Moreover, higher frequencies of asexual reproduction and the benthic larval developmental mode in these populations leads to higher relatedness and contributes to drift. Our results indicate that a general relationship between larval developmental mode and temporal genetic variation may not exist.

Foliar terpene chemistry of Pinus pinaster and P. radiata responds differently to Methyl Jasmonate and feeding by larvae of the pine processionary moth

Jasmonic acid and Methyl Jasmonate (MeJA) are important signaling molecules for plant defensive responses upon mechanical wounding, herbivory damage, or fungal inoculation. There is an increased interest in the use of exogenous chemical elicitors such as jasmonic acids to induce natural host defense mechanisms as an alternative to synthetic chemical pesticides. However few studies have compared the response caused by application of elicitors vs. real herbivores and few studies have analyzed the impact on particular pest species of plant responses induced by exogenous application of MeJA. We compared the defensive response of two pine species, one native to our study area (Pinus pinaster) and one introduced (Pinus radiata), after exogenous application of MeJA and after feeding of a regionally important indigenous pest (pine processionary moth, PPM). We analyzed variation in foliar terpenes, nitrogen and water. Additionally we assessed the consequences of plant responses to MeJA for the growth and mortality of PPM larvae. Because the defensive reaction may be influenced by resource availability, we also evaluated effects of site quality on plant responsiveness to MeJA and insect feeding. The exogenous application of MeJa had different effects in the two pine species. In P. radiata, there were no conspicuous increases from MeJA in any measured terpene, and on good sites, there were general decreases in overall concentrations of the three terpene classes. In P. pinaster, MeJA by itself had no detectable effect on overall concentrations of any class of terpenes, but there was a 6-fold increase in the concentration of one monoterpene, linalool. Feeding by PPM induced decreases in terpenes, especially monoterpenes, in both species. Foliar nitrogen contents were markedly higher in P. radiata than P. pinaster – especially on good sites. Foliar water content was similar between pine species and, in both species, was reduced relative to control trees in treatments that included PPM feeding. There were no differences in larval mortality between trees that were and were not exposed to exogenous MeJA. In summary, the exogenous application of MeJA had effects on the terpene chemistry of both pine species, but the effects were less consistent across species and compounds than expected under some models of MeJA biochemistry. It seems likely that operational manipulations of MeJA to manage pests in pine forestry will require further understanding of differences among pine species in their responses to MeJA.

Increased long-flight activity triggered in beet armyworm by larval feeding on diet containing Cry1Ac protoxin.

Evaluating ecological safety and conducting pest risk analysis for transgenic crops are vitally important before their commercial planting. The beet armyworm, Spodoptera exigua, a long-distance migratory insect pest, is not a direct target of transgenic Cry1Ac-expressing cotton in China, but nevertheless it has recently become an important pest. Migrants leaving their natal field arrive in other appropriate habitat far away in a short time, often followed by larval outbreaks. S. exigua has low susceptibility to Cry1Ac. However, our results from laboratory experiments identified (i) sublethal effects of Cry1Ac protoxin on larval development rate, larval and pupal weight, and adult lifetime fecundity, and (ii) increased long-flight behavior triggered by Cry1Ac which may contribute to larval outbreaks elsewhere. No significant differences in larval mortality, pupation rate, adult emergence rate, longevity, pre-oviposition period, or oviposition period were observed between controls and larvae fed on artificial diet incorporating a low concentration of Cry1Ac protoxin. The negative sublethal effects on some developmental and reproductive traits and lack of effect on others suggest they do not contribute to the observed severity of S. exigua outbreaks after feeding on Cry1Ac cotton. Interestingly, the percentage of long fliers increased significantly when larvae were reared on diet containing either of two low-dose treatments of Cry1Ac, suggesting a possible increased propensity to disperse long distances triggered by Cry1Ac. We hypothesize that negative effects on development and reproduction caused by Cry1Ac in the diet are offset by increased flight propensity triggered by the poor food conditions, thereby improving the chances of escaping adverse local conditions before oviposition. Increased long-flight propensity in turn may amplify the area damaged by outbreak populations. This phenomenon might be common in other migratory insect pests receiving sublethal doses of Bt toxins and warrants further study.

Comparison of Morning and Evening Larvicide Applications on Black Fly (Diptera: Simuliidae) Mortality

The downstream movement, or drift, of larval black flies as well as many other aquatic insects has been well documented. This phenomenon has most often been associated with the dusk-to-overnight time frame. Operationally, larvicide applications targeting black flies are typically initiated early in the day and can extend until near sunset. To determine if larvicide applications conducted late in the day would be affected by the drift behavior of larval black flies, 6 larvicide applications were conducted. Three applications were conducted at midmorning and 3 during the evening. Larvicidal applications of Bacillus thuringiensis subsp. israelensis insecticidal proteins targeting Simulium appalachiense demonstrated no difference in larval mortality between morning and evening applications. These findings indicate that the larvae responded in a similar manner to the larvicide during the late morning to early afternoon and evening to night. The drift behavior of larval black flies does not appear to be an impediment to black fly suppression activities.

The diamondback moth, Plutella xylostella, specifically inactivates Mustard Trypsin Inhibitor 2 (MTI2) to overcome host plant defence

The mustard trypsin inhibitor family has so far only been described among cruciferous species which represent the host plants for the specialist diamondback moth (DBM), Plutella xylostella. The performance of a Dutch and Chinese strain of DBM was assessed on transgenic Arabidopsis expressing Mustard Trypsin Inhibitor 2 (MTI2) at a level of 84 μg/g fresh weight equivalent to 12 μM. No significant differences in larval mortality or development were found relative to the control. Trypsin activity in gut extracts from larvae feeding on either control or transgenic plants were titrated with MTI2 and SKTI (Soybean Kunitz Trypsin Inhibitor) to assess the basis of the insensitivity to MTI2. The specific trypsin activity per gut of larvae reared on MTI2 plants was not significantly higher compared to the control, and ca. 80% of trypsin activity could be inhibited by both inhibitors in both treatments, suggesting no specific induction of PI-insensitive activity in response to MTI2 in the diet. On the basis of the apparent equilibrium dissociation constant of Plutella trypsins for MTI2 (80 nM), the gut trypsin concentration (4.8 μM), and the MTI2 concentration in the leaves (12 μM) it was calculated that 99% of the gut trypsin activity sensitive to MTI2 should be inhibited in vivo, unless MTI2 was degraded. Indeed, we found that a pre-incubation of MTI2 and SKTI with gut proteases for 3 h resulted in complete loss of inhibitory activity of MTI2, but not of SKTI, at the concentration ratios found in planta. This process was enzymatic as it was inactivated by heat. Gut extracts of larvae reared on control or MTI2 leaves were equally well capable of this degradation indicating that the inactivating enzymes are constitutively expressed. In conclusion, it appears that the insensitivity of the diamondback moth to MTI2 can be sufficiently explained by the specific degradation of MTI2, thereby protecting itself against this protease inhibitor which is part of the defense of cruciferous plant species.