No-cost meals might not exist for insects feeding on toxic plants

Plants produce chemicals (or plant specialised/secondary metabolites, PSM) to protect themselves against various biological antagonists. Herbivorous insects use plants in two ways: as a food source and as a defence source. Insects can detoxify and sequester PSMs in their bodies as a defence mechanism against predators and pathogens. Here, I review the literature on the cost of PSM detoxification and sequestration in insects. I argue that no-cost meals might not exist for insects feeding on toxic plants and suggest that potential costs could be detected in an ecophysiological framework.

Antioxidant availability trades off with warning signals and toxin sequestration in the large milkweed bug (Oncopeltus fasciatus)

In some aposematic species the conspicuousness of an individual's warning signal and the concentration of its chemical defense are positively correlated. Several mechanisms have been proposed to explain this phenomenon, including resource allocation trade-offs where the same limiting resource is needed to produce both the warning signal and chemical defense. Here, the large milkweed bug (Oncopeltus fasciatus: Heteroptera, Lygaeinae) was used to test whether allocation of antioxidants, that can impart color, trade against their availability to prevent self-damage caused by toxin sequestration. We investigated if (i) the sequestration of cardenolides is associated with costs in the form of changes in oxidative state; and (ii) oxidative state can affect the capacity of individuals to produce warning signals. We reared milkweed bugs on artificial diets with increasing quantities of cardenolides and examined how this affected signal quality (brightness and chroma) across different instars. We then related the expression of warning colors to the quantity of sequestered cardenolides and indicators of oxidative state-oxidative lipid damage (malondialdehyde), and two antioxidants: total superoxide dismutase and total glutathione. Bugs that sequestered more cardenolides had significantly lower levels of the antioxidant glutathione, and bugs with less total glutathione had less luminant orange warning signals and reduced chroma of their black patches compared to bugs with more glutathione. Bugs that sequestered more cardenolides also had reduced red-green chroma of their black patches that was unrelated to oxidative state. Our results give tentative support for a physiological cost of sequestration in milkweed bugs and a mechanistic link between antioxidant availability, sequestration, and warning signals.

Metabolization and sequestration of plant specialized metabolites in insect herbivores: Current and emerging approaches

Herbivorous insects encounter diverse plant specialized metabolites (PSMs) in their diet, that have deterrent, anti-nutritional, or toxic properties. Understanding how they cope with PSMs is crucial to understand their biology, population dynamics, and evolution. This review summarizes current and emerging cutting-edge methods that can be used to characterize the metabolic fate of PSMs, from ingestion to excretion or sequestration. It further emphasizes a workflow that enables not only to study PSM metabolism at different scales, but also to tackle and validate the genetic and biochemical mechanisms involved in PSM resistance by herbivores. This review thus aims at facilitating research on PSM-mediated plant-herbivore interactions.

Dietary cardenolides enhance growth and change the direction of the fecundity-longevity trade-off in milkweed bugs (Heteroptera: Lygaeinae)

Sequestration, that is, the accumulation of plant toxins into body tissues for defense, was predicted to incur physiological costs and may require resistance traits different from those of non-sequestering insects. Alternatively, sequestering species could experience a cost in the absence of toxins due to selection on physiological homeostasis under permanent exposure of sequestered toxins in body tissues. Milkweed bugs (Heteroptera: Lygaeinae) sequester high amounts of plant-derived cardenolides. Although being potent inhibitors of the ubiquitous animal enzyme Na+/K+-ATPase, milkweed bugs can tolerate cardenolides by means of resistant Na+/K+-ATPases. Both adaptations, resistance and sequestration, are ancestral traits of the Lygaeinae. Using four milkweed bug species (Heteroptera: Lygaeidae: Lygaeinae) and the related European firebug (Heteroptera: Pyrrhocoridae: Pyrrhocoris apterus) showing different combinations of the traits "cardenolide resistance" and "cardenolide sequestration," we tested how the two traits affect larval growth upon exposure to dietary cardenolides in an artificial diet system. While cardenolides impaired the growth of P. apterus nymphs neither possessing a resistant Na+/K+-ATPase nor sequestering cardenolides, growth was not affected in the non-sequestering milkweed bug Arocatus longiceps, which possesses a resistant Na+/K+-ATPase. Remarkably, cardenolides increased growth in the sequestering dietary specialists Caenocoris nerii and Oncopeltus fasciatus but not in the sequestering dietary generalist Spilostethus pandurus, which all possess a resistant Na+/K+-ATPase. We furthermore assessed the effect of dietary cardenolides on additional life history parameters, including developmental speed, longevity of adults, and reproductive success in O. fasciatus. Unexpectedly, nymphs under cardenolide exposure developed substantially faster and lived longer as adults. However, fecundity of adults was reduced when maintained on cardenolide-containing diet for their entire lifetime but not when adults were transferred to non-toxic sunflower seeds. We speculate that the resistant Na+/K+-ATPase of milkweed bugs is selected for working optimally in a "toxic environment," that is, when sequestered cardenolides are stored in the body.

Defense of Milkweed Bugs (Heteroptera: Lygaeinae) against Predatory Lacewing Larvae Depends on Structural Differences of Sequestered Cardenolides

Predators and parasitoids regulate insect populations and select defense mechanisms such as the sequestration of plant toxins. Sequestration is common among herbivorous insects, yet how the structural variation of plant toxins affects defenses against predators remains largely unknown. The palearctic milkweed bug Lygaeus equestris (Heteroptera: Lygaeinae) was recently shown to sequester cardenolides from Adonis vernalis (Ranunculaceae), while its relative Horvathiolus superbus also obtains cardenolides but from Digitalis purpurea (Plantaginaceae). Remarkably, toxin sequestration protects both species against insectivorous birds, but only H. superbus gains protection against predatory lacewing larvae. Here, we used a full factorial design to test whether this difference was mediated by the differences in plant chemistry or by the insect species. We raised both species of milkweed bugs on seeds from both species of host plants and carried out predation assays using the larvae of the lacewing Chrysoperla carnea. In addition, we analyzed the toxins sequestered by the bugs via liquid chromatography (HPLC). We found that both insect species gained protection by sequestering cardenolides from D. purpurea but not from A. vernalis. Since the total amount of toxins stored was not different between the plant species in H. superbus and even lower in L. equestris from D. purpurea compared to A. vernalis, the effect is most likely mediated by structural differences of the sequestered toxins. Our findings indicate that predator-prey interactions are highly context-specific and that the host plant choice can affect the levels of protection to various predator types based on structural differences within the same class of chemical compounds.

Fetal Ductus Venosus Pulsatility Index and Diameter during Second and Third Trimester of Gestation

INTRODUCTION

The ductus venosus is a small funnel shaped vessel found posterior to the fetal liver connecting the intra-abdominal umbilical vein and the inferior vena cava. It is one of the three physiological shunts in the fetus. The main objective of this study is to construct the reference table and normogram for fetal ductus venosus Pulsatility Index and diameter with gestational age.

METHODS

This was a prospective cross sectional study conducted during August 2011 to July 2012 taking 294 uncomplicated pregnancies using systemic random sampling method. Three measurements were made for ductus venosus diameter and Pulsatility Index in each fetus during period of fetal quiescence.

RESULTS

The ductus venosus diameter at <20weeks, 20-25 weeks, 25-30 weeks, >30 weeks were 1.16, 1.31, 1.62, 1.81 and Pulsatility Index at <20weeks, 20-25 weeks, 25-30 weeks, >30 weeks were 0.41, 0.44, 0.41 and 0.41 respectively.

CONCLUSIONS

The mean diameter of the ductus venosus was linear across gestational age. The Pulsatility Index shows a scattered distribution across the gestational age.

Antibiotic Use, Its Resistance in Nepal and Recommendations for Action: A Situation Analysis

Antibiotics are crucial, life-saving medicines in the fight against infectious disease, but resistance to these drugs is growing all over. This article presents key findings from a detailed situation analysis produced by the Global Antibiotic Resistance Partnership (GARP)-Nepal working group. In the absence of nationally-representative surveillance, it is not possible to fully describe antibiotic resistance in the country, but many important bacterial pathogens are highly resistant to most first-line and some second-line antibiotics, according to available reports. In credible studies, more than half of Escherichia coli, Klebsiella pneumoniae and Streptococcus pneumoniae isolates tested, and over 30 percent of some Shigella spp. and Vibrio cholerae isolates were resistant to first-line antibiotics. The findings for Neisseria gonorrheae and hospital-acquired Staphylococcus aureus are similar. Antibiotic use in animal food is poorly documented in Nepal, but it is commonly acknowledged to be widespread, contributing to the overall antibiotic resistance burden. The volume of veterinary antibiotic sales in Nepal rose over 50 percent from 2008 to 2012, most through retailers without veterinarian prescription. Antibiotics are necessary to treat infections in animals, but they are also used extensively for preventing disease, a use that can be restricted without jeopardizing animal or human health. They may also be used for promoting animal growth, which can be eliminated with no health consequences. Nepal has made important advances in reducing mortality and morbidity and increasing health coverage, but has not yet taken steps to address antibiotic resistance. The GARP-Nepal working group outlines the components of a national strategy on antibiotic resistance, consistent with the recent call by the World Health Organization for national action plans, to be developed collaboratively with stakeholders and partners from government and all relevant sectors.

Study of enteric fever and antibiogram of Salmonella isolates at a teaching hospital in Kathmandu Valley

Enteric fever is one of the common public health problems in Nepal. This study was carried out at Nepal Medical College Teaching Hospital located at peri-urban area in Kathmandu Valley to find out the prevalence of enteric fever and the sensitivity pattern of the Salmonella isolates. A total of 479 patients with fever were included in the study. Venous blood samples collected aseptically were subjected to culture and were studied following the standard bacteriological procedure. The overall prevalence of enteric fever was 5.4% (26/479). Of them more than half (65.4%) were caused by S. paratryphi A whereas remaining (34.6%) by S. typhi. The positive rate was higher in children aged 1-15 years (8.9%) followed by 15-30 years of age (4.3%) and others (1.9%). Gender wise, females to male ratio was 1.4:1. The occurrence of infections was higher in Dalit (7.1%), Khas (Brahmin and Chhetri) (5.9%) and Madeshi (5.9%) whereas lowest was in Adibasi Janajati (4.8%). Prevalence rate of enteric fever among different sex, age and ethnic group was not significant (p > 0.05). Isolates were highly sensitive to Amikacin (100.0%) and Ciprofloxacin (96.1%) whereas least sensitive to Gentamycin (68.7%).

Asthma symptomatics school children of Sonapur

BACKGROUND

Bronchial asthma is one of the most common illnesses in children. Factors influencing development of asthma have not been studied in rural population.

MATERIALS AND METHODS

Two thousand school-going children from three schools of Sonapur VDC, Sunsari in the surrounding of industries were screened for the presence of symptoms of asthma using a questionnaire suggested by International Study of Asthma and Allergy in Children (ISSAC).

RESULTS

One hundred twenty children were identified with symptoms of bronchial asthma. For each child with asthma two age and sex matched non-asthmatic control were selected from the study population. History, clinical examination and in-depth interview were carried out for all cases and controls. Factors associated with presence of symptoms of asthma on multivariate analysis were: passive smoking (OR 3.33, 95% CI 1.85-7.65), pets at home (OR 5.5, 95% CI 1.04-29.15), and absence of windows in living rooms (OR 4.03, 95% CI 1.17-13.79). Factors such as family history of asthma, history of worm infestation, fuel used for cooking, location of kitchen and food allergy were not significant in statistical analysis.

CONCLUSION

Thus, passive smoking, inadequate ventilation and domestic animals and pets (dogs and cats) at home are significant risk factors associated with presence of symptoms of asthma in these children.

A clinico-epidemiological study of snake bite in Nepal

Envenoming from snake bite is an important medical condition, frequently encountered at the emergency department of BPKIHS hospital (Dharan, Nepal). This is a retrospective study of 52 cases of suspected snake bite who presented at the department from August 1993 to November 1994. Analysis of the data showed that snake bite was more frequent between the ages of 11 to 20 years (36.7%) and 2.5 times more common in males. Fifty-seven per cent of the bites occurred between 1600 h and midnight with highest incidence (51%) occurring during the monsoon (August-October). Twenty per cent of the patients were able to identify the snake species as venomous and 90% of them presented to the hospital within 3 h of being bitten. Sixty per cent of the bites were in the lower limb. Neurotoxicity due to envenoming was recorded in nine patients (17%). No case of coagulopathy was recorded. The overall case fatality was 3.8% but mortality amongst those exhibiting signs of neurotoxicity was 22%.