Self-Medication as Adaptive Plasticity: Increased Ingestion of Plant Toxins by Parasitized Caterpillars

Self-medication is a specific therapeutic behavioral change in response to disease or parasitism. The empirical literature on self-medication has so far focused entirely on identifying cases of self-medication in which particular behaviors are linked to therapeutic outcomes. In this study, we frame self-medication in the broader realm of adaptive plasticity, which provides several testable predictions for verifying self-medication and advancing its conceptual significance. First, self-medication behavior should improve the fitness of animals infected by parasites or pathogens. Second, self-medication behavior in the absence of infection should decrease fitness. Third, infection should induce self-medication behavior. The few rigorous studies of self-medication in non-human animals have not used this theoretical framework and thus have not tested fitness costs of self-medication in the absence of disease or parasitism. Here we use manipulative experiments to test these predictions with the foraging behavior of woolly bear caterpillars (Grammia incorrupta; Lepidoptera: Arctiidae) in response to their lethal endoparasites (tachinid flies). Our experiments show that the ingestion of plant toxins called pyrrolizidine alkaloids improves the survival of parasitized caterpillars by conferring resistance against tachinid flies. Consistent with theoretical prediction, excessive ingestion of these toxins reduces the survival of unparasitized caterpillars. Parasitized caterpillars are more likely than unparasitized caterpillars to specifically ingest large amounts of pyrrolizidine alkaloids. This case challenges the conventional view that self-medication behavior is restricted to animals with advanced cognitive abilities, such as primates, and empowers the science of self-medication by placing it in the domain of adaptive plasticity theory

Crop pests and predators exhibit inconsistent responses to surrounding landscape composition

The idea that noncrop habitat enhances pest control and represents a win–win opportunity to conserve biodiversity and bolster yields has emerged as an agroecological paradigm. However, while noncrop habitat in landscapes surrounding farms sometimes benefits pest predators, natural enemy responses remain heterogeneous across studies and effects on pests are inconclusive. The observed heterogeneity in species responses to noncrop habitat may be biological in origin or could result from variation in how habitat and biocontrol are measured. Here, we use a pest-control database encompassing 132 studies and 6,759 sites worldwide to model natural enemy and pest abundances, predation rates, and crop damage as a function of landscape composition. Our results showed that although landscape composition explained significant variation within studies, pest and enemy abundances, predation rates, crop damage, and yields each exhibited different responses across studies, sometimes increasing and sometimes decreasing in landscapes with more noncrop habitat but overall showing no consistent trend. Thus, models that used landscape-composition variables to predict pest-control dynamics demonstrated little potential to explain variation across studies, though prediction did improve when comparing studies with similar crop and landscape features. Overall, our work shows that surrounding noncrop habitat does not consistently improve pest management, meaning habitat conservation may bolster production in some systems and depress yields in others. Future efforts to develop tools that inform farmers when habitat conservation truly represents a win–win would benefit from increased understanding of how landscape effects are modulated by local farm management and the biology of pests and their enemies

Least square mean (±1 SE) of the total amount of the food block eaten by <i>G. incorrupta</i> caterpillars over 5 days in the feeding choice experiment according to parasitism treatment (0–3 <i>E. mella</i> eggs) and post-assay survival to adulthood (survived, died).

<p>Asterisks denote significant differences among means of survivors and victims within each treatment from a Tukey-Kramer test (see text for statistics).</p

Least square mean (±1 SE) of the total amount of the PA block eaten by <i>G. incorrupta</i> caterpillars over 5 days in the feeding choice experiment according to parasitism treatment (0–3 <i>E. mella</i> eggs) and post-assay survival to adulthood (survived, died).

<p>Asterisks denote significant differences among means of survivors and victims within each treatment from a Tukey-Kramer test (see text for statistics).</p

Univariate (ANCOVA) responses of feeding intake by caterpillars in the choice experiment, quantified in terms of i) the angularly transformed percentage of overall intake from the PA block, ii) the log transformed absolute intake of the PA block, and iii) the log transformed absolute intake of the food block over five days.

<p>Significant <i>P</i> values are marked by boldface type.</p

Least square mean (±1 SE) percentage of overall intake from PA block by <i>G. incorrupta</i> caterpillars over 5 days in the feeding choice experiment according to parasitism treatment (0–3 <i>E. mella</i> eggs) and post-assay survival to adulthood (survived, died).

<p>Letters denote significant differences among treatment means from a Tukey-Kramer test (see text for statistics).</p

ANCOVA responses of feeding intake by caterpillars in the choice experiment, quantified in terms of i) the angularly transformed percentage of overall intake from the PA block, ii) the log transformed absolute intake of the PA block, and iii) the log transformed overall intake (PA+food block) over five days.

<p>Significant <i>P</i> values are marked by boldface type.</p

Number of survivors to adulthood of <i>E. mella</i> flies that developed in PA+ and PA− caterpillars.

<p>Parasitoids had lower survival in PA+ caterpillars (see text for statistics).</p

Percentage survival to adulthood of unparasitized and parasitized <i>G. incorrupta</i> caterpillars given a synthetic food lacking (PA−) or containing (PA+) 0.1% monocrotaline.

<p>Survival of unparasitized caterpillars was significantly higher on PA− food, whereas survival of parasitized caterpillars was significantly higher on PA+ food (see text for statistics).</p

Aspects sanitaires du travail des enfants dans les carrieres d’exploitation de gravier et de sable dans la Region Maritime au Togo

Introduction : Le travail des enfants (TDE) est un grave problème de santé publique en raison de ses multiples conséquences. L’Afrique subsaharienne y est particulièrement exposée en raison de la pauvreté.Objectifs : Décrire le profil sociodémographique de ces enfants travailleurs et répertorier les affections liées au travail de ces enfants dans les carrières.Méthodologie : Etude transversale descriptive portant sur les aspects sanitaires du TDE conduite d’août à novembre 2014, sur 18 sites d’extraction de graviers et de sable des préfectures de la région maritime du Togo.Résultats : Nous avons recensé 99 sujets de moins de 18 ans sur une population totale de 345 travailleurs. Les enfants avaient été retrouvés sur tous les sites d’extraction de gravier dans la région maritime.Les enfants étaient dans 77,7% de sexe masculin (77 enfants) avec un sex-ratio 3,3. Tous les enfants avaient au moins 7 ans avec une moyenne de 12 ans et dans 49,5% (49 enfants) leur âge était compris entre 11 et 14 ans.Les accidents de travail ont été signalés dans 81,8% des cas (81 enfants). Les types de lésions rapportées ont été essentiellement des plaies dans 79,8% (79enfants) et des entorses dans 36,4% des cas (36 enfants).Les symptômes respiratoires comme rhume et toux ont été retrouvé dans respectivement 43,4% (43 enfants) et 42,4% (42 enfants) ; des douleurs musculaires étaient retrouvées dans 92,9% des cas.Sur tous les sites visités aucun moyen de protection adapté n’a été observé. La prise en charge des accidents du travail a été effectuée par les enfants eux-mêmes et par leurs parents dans respectivement 46,5% (46 enfants) et 53,5% des cas (53 enfants).Conclusion : Les enfants présents sur tous les sites d’extraction étaient le plus souvent de sexe masculin et avaient un âge moyen de 12 ans. Les pathologies rencontrées sont dominées par les atteintes respiratoires avec les douleurs comme plaintes chez les enfants. Des accidents de travail fréquents sont pris en charge par les enfants ou leurs parents. Mots-clés : Travail des enfants, maladies professionnelles, accidents du travail, carrières, Togo. &nbsp; English Title: Aspects sanitaires du travail des enfants dans les carrières d’exploitation de gravier et de sable dans la Région Maritime au TogoIntroduction: Child labor (CL) is a serious public health problem because of its multiple consequences. Sub-Saharan Africa is particularly vulnerable because of poverty. Objectives: To describe the socio-demographic profile of these child workers and to list the conditions related to the work of these children in careers. Methodology: Cross-sectional descriptive study on the health aspects of the CL conducted from August to November 2014, on 18 gravel and sand extraction sites in the prefectures of the maritime region of Togo. Results: We identified 99 subjects under 18 years old out of a total population of 345 workers. The children had been found at all gravel extraction sites in the Maritime Region. Children were 77.7% male (77 children) with a sex ratio of 3. 3. All children were at least 7 years old with an average of 12 years old and in 49.5% (49 children) their age was between 11 and 14 years old. Work-related accidents were reported in 81.8% of cases (81 children). The types of lesions reported were mainly wounds in 79.8% (79 children) and sprains in 36.4% of the cases (36 children). Respiratory&nbsp; symptoms such as colds and coughs were found in respectively 43.4% (43 children) and 42.4% (42 children); muscle pain was found in 92.9% of cases. At all the sites visited no suitable means of protection were observed. The management of accidents related to work was carried out by the children themselves and their parents in respectively 46.5% (46 children) and 53.5% of the cases (53 children). Conclusion: The children present at all extraction sites were mostly male and had an average age of 12 years. The pathologies encountered are dominated by respiratory disorders with pains as complaints in children. Frequent work accidents are dealt with by children or their parents. Keywords: Child labor, occupational diseases, accidents at work, careers, Togo