Pyrrolizidine alkaloids on three trophic levels – evidence for toxic and deterrent effects on phytophages and predators

Summary. Pyrrolizidine alkaloids (PAs) present a model system in the investigation of tritrophic interactions mediated by plant secondary compounds. However, their toxicity for insect herbivores has never been experimentally proven. Here, we demonstrate the toxic effects of a PA on growth and survival of the eri silk moth Philosamia ricini. In a feeding experiment, larvae of this generalist herbivore fed with an artificial PA diet gained weight significantly slower than control animals, and died as pupae. We suggest that derivatives of the ingested PA N-oxide damage developmental functions during metamorphosis. A tracer test with [¹⁴C]senecionine N-oxide revealed that the caterpillars lack adaptations that would prevent conversion of the chemical into the pro-toxic free base. In contrast, the PA adapted leaf beetle Longitarsus anchusae accumulates PAs as N-oxides. We tested the purpose of sequestration in this species as defence against predators. Through a series of prey choice experiments with three carabid predator species, chemically non-protected bark beetle pupae were chosen almost uniformly over L. anchusae pupae. In a following choice test with one of these predators, artificially PA-treated mealworm segments deterred the predator from feeding. Overall the study corroborates the immediate toxic effect of PAs on non-adapted herbivores and the protective effect that adapted insects may gain by sequestering them. It thereby underlines the potential for PAs to play a central role in multitrophic interactions between plants, phytophages and their predators.     

Determination of atrazine in rainfall and surface water by enzyme immunoassay

Rainwater and surface water from four sites in Germany (Bavaria and Lower Saxony) were analyzed for atrazine by enzyme immunoassay from June 1990 until October 1992. The limit of quantification of the immunoassay was 0.02 μg/L with a middle of the test at 0.2 μg/L. About 60 % of the samples contained measurable amounts of atrazine. Seasonal trends were observed, with the highest concentration in the summer months of up to 4 μg/L for rainwater and up to 15 μg/L for surface waters. The highest concentrations were found in agricultural areas, while in the investigated national parks up to 0.56 μg/L could be detected in rain water. This points to long-range atmospheric transport from agricultural areas to pristine national parks. Samples from forest stands usually showed higher atrazine concentrations than samples from open fields. Deposition rates of 10 – 50 μg/m² · yr were observed in the national parks and 10–180 μg/m² · yr at the agricultural sites. Comparison of results obtained by enzyme immunoassay and GC/MS showed a good correlation of r = 0.95.     

The transformation of outdoor ammonium nitrate aerosols in the indoor environment

Recent studies associate particulate air pollution with adverse health effects; however, the exposure to indoor particles of outdoor origin is not well characterized, particularly for individual chemical species. We conducted a field study in an unoccupied, single-story residence in Clovis, California to provide data and analyses to address issues important for assessing exposure. We used real-time particle monitors both outdoors and indoors to quantify nitrate, sulfate, and carbon particulate matter of particle size 2.5 μm or less in diameter (PM-2.5). The results show that measured indoor ammonium nitrate concentrations were significantly lower than would be expected based solely on penetration and deposition losses. The additional reduction can be attributed to the transformation indoors of ammonium nitrate into ammonia and nitric acid gases, which are subsequently lost by deposition and sorption to indoor surfaces. A mass balance model that accounts for the kinetics of ammonium nitrate evaporation was able to reproduce measured indoor ammonium nitrate and nitric acid concentrations, resulting in a fitted value of the deposition velocity for nitric acid of 0.56 cm s⁻¹. The results indicate that indoor exposure to outdoor ammonium nitrate in Central Valley of California are small, and suggest that exposure assessments based on total particle mass measured outdoors may obscure the actual causal relationships for indoor exposure to particles of outdoor origin.     

Pleasure in using adaptive cruise control: A questionnaire study in The Netherlands

Objective: Adaptive cruise control (ACC), a technology that allows for automated car following, is becoming increasingly prevalent. Previous surveys have shown that drivers generally regard ACC as pleasant but that they have to intervene when the ACC reaches its operational limits. The former research has been mostly concerned with specific car brands and does not fully reflect the diversity of ACC types in traffic today. The objective of the present research was to establish the determinants of pleasure in using ACC.

Methods: A 55-item online questionnaire was completed by Dutch users of diverse ACC systems.

Results: Respondents (N = 182) rated their ACC highly, with a mean score of 8.0 on a scale from 1 (extraordinarily negative) to 10 (extraordinarily positive) and were most pleased with ACC on high-speed roads and in low-density traffic. Moreover, the findings point to specific operational limits such as associated with cut-in situations. Pleasure was greater for the types of ACC that are able to decelerate to a full stop, according to 48% of our sample. An analysis of the free-response items indicated that respondents who were displeased with ACC mentioned its occasional clumsiness and the dangerous situations it may evoke, whereas those who were pleased with ACC valued the complementarity of human and machine and emphasized the roles of responsibility and experience in using ACC.

Conclusion: Pleasure in using ACC is a function of both technological advances and human factors.     

Nutritional correlates and mate acquisition role of multiple sexual traits in male collared flycatchers

The information content of a sexual signal may predict its importance in a multiple signal system. Many studies have correlated sexual signal expression with the absolute levels of nutrient reserves. In contrast, the changes of nutrient reserves associated with signal expression are largely unknown in the wild due to technical limitations although they are important determinants of signal information content. We compared two visual and eight acoustic sexual traits in male collared flycatchers to see whether the nutritional correlates of expression predict the role of the signal in sexual selection. We used single point assays of plasma lipid metabolites to estimate short-term changes in nutritional state in relation to sexual trait expression during courtship. As a measure of sexual selection, we estimated the relationship with pairing latency after arrival in a 4-year dataset. Males which found a mate rapidly were characterized by large wing and forehead patches, but small song strophe complexity and small figure repertoire size. Traits more strongly related to pairing latency were also more closely related to changes in nutrient reserves. This indicates a link between signal role and information content. Small wing patches and, surprisingly, complex songs seemed to indicate poor phenotypic quality and were apparently disfavoured at mate acquisition in our population. Future studies of the information content of sexual traits, especially dynamic traits such as song, may benefit from the use of plasma metabolite profiles as non-invasive indicators of short-term changes in body condition.     

Quantitative analysis of pyrrolizidine alkaloids sequestered from diverse host plants in Longitarsus flea beetles (Coleoptera, Chrysomelidae)

Summary. Several species of the flea beetles genus Longitarsus are able to sequester pyrrolizidine alkaloids (PAs) from their host plants. In five Longitarsus species we compare the concentration of PAs present in their host plants belonging to the Asteraceae or Boraginaceae with those found in the beetles. To get an estimate of the intrapopulation variability, three samples of five beetles each and five individual plants were analyzed for each comparison. A strong intrapopulation variability could be detected both among plant and beetle samples. The total concentration found in the beetles varied strongly between species. The local host plant and its phenology influence the concentrations present in the beetles as evidenced in comparisons of a single beetle species from two different hosts and of one beetle species collected at the same site at different times of the year. In addition, different beetle species apparently vary in their capacity to sequester the alkaloids, at the lowest extreme the mean PA concentration in the beetles (0.034 μg PA/mg dry weight) was 1/30 of the mean concentration found in the plant leaves (L. aeruginosus from Eupatorium cannabinum), at the highest extreme (2.098 μg PA/mg dw) the concentration in the beetles was a 1000 fold higher than in the plant leaves (L. nasturtii from Symphytum officinale). The highest mean concentration found in the beetles was 3.446 μg/mg dw (L. exoletus from Cynoglossum officinale). The absolute concentrations found in the beetles are comparable to other insects which have been shown to be effectively defended against their potential predators. Received 22 June 1999; accepted 25 August 1999     

Mikrobieller PAK-Abbau

The biodegradation of the five ring PAH benzo[a]pyrene (BaP) is assumed to be limited by the low water solubility of this compound. A mixed culture of microorganisms — isolated from a PAH-contaminated soil — was able to degrade¹⁴C labelled BaP in mineral medium by cometabolism with phenanthrene, fluoranthene, anthracene and pyrene as sources of carbon and energy. The mineralisation of these compounds to low levels resulted in an inhibition of the degradation of BaP. After the new addition of the four PAH compounds to the culture medium the mineralisation of BaP started again. A non-ionic surfactant of the alkylpolyglycoside type (Plantacare 2000 UP) increased the concentration of BaP in the culture medium because of solubilization. At high Plantacare concentrations, the degradation of BaP was completely inhibited above the critical micelle concentration (cmc). The degradation of the three and four ring PAHs was also inhibited. If the surfactant was metabolised to concentrations below the cmc, an increase of mineralisation of BaP could occur up to 24% in 384 days.     

Health and population-dependent effects of ocean acidification on the marine isopod Idotea balthica

Three populations of the grazing isopod Idotea balthica were exposed to high CO₂ treatment for a period of 20 days to investigate the effect of ocean acidification (OA) on animal health and immunocompetence. The results of the populations from more saline habitats were comparable and showed a 60–80 % decrease in immune response as a result of the high CO₂ treatment. Analysis of protein carbonyls showed no treatment effect, indicating that short-term OA does not increase oxidative protein damage. Meanwhile, the third tested population from the lower saline Baltic Sea had higher background protein carbonyl levels. Ocean acidification in addition to this resulted in 100 % mortality. The results of this study show that OA reduced immunocompetence of this marine isopod. In addition, populations and individuals in poor health are potentially at greater risk to succumb under OA.     

Amphibian myiasis. Blowfly larvae (Lucilia bufonivora,Diptera: Calliphoridae) coping with the poisonous skin secretion of the common toad (Bufo bufo)

The blowfly Lucilia bufonivora shows high host specificity for toads despite the host’s toxic skin secretion, which consists mainly of bufadienolides. These toxins are effective blockers of the Na⁺, K⁺-ATPase, an enzyme that is essential for many physiological processes in animals. Whereas common toad (Bufo bufo) toxins were identified in the larvae of the fly, few toxins were found in the pupae and empty puparia as trace amounts, while adult flies were entirely free of these toxic compounds. Similar results were obtained when larvae of generalist necrophagous blowflies (L. sericata, Calliphora vicina) fed on toad carcasses. Analysis of the Na⁺, K⁺-ATPase gene revealed no amino acid substitution at positions known to mediate resistance to bufadienolides in other systems. Alternative mechanisms of resistance such as efficient excretion of the compounds may enable the flies to use this poisonous food source.