Oviposition,larval preference,and larval performance in two polyphagous species: does the larva know best?

It is expected that females preferentially oviposit on plant hosts that allow for optimal larval performance. However, this expectation contradicts empirical evidence where adults do not always choose the best host for their descendants. Recent evidence suggests that females’ host selection depends on the number of potential hosts. Females from oligophagous species seem to be able to choose an appropriate host in terms of larval performance, whereas in polyphagous species, adult oviposition preference is not related with larval performance. This suggests that larvae in polyphagous species could be taking a more active role in host selection than their mothers. Here, we evaluated the oviposition preference and the larval preference and performance of two polyphagous species of economic importance, Copitarsia decolora (Guenée) (Lepidoptera: Noctuidae: Cuculliinae) and Peridroma saucia (Hübner) (Lepidoptera: Noctuidae: Noctuinae), on eight species of cultivated plants. In laboratory and greenhouse choice assays, we tested adult preference for oviposition and larval preference at 1 and 24 h. Larval performance was measured in terms of survival to adulthood, length of larval period, and pupal weight. We found that both adult females and larvae actively choose their hosts and that the larval preference toward the hosts is related to the females’ preference in both herbivore species. However, the females and larvae did not preferentially select the host with the best larval performance, indicating that larval performance is not related to female or larval preference and that other selective pressures are influencing the choice of the host plant in these two species.     

Trade‐offs in oviposition choice? Food‐dependent performance and defence against predators of a herbivorous sawfly

The sawfly Athalia rosae L. (Hymenoptera: Tenthredinidae) is a feeding specialist on plant species of the Brassicaceae, which are characterised by secondary metabolites, called glucosinolates. The larvae can take up the respective glucosinolates of their hosts and concentrate them in their haemolymph to protect themselves against predators. Oviposition preferences of naïve females were tested for three species, Sinapis alba L., Brassica nigra (L.) Koch, and Barbarea stricta Andrz., and were related to larval performance patterns. Larvae were reared on either one of these plants and it was investigated how host‐plant quality influences both the developmental times and growth of larvae (bottom‐up) and the defence efficiency against predators (top‐down). Innately, almost all adult females avoided B. stricta for oviposition and clearly preferred B. nigra over S. alba. On average, larvae developed best on B. nigra. Female larvae reached similar final body masses on all host‐plant species, but males reared on S. alba were slightly lighter. The developmental time of larvae reared on B. stricta was significantly longer than on the other two plants. However, larvae reared on B. stricta were best protected against the predatory wasp Polistes dominulus Christ (Hymenoptera: Vespidae). The wasps rejected these larvae most often, while they attacked larvae reared on S. alba most frequently. Thus, larvae feeding on B. stricta theoretically run a higher risk of predation due to a prolonged developmental time, but in practice they are better protected against predators. Overall, oviposition preferences of A. rosae seem to be more influenced by bottom‐up effects on larval performance than by top‐down effects.     

Does risk of egg parasitism affect choice of oviposition sites by a moth? A field and laboratory study

In many insects the eggs are highly vulnerable and egg parasitism can represent a major cause of mortality. It is thus important for the ovipositing female to find a protected site for her eggs. We have examined how egg parasitation can affect host plant choice by Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae). Ovipositing moths exhibited significantly higher preference for alfalfa compared to cotton, both in the laboratory and the field. However, larval performance, in terms of development rate and the attained larval and pupal weight, was significantly better on cotton than on alfalfa. In laboratory tests no difference in larval survival on the two host plants was observed. To test the hypothesis that seeking enemy-free space could be a factor behind the preference for alfalfa, the parasitation levels on the two plants were investigated. In field tests, the egg parasitoid Chelonus inanitus (Linnaeus) (Hymenoptera: Braconidae) parasitized a significantly higher number of egg batches on cotton than on alfalfa. Furthermore, the parasitoid was significantly faster in finding and parasitizing S. littoralis eggs on cotton than on alfalfa in a cage experiment. These findings support the assumption that the preference for the inferior larval food plant, alfalfa, reflects a search for a host plant species on which attacks by natural enemies are less likely. Possible factors accounting for the preference of S. littoralis for alfalfa and the higher parasitation rates on cotton are discussed.     

Is assessment of oviposition sites using conspecific larval cues a general mechanism in aphidophagous ladybirds (Coccinellidae)?

Aphidophagous ladybirds of the Coccinellinae subfamily are deterred from oviposition in the presence of chemical cues deposited by conspecific larvae, therefore avoiding the detrimental effects of competition and cannibalism to their offspring. However, it is still unknown whether aphidophagous species from other Coccinellidae subfamilies similarly behave. Here, we investigate this question for species of the Scymninae subfamily. A GC‐MS analysis of Scymnus interruptus (Goeze) larval tracks shows that larvae deposit a cocktail of hydrocarbons containing at least five branched‐chain alkanes. Furthermore, our experiments on the oviposition behaviour of S. interruptus and S. nubilus (Mulsant) in the presence of conspecific larval tracks and of conspecific larval wax covering Scymninae larvae show that females do not refrain from ovipositing in the presence of these larval cues. We recommend that more attention is paid to the role of Scymnus spp. in the regulation of aphids because their oviposition strategy might strengthen aphid suppression in agrosystems.     

Is oviposition and larval damage by the leaf-mining fly Calycomyza eupatorivora (Agromyzidae) on its target weed,Chromolaena odorata (Asteraceae), restricted by leaf-quality preferences?

The leaf-mining fly Calycomyza eupatorivora Spencer (Diptera: Agromyzidae) was released in the eastern coastal regions of South Africa for the biological control of the invasive shrub Chromolaena odorata (L.) King and Robinson. Despite widespread establishment, its ability to inflict sufficient foliar damage has been questioned. This laboratory study was initiated to provide some insight into how increasing fly populations (represented by 1, 5 and 10 mating pairs per plant) are likely to influence leaf-mining intensity and the levels of damage. On average, individual plants exposed to five mating pairs displayed significantly more larval mines (248) than those exposed to single pairs (69), while plants exposed to 10 mating pairs were intermediate (125). Similarly, at densities of five mating pairs per plant, the percentages of available leaves that were exploited peaked at 36%, while the percentages of available leaf area that were removed by larval leaf mining peaked at 22%. The non-linear relationship between leaf mining and fly density and the high percentages of unexploited leaves suggest that leaf mining may be influenced by leaf quality, the nature of which is currently unconfirmed. These results also suggest that the levels of leaf exploitation by C. eupatorivora will be too low to have any meaningful impact in the field. Field evaluations, to be reported in a later contribution, have indeed confirmed that the impact of C. eupatorivora on mature populations of C. odorata is negligible.     

Is bioaugmentation a feasible strategy for pollutant removal and site remediation?

Microorganisms can degrade numerous organic pollutants owing to their metabolic machinery and to their capacity to adapt to inhospitable environments. Thus, microorganisms are major players in site remediation. However, their efficiency depends on many factors, including the chemical nature and the concentration of pollutants, their availability to microorganisms, and the physicochemical characteristics of the environment. The capacity of a microbial population to degrade pollutants within an environmental matrix (e.g. soil, sediment, sludge or wastewater) can be enhanced either by stimulation of the indigenous microorganisms by addition of nutrients or electron acceptors (biostimulation) or by the introduction of specific microorganisms to the local population (bioaugmentation). Although it has been practiced in agriculture and in wastewater treatment for years, bioaugmentation is still experimental. Many factors (e.g. predation, competition or sorption) conspire against it. However, several strategies are currently being explored to make bioaugmentation a successful technology in sites that lack significant populations of biodegrading microorganisms. Under optimal local conditions, the rate of pollutant degradation might increase upon addition of an inoculant to remediate a chemical spill; however, the most successful cases of bioaugmentation occur in confined systems, such as bioreactors in which the conditions can be controlled to favour survival and prolonged activity of the exogenous microbial population.     

Biochemical changes involved in stress response and ripening behaviour of γ-irradiated mango fruit

The stress response of ripening mango fruits treated in the pre-climacteric phase with radiation doses of 0.75, 1.25 and 1.75 kGy was investigated. L-Phenylalanine ammonialyase, polyphenol oxidase, peroxidase and catalase activities were determined and significant differences were observed. Differences in the patterns of total phenolics, flavanols and proteins were also observed. Malic enzyme activity was used as an indicator of the ripening stage (climacteric rise, climacteric peak and post-climacteric phase) as well as a measure of the effect of γ-irradiation on fruit ripening. It seems that radiation treatment causes a stress condition in the fruit which, depending on the dose, may lead to browning of the tissue or necrotic decay.     

Host-plant choice and larval growth in the cinnabar moth: do pyrrolizidine alkaloids play a role?

Witte et al. (1992) described two distinct chemotypes of Senecio jacobaea L. Asteraceae, a chemotype with jacobine as one of the major pyrrolizidine alkaloids (PAs) and a chemotype with erucifoline as one of the major PAs. We hypothesized that the presence of erucifoline might be the factor responsible for the lack of success of the cinnabar moth on Senecio erucifolius L. Asteraceae and the S. jacobaea erucifoline chemotype. We performed a survey of the distribution of the two chemotypes in the Netherlands and compared this with the distribution map of Tyria jacobaeae L. Lepidoptera, Arctiidae. The distribution of the two chemotypes in the Netherlands is poorly correlated with the distribution of the cinnabar moth. The jacobine chemotype occurs along the coast and the erucifoline chemotype predominantly inward.An oviposition experiment showed that the cinnabar moth did not discriminate between the two chemotypes of S. jacobaea and S. erucifolius. Larval performance did not differ between the two chemotypes and species. Although the distribution of S. jacobaea jacobine chemotype is loosely associated with the abundance of the cinnabar moth the oviposition and growth experiments indicate that other factors than the presence of erucifoline play a role in this association.The absence of recordings of S. erucifolius as a foodplant for the cinnabar moth might be explained by the phenology of the foodplant. Ovipositing females of the univoltine cinnabar moth prefer flowering plants for oviposition. S. erucifolius starts flowering about 1–2 month later than S. jacobaea just after the peak density of moths.     

Are individuals from thelytokous and arrhenotokous populations equally adept as biocontrol agents? Orientation and host searching behavior of a fruit fly parasitoid

Hymenopteran parasitoids generally reproduce by arrhenotoky, in which males develop from unfertilized eggs and females from fertilized eggs. A minority reproduce by thelytoky, in which all-female broods are derived from unfertilized eggs. Thelytokous populations are potentially of interest for augmentative biological control programs since the exclusive production of females could significantly lower the costs of mass rearing. Behavioral traits are a major component of parasitoid efficacy. Here, we examined orientation and host searching behavior in thelytokous and arrhenotokous populations of the fruit fly parasitoid Odontosema anastrephae Borgmeier (Hymenoptera: Figitidae). Orientation behavior to various odorant sources was studied in a two-choice olfactometer. No major differences were found between thelytokous and arrhenotokous wasps for this behavior. However, when host-searching behaviors were analyzed, some differences were found. Thelytokous females arrived sooner, foraged longer, and remained longer on non-infested guavas than arrhenotokous females. Individuals of both forms exhibited similar stereotyped behavioral sequences vis-à-vis guava treatments, with only slight deviations detected. Our results suggest that individuals from selected thelytokous and arrhenotokous O. anastrephae populations have similar abilities to search for tephritid larvae, supporting the use of thelytokous strains for augmentative releases.     

Can artificially selected phenotypes influence a component of field fitness? Thermal selection and fly performance under thermal extremes

Artificially selected lines are widely used to investigate the genetic basis of quantitative traits and make inferences about evolutionary trajectories. Yet, the relevance of selected traits to field fitness is rarely tested. Here, we assess the relevance of thermal stress resistance artificially selected in the laboratory to one component of field fitness by investigating the likelihood of adult Drosophila melanogaster reaching food bait under different temperatures. Lines resistant to heat reached the bait more often than controls under hot and cold conditions, but less often at intermediate temperatures, suggesting a fitness cost of increased heat resistance but not at temperature extremes. Cold-resistant lines were more common at baits than controls under cold as well as hot field conditions, and there was no cost at intermediate temperatures. One of the replicate heat-resistant lines was caught less often than the others under hot conditions. Direct and correlated patterns of responses in laboratory tests did not fully predict the low performance of the heat selected lines at intermediate temperatures, nor the high performance of the cold selected lines under hot conditions. Therefore, lines selected artificially not only behaved partly as expected based on laboratory assays but also evolved patterns only evident in the field releases.     

Expression and function of aquaporins in human skin: Is aquaporin-3 just a glycerol transporter?

The aquaporins (AQPs) are a family of transmembrane proteins forming water channels. In mammals, water transport through AQPs is important in kidney and other tissues involved in water transport. Some AQPs (aquaglyceroporins) also exhibit glycerol and urea permeability. Skin is the limiting tissue of the body and within skin, the stratum corneum (SC) of the epidermis is the limiting barrier to water loss by evaporation. The aquaglyceroporin AQP3 is abundantly expressed in keratinocytes of mammalian skin epidermis. Mice lacking AQP3 have dry skin and reduced SC hydration. Interestingly, however, results suggested that impaired glycerol, rather than water transport was responsible for this phenotype. In the present work, we examined the overall expression of AQPs in cells from human skin and we reviewed data on the functional role of AQPs in skin, particularly in the epidermis. By RT-PCR on primary cell cultures, we found that up to 6 different AQPs (AQP1, 3, 5, 7, 9 and 10) may be selectively expressed in various cells from human skin. AQP1, 5 are strictly water channels. But in keratinocytes, the major cell type of the epidermis, only the aquaglyceroporins AQP3, 10 were found. To understand the role of aquaglyceroporins in skin, we examined the relevance to human skin of the conclusion, from studies on mice, that skin AQP3 is only important for glycerol transport. In particular, we find a correlation between the absence of AQP3 and intercellular edema in the epidermis in two different experimental models: eczema and hyperplastic epidermis. In conclusion, we suggest that in addition to glycerol, AQP3 may be important for water transport and hydration in human skin epidermis.     

Expression and function of aquaporins in human skin: Is aquaporin-3 just a glycerol transporter?

The aquaporins (AQPs) are a family of transmembrane proteins forming water channels. In mammals, water transport through AQPs is important in kidney and other tissues involved in water transport. Some AQPs (aquaglyceroporins) also exhibit glycerol and urea permeability. Skin is the limiting tissue of the body and within skin, the stratum corneum (SC) of the epidermis is the limiting barrier to water loss by evaporation. The aquaglyceroporin AQP3 is abundantly expressed in keratinocytes of mammalian skin epidermis. Mice lacking AQP3 have dry skin and reduced SC hydration. Interestingly, however, results suggested that impaired glycerol, rather than water transport was responsible for this phenotype. In the present work, we examined the overall expression of AQPs in cells from human skin and we reviewed data on the functional role of AQPs in skin, particularly in the epidermis. By RT-PCR on primary cell cultures, we found that up to 6 different AQPs (AQP1, 3, 5, 7, 9 and 10) may be selectively expressed in various cells from human skin. AQP1, 5 are strictly water channels. But in keratinocytes, the major cell type of the epidermis, only the aquaglyceroporins AQP3, 10 were found. To understand the role of aquaglyceroporins in skin, we examined the relevance to human skin of the conclusion, from studies on mice, that skin AQP3 is only important for glycerol transport. In particular, we find a correlation between the absence of AQP3 and intercellular edema in the epidermis in two different experimental models: eczema and hyperplastic epidermis. In conclusion, we suggest that in addition to glycerol, AQP3 may be important for water transport and hydration in human skin epidermis.     

Sex-dependent effects of larval food stress on adult performance under semi-natural conditions: only a matter of size?

Organisms with complex life-cycles acquire essential nutrients as juveniles, and hence even a short-term food stress during development can impose serious fitness costs apparent in adults. We used the Glanville fritillary butterfly to investigate the effects of larval food stress on adult performance under semi-natural conditions in a population enclosure. We were specifically interested in whether the negative effects observed were due to body mass reduction only or whether additional effects unrelated to pupal mass were evident. The two sexes responded differently to the larval food stress. In females, larval food stress reduced pupal mass and reproductive performance. The reduced reproductive performance was partially mediated by pupal mass reduction. Food stressed females also had reduced within-patch mobility, and this effect was not dependent on pupal mass. Conversely, food stress had no effect on male pupal mass, suggesting a full compensation via prolonged development time. Nonetheless, food stressed males were less likely to sire any eggs, potentially due to changes in their territorial behavior, as indicated by food stress also increasing male within-patch mobility (i.e., patrolling behavior). When males did sire eggs, the offspring number and viability were unaffected by male food stress treatment. Viability was in general higher for offspring sired by lighter males. Our study highlights how compensatory mechanisms after larval food stress can act in a sex-specific manner and that the alteration in body mass is only partially responsible for the reduced adult performance observed.     

The effect of height on earnings: Is stature just a proxy for cognitive and non-cognitive skills?

While taller workers are regularly observed to earn more, there is debate concerning the independent contribution of stature to labor earnings. This study investigates the degree to which the association of height and earnings in Pakistan is independent of other cognitive and socio-emotional skills. Next, the relationship between height and earnings is explored when measures of cognitive ability and an index of socio-emotional capacity are included separately. The paper finds only a modest attenuation in the contribution of height to earnings after controlling for additional dimensions of human capital, suggesting that height provides independent information on labor productivity. This result is robust to treating height as endogenous. The paper also examines non-linearities in the relationship between height and earnings. In contrast to results from relatively few other contributions to research on this non-linear relationship, height is associated with earnings only when an individual is taller than the median height. This lends some support to the role of status and confidence in the yet unresolved question as to the relative contribution of direct and indirect influence of height on earnings.     

Is escaping deer browse just a matter of time in Picea sitchensis? A chemical and dendroecological approach

We combined chemical and dendroecological analyses to understand the mechanisms that are involved in escaping deer browse by young Sitka spruce (Picea sitchensis) exposed to browsing by Sitka black-tailed deer (Odocoileus hemionus sitchensis) on Haida Gwaii (British Columbia, Canada). We compared chemical defences (terpenes), nutritive compounds (nitrogen, non-structural constituents, cellulose, and lignin), as well as age and radial growth of two young spruce categories growing side by side: (1) stunted spruces that were heavily browsed, shorter than the browse line, and (2) escaped spruces that were taller than the browse line but still browsed below the browse line. Escaped and stunted spruces did not differ in terpene concentrations, or in nutritive compound contents, suggesting that they had similar palatability. Escaped spruces were older that stunted spruces. Stunted and escaped trees had similar slow growth when young, suggesting no difference in initial browsing between the two spruce categories. For escaped spruce, there was a dramatic increase in radial growth at about 12-13 years old, suggesting that the apex of the trees had escaped deer browse. Because the two categories of spruces were equally accessible and did not differ in chemical defences or in nutritive compounds, and because escaped spruces were older than stunted trees and had a similar slow radial growth in their first 12-13 years, we conclude that morphological differences between stunted and escaped browsed trees are due to age and that it is only a matter of time before spruce escape deer on Haida Gwaii.     

Is the remodeling of the polyp prepattern in a hydrozoan planula a function of larval age or size and is it of “adaptive” significance?

Eggs of medusae develop into lecithotrophic planulae that undergo metamorphosis at different ages to form polyps. As planulae age they decrease in size as their yolk stores are utilized. The planulae of most Phialidium medusae develop into polyps where there is a decrease in the size of the holdfast region and a relative increase in the size of the hydranth region as they age. These changes occur independently of the decrease in planula size. In planulae with a decrease in the size of the holdfast region and an increase in the size of the hydranth-forming region there was a 50% decline in polyps that successfully stayed attached to the substrate after metamorphosis. These aged planulae produced an initial hydranth with the same number of tentacles as polyps from full-sized young planulae while young half-sized planulae produced hydranths where the tentacle number was smaller. The first phase of polyp colony growth with a small initial hydranth was slower than growth of a colony with a larger initial hydranth. Predation during this period led to more death in colonies with a small initial hydranth. The decline in successful attachment in aged planulae was not offset by the higher rate of growth and a smaller window of time where predation leads to death, suggesting that this age-related developmental change in planulae was not adaptive.     

Is the marginal otolith increment width a reliable recent growth index for larval and juvenile herring?

Marginal otolith increment width analysis was performed on field‐collected larval and juvenile spring‐spawned herring Clupea harengus that experienced variable feeding conditions and high temperatures that were above the optimum for growth. Although drastic zooplankton biomass reduction had a significant effect on increment width, a delay of a few days in the otolith response was observed. More importantly, a very clear, positive temperature effect on marginal increment width was demonstrated in fish characterized by temperature independent somatic growth. These results indicate that under natural conditions it may be impossible to distinguish increment width changes related to variation in feeding conditions from changes caused by temperature fluctuations. Therefore, it was concluded that marginal otolith increment width analysis could not be used as a recent growth index ( I _G) for herring larvae and juveniles exposed to drastic temperature fluctuations. The implication of these results is significant not only for the use of marginal increments as a recent growth index, but also if growth rate backcalculation is to be used as a research method.