Cryptic Larvae Research Articles

UV photoluminescence in lycaenid butterfly larvae and implications for nocturnal monitoring

Abstract Nocturnal ultraviolet (UV) flashlight surveys offer a valuable method for investigating butterfly species with cryptic larvae. Focusing on the Lycaenidae, we address three fundamental questions to inform the design of such surveys and the wider significance of this phenomenon. Do the larvae of all species photoluminesce? Which larval instars photoluminesce and how can this information be used to help determine the optimum timeframe in which to search for larvae in the field? Is the level of photoluminescence in different species affected by the UV wavelength used? Thirteen species of lycaenid butterfly across three subfamilies were tested for photoluminescence in response to UV flashlight. Eight species photoluminesced strongly under 365 nm compared to six under 385–395‐nm UV light. Five species exhibited no photoluminescent response to either wavelength. Neither ova nor pupae of any species tested photoluminesced. Photoluminescence in Satyrium pruni (Black Hairstreak) larvae increased with larval stage under controlled laboratory conditions. A similar effect was found in other species of Theclinae but was initiated at different stages. When monitoring lycaenid larvae, it is recommended that a 365 nm flashlight is trialled first and researchers consider when photoluminesce properties develop in larvae when assessing the optimum timeframe for conducting surveys.

Pattern variation is linked to anti-predator coloration in butterfly larvae.

Prey animals typically try to avoid being detected and/or advertise to would-be predators that they should be avoided. Both anti-predator strategies primarily rely on colour to succeed, but the specific patterning used is also important. While the role of patterning in camouflage is relatively clear, the design features of aposematic patterns are less well understood. Here, we use a comparative approach to investigate how pattern use varies across a phylogeny of 268 species of cryptic and aposematic butterfly larvae, which also vary in social behaviour. We find that longitudinal stripes are used more frequently by cryptic larvae, and that patterns putatively linked to crypsis are more likely to be used by solitary larvae. By contrast, aposematic larvae are more likely to use horizontal bands and spots, but we find no differences in the use of individual pattern elements between solitary and gregarious aposematic species. However, solitary aposematic larvae are more likely to display multiple pattern elements, whereas those with no pattern are more likely to be gregarious. Our study advances our understanding of how pattern variation, coloration and social behaviour covary across lepidopteran larvae, and highlights new questions about how patterning affects larval detectability and predator responses to aposematic prey.

Warning Coloration, Body Size, and the Evolution of Gregarious Behavior in Butterfly Larvae.

AbstractMany species gain antipredator benefits by combining gregarious behavior with warning coloration, yet there is debate over which trait evolves first and which is the secondary adaptive enhancement. Body size can also influence how predators receive aposematic signals and potentially constrain the evolution of gregarious behavior. To our knowledge, the causative links between the evolution of gregariousness, aposematism, and larger body sizes have not been fully resolved. Here, using the most recently resolved butterfly phylogeny and an extensive new dataset of larval traits, we reveal the evolutionary interactions between important traits linked to larval gregariousness. We show that larval gregariousness has arisen many times across butterflies, and aposematism is a likely prerequisite for gregariousness to evolve. We also find that body size may be an important factor for determining the coloration of solitary, but not gregarious, larvae. Additionally, by exposing artificial larvae to wild avian predation, we show that undefended, cryptic larvae are heavily predated when aggregated but benefit from solitariness, whereas the reverse is true for aposematic prey. Our data reinforce the importance of aposematism for gregarious larval survival while identifying new questions about the roles of body size and toxicity in the evolution of grouping behavior.

Cephalic anatomy highlights morphological adaptation to underground habitats in a minute lacewing larva of Dilar (Dilaridae) and conflicting phylogenetic signal in Neuroptera.

Dilaridae are a distinctive and phylogenetically ambiguous neuropteran family. So far, the anatomy of the immature stages remains largely unknown. We examined the 1st instar larvae of Dilar montanus in detail and present results of live observations for the first time. The minute, cryptic larvae display features correlated with their underground lifestyle: for instance, a strongly flattened head, stout antennae, eyelessness, and burrowing forelegs. In contrast to molecular data, several characters suggest a 'dilarid clade' combining Dilaridae with Mantispoidea, for instance a very thin and curved or reduced tentorial bridge, and an elongated postmentum. We found intrinsic antennal muscles and Johnston's organ, the first record of these structures in holometabolous larvae. This proves that the first 2 larval antennomeres are homologous with the scapus and pedicellus. The described characters are discussed and analyzed with an updated matrix of neuropteran larval characters. Alternative scenarios of character evolution are presented. Additionally, we show how the 1st-instar larvae move and feed in the substrate, and also provide a high-resolution video recording of the function of the elongate tubular ovipositor and the egg-laying behavior in an adult female under natural conditions.

Identification of Phyllosoma Larvae of the Lobsters Acantharctus and Biarctus (Crustacea: Scyllaridae) from the SW Indian Ocean.

The accurate assignment of cryptic larvae to species-level is a key aspect of marine ecological research and can be achieved through integrated molecular and morphological studies. A combination of two mitochondrial markers (COI and 16S) and a detailed morphological analysis was used to identify phyllosoma larvae of slipper lobster (Scyllaridae) species collected during a survey in the SW Indian Ocean. Two morphotypes were tentatively assigned to Acantharctus ornatus and Biarctus pumilus, both genera for which the larval morphology was unknown. Morphological revision of an adult specimen used to generate the putative A. ornatus sequences in GenBank revealed that it was misidentified and corresponds to B. dubius. The final phyllosoma stage of B. pumilus and subfinal and final stages of A. ornatus were described, clarifying prior misidentifications in the literature. Scyllarid biodiversity in the SW Indian Ocean is underestimated and sampling of deeper water layers is recommended to complete current knowledge of species and larval stages present in the region.

A Hierarchy of Cues Directs the Foraging of Pieris rapae (Lepidoptera: Pieridae) Larvae.

The foraging patterns of insects reflect a combination of biotic and abiotic constraints. Pieris rapae (L.) (Lepidoptera: Pieridae) larvae exhibit plasticity in their foraging behavior, and their movements in response to flowers, young foliage, light, and gravity were studied. As predicted for palatable cryptic larvae, young instars of P. rapae exhibited predator avoidance behaviors. First- and second-instar larvae fed underneath the leaves where their eggs were oviposited, while late second- and third-instar larvae migrated away from their feeding damage. Using taxis experiments and choice tests, the direction of larval movement was significantly influenced by a hierarchy of three cues. Third-instar larvae exhibited negative gravitaxis, which could be supplanted by positive trophotaxis to young leaves and flowers. The larvae exhibited a significantly greater attraction to the inflorescence than to young foliage. For both the inflorescence and young foliage, visual cues were sufficient to direct larval movement. Understanding the cues that guide larval foraging may lead to more efficient trap crops for pest management.

Diversity, Ecology and Herbivory of Hairstreak Butterflies (Theclinae) Associated with the Velvet Tree,Miconia calvescensin Costa Rica

Larvae of three species of hairstreak butterflies in the subfamily Theclinae (Lepidoptera: Lycaenidae) were found feeding on developing inflorescences, flower buds, and immature fruits of the velvet tree, Miconia calvescens DC. (Myrtales: Melastomataceae) in Costa Rica. Erora opisena (Druce), Parrhasius polibetes (Cramer), and Temecla paron (Godman and Salvin) were studied in association with M. calvescens, an uncommon tree in its natural range in the neotropics and a target for biocontrol as an invader in Pacific islands. Host plant use by the three theclines was similar, with eggs being laid on inflorescences and cryptic larvae remaining there throughout development. Feeding damage by E. opisena was most abundant in pre-flowering M. calvescens, when 23% of inflorescences showed feeding damage characteristic of this species. Feeding damage by T. paron peaked at flowering, when 30% of inflorescences were affected. At field sites, E. opisena and T. paron damaged an average of 26 and 18% of each attacked inflorescence, respectively. In cage experiments, individual third- and fourth-instar larvae of E. opisena damaged an average of 24 and 21% of an inflorescence before pupating, respectively. This study provides the first host plant record for E. opisena and T. paron, the first record of P. polibetes feeding on Melastomataceae, and the first records of E. opisena and T. paron presence in Costa Rica.

Reliable and rapid discrimination of congeneric species by mtDNA SNP analysis by multiplex PCR: application on three Trachurus and two Mullus fish species as model cases

We present a reliable, time-saving, and cost-effective multiplex PCR assay for discriminating congeneric species. Three fish species of the genus Trachurus and two of the genus Mullus served as model cases. Our multiplex PCR method interrogates species-specific diagnostic mitochondrial single nucleotide polymorphisms (mtSNPs). We selected two sets of mtSNPs that are organized in two multiplex systems for the Trachurus and the Mullus species, respectively. In both systems, all individuals tested could be safely assigned to one of the three Trachurus or two Mullus species. This novel SNP typing system offers a convenient and robust DNA profiling system suitable for large-scale identification of commercial fish species, for species with cryptic larvae or during juvenile stages, as well as for wildlife forensics.

Rasgos biológicos y poblacionales del depredador Ceraeochrysa sp. nr. cincta (México) (Neuroptera: Chrysopidae)

Ceraeochrysa sp. nr. cincta (México) (Neuroptera: Chrysopidae) es un depredador con larvas crípticas que atacan diversos artrópodos plaga en frutales de México. Para contribuir al posible aprovechamiento de este insecto benéfico en el control biológico de plagas, esta investigación fue realizada con el objetivo de determinar sus rasgos biológicos y parámetros poblacionales. Los estudios se realizaron bajo condiciones controladas de laboratorio con tres cohortes de 50 individuos de C. sp. nr. cincta. Los resultados mostraron que el tiempo de desarrollo de huevo hasta la emergencia de adultos fue de 29 días, con una supervivencia general de 96%. Los estadísticos demográficos estimados, fueron: Ro = 95, T = 59 días, Td = 8 días y rm= 0.081 hijas/hembra/día. Estos rasgos son similares a los indicados para otras especies de Chrysopidae; en cambio, el porcentaje de hembras fecundadas y fertilidad de huevos fueron menores, y el periodo de preoviposición fue mayor. Estas características reproductivas fueron estudiadas en un experimento subsecuente, donde las hembras permanecieron con diferentes proporciones de machos (1:0, 1:1, 1:2, 1:3 y 1:5) en forma temporal. Excepto por la condición de hembras sin machos (1:0), cuando éstas se mantuvieron en forma temporal con 1, 2, 3 y 5 machos, mostraron un período de preoviposición más corto; también existieron valores altos de hembras en oviposición, fertilidad de huevos y fecundidad. El número de apareamientos bajo las diferentes proporciones de hembras:machos no fue significativamente diferente. Los resultados indican el potencial de C. sp. nr. cincta para ser producida masivamente para su aprovechamiento en el control biológico de plagas en México.

Cryptic estuarine gobiid fish larvae (Pisces: Gobiidae) identified as Pseudogobius olorum using allozyme markers

Allozyme electrophoresis was used to identify cryptic larvae of potentially four sympatric south‐western Australian estuarine gobiid species: Afurcagobius suppositus, Arenigobius bifrenatus, Favonigobius lateralis and Pseudogobius olorum. Genotypes of six diagnostic loci expressed in 46 unidentified larval gobiids indicated that they were unambiguously P. olorum.

Size dependent predation risk in cryptic and conspicuous insects

It is not clear which selective pressures balance the strong fecundity advantage associated with large female body size in insects. A positively size-dependent mortality risk could provide a solution. In aviary experiments with artificial larvae, we studied if larger larvae of folivorous insects are more readily found (= detectability) and/or attacked (= acceptability) by birds. As size and colouration are likely to interact in determining birds’ responses, both cryptic and conspicuous prey items were used. As detectability is likely to be context-dependent, both simple (smooth) and complex (plants) backgrounds were used in respective experiments. In the conspicuous larvae, acceptability correlated negatively with prey size. However, their detectability was context dependent, being positively correlated with size on the simple background, whereas no significant effect was found on the complex background. Surprisingly, cryptic larvae showed no correlation between detectability and size, and there was only a weak tendency for birds to attack large larvae more readily. On the basis of a quantitative model, we conclude that the effect of positively size dependent bird predation, as a single factor, is not likely to counterbalance the fecundity advantage in cryptic species, and may thus not be crucial in determining the optimum for body sizes in these insects. In conspicuous species, there is a potential for different outcomes, because detectability and acceptability affect survival in different directions. The net outcome is, therefore, likely to be highly context-dependent. Furthermore, our results provide an explanation for the recently reported absence of systematic body-size differences between cryptic and conspicuous Lepidopteran larvae: although conspicuous larvae benefit from increasing their warning signal when growing larger, they also suffer a much sharper rise in detectability.

Effect of variation in host size on sex ratio, size, and survival of Syngaster lepidus, a parasitoid of Eucalyptus longhorned beetles (Phoracantha spp.): II

Larvae of the cerambycid beetle Phoracantha recurva Newman colonize the inner bark of stressed or dying Eucalyptus trees. These cryptic larvae are parasitized by the solitary ectoparasitoid Syngaster lepidus Brullé. When denied a choice of host sizes in a previous study, parasitoid females produced only male progeny in 2 week old larvae, but when given access to only large larvae, the sex ratio of the progeny was significantly female biased. When female wasps were simultaneously presented with a range of host sizes in the study presented here, the sex ratio was significantly male biased for wasps produced from the smallest host class (2 weeks old), but was not different among the 3, 4, or 5 week old hosts. The sex ratio of progeny remained constant throughout the life of the ovipositing females. Fertility peaked during the second week of adult life, then declined to zero by the fourth week, with females producing about 22 progeny during their lifetimes. Longevity of females was significantly greater than that of males. Significantly more progeny were produced from 3 week old hosts than from any other age class. There was no difference in the number of progeny emerging from 2 or 4 week old hosts, but significantly fewer progeny were produced from 5 week old hosts. The size of emerging wasps increased with host size for both males and females. In Australia, a complex of parasitoids, uses Phoracantha larvae as hosts. S. lepidus prefers to use younger, smaller larvae, while other members of the parasitoid guild exploit larger larval hosts. The results from this study suggest tradeoffs between sex allocation and percent survival in different host size classes, and reflect the observations from previous field studies of this host–parasitoid complex in Australia.

The effect of host size on the sex ratio of Syngaster lepidus, a parasitoid of Eucalyptus longhorned borers (Phoracantha spp.)

The solitary larval ectoparasitoid, Syngaster lepidus Brullparasitizes the cryptic larvae of two wood-boring beetles, Phora- cantha recurva Newman and Phoracantha semipunctata F. The objective of this study was to determine how the female parasitoids allocated the sex of progeny when presented with larval hosts of uniform size classes. Host size was directly correlated with age of the Phoracantha larval hosts. Groups of Phoracantha larvae of a single age class (2-, 3-, 4-, or 5-week-old) were exposed to par- asitoids, and sex ratios of the resulting parasitoid progeny from each host age class were determined. A significant relationship was observed among the sizes of P. recurva and P. semipunctata hosts and the sex ratio of emerging parasitoids. Parasitized 2-week-old beetle larvae of both Phoracantha spp. produced only male S. lepidus progeny, whereas older larval hosts produced increasing proportions of female parasitoids (up to � 80% females from 5-week-old hosts). Two-week-old Phoracantha larvae of both species produced fewer parasitoids than host larvae 3-5-week-old. The size of parasitoid progeny consistently increased with host larval age (size), and female parasitoids were larger than males across all host size classes. Male S. lepidus developed in approximately 25 days from 2-week-old hosts, and 19-21 days in 3-5-week-old hosts. Female S. lepidus developed in 22-25 days, with developmental time increasing with host size. 2002 Elsevier Science (USA). All rights reserved.

CONTROL OF SPRUCE BUDMOTH, ZEIRAPHERA CANADENSIS MUT. AND FREE., IN WHITE SPRUCE PLANTATIONS WITH ENTOMOPATHOGENIC NEMATODES, STEINERNEMA SPP.

AbstractA spruce budmoth population reduction of 82%, as measured by moth emergence, was realized after a foliar spray in which Futura®, a commercial Bacillus thuringiensis Berliner (B.t.) formulation, was added to a suspension of Steinernema carpocapsae (Weiser). The nematode suspension, which took advantage of the wetting and spreading agents in the formulation, was applied to runoff at the rate of 9785 viable infective juvenile nematodes per litre. Mortality was attributed to the nematodes; B.t. was not available to the cryptic larvae. Soil drench treatments were encouraging, and suggested that applications of nematodes to the soil may be feasible.

Higher survival of an aposematic than of a cryptic form of a distasteful bug.

An experiment was performed to assess the relative survival of two forms of 5th instar larvae of Lygaeus equestris (Heteroptera, Lygaeidae) - the normal red form, called aposematic, and a mutant grey form, called cryptic - when given to hand-raised great tits (Parus major).Sixteen birds were presented with aposematic larvae and 16 were presented with cryptic larvae in 10 consecutive trials. One attack per trial was allowed. Both larval forms were presented against a background matching the grey larvae, but since both prey types were presented in a specific place known to the predator, detection rate for both was assumed to be unity.Birds learned to avoid both prey types. However, the survival of the aposematic larvae was higher than that of the cryptic ones due to three aspects of predator behaviour: i) a greater initial reluctance to attack, ii) a more rapid avoidance learning, and iii) a lower frequency of killing in an attack, when the prey was aposematic. Moreover, a greater number of birds learned to avoid prey without killing any individual, when the prey was aposematic. This result is considered to be due to prey coloration alone, since, in a separate test, no difference in prey distastefulness could be detected.This experiment shows that individual prey can benefit from being aposematic and indicates that individual selection can be a sufficient explanation for the evolution of aposematic coloration. It was concluded that, since the survivorship was 6.4 times higher for the aposematic prey, it could have a detection rate that is correspondingly higher than the cryptic in order for the two forms to have equal fitness.

STUDIES ON THE DERMESTID BEETLE TROGODERMA GRANARIUM EVERTS: ECOLOGY IN MALT STORES

Detailed studies on the environment in malt stores and its effect on the Khapra beetle are described. The observations are correlated with the conclusions from parallel laboratory work.Bulks of malt are stored at 26–69° C. and cooling near their centres is slow. After loading, the distribution of heat is controlled mainly by the position of the kiln, the size of the store and the development of Khapra infestations. Three zones of temperature may be recognized, too hot for Khapra (above 40° C.), favourable (30–40° C.) and too cool for rapid breeding (below 30° C.). Population growth may be progressively retarded by cooling, or heat from the kiln and insect‐heating may allow continuous breeding, although part of the malt may be heated above 40° C., causing migration of the larvae. Some migrants stop in a new favourable zone and others continue into the cool zone, often for a long way.The larva is the most prominent stage in most populations. Throughout population growth, low temperature and the accumulation of faecal pellets cause some larvae to enter diapause and hide either in crevices or on the walls just below the malt surface. After the malt is unloaded, huge numbers of larvae may be hidden and some may survive for more than 4 years. Reloading with new, hot malt stimulates some of the cryptic larvae to emerge, pupate and breed. More larvae emerge from the hottest positions than from elsewhere. The very sharp gradient of humidity in stores does not appear to influence larval behaviour. In contrast to unmalted cereals, malt is too dry to allow a significant upward translocation of moisture above a hot region.Control is very difficult. Current methods involve persistent attack on larvae in empty stores with methyl bromide and contact insecticides, combined with structural improvements. Control by cooling the malt before storage is promising.