Janice S. Edgerly

The community ecology of Aedes egg hatching: implications for a mosquito invasion

Abstract. 1. A recently introduced treehole mosquito from Asia, Aedes albopictus, is spreading throughout eastern North America, especially in tyre‐refuse piles. Previous studies have identified inhibitory effects of larvae on egg hatch as a potential population regulatory mechanism within Aedes. Larva‐egg interactions may also occur between species. This experiment assesses the ability of larvae of A. albopictus and two possible competitors in North America, A.triseriatus and A.aegypti, to suppress hatching of conspecific and congeneric eggs.

Phylogeny of embiopterans (Insecta)

A cladistic analysis of embiopterans, based on 157 species (representing 70% of the known genera) and 186 morphological characters, is presented, as well as a molecular analysis for 22 taxa using genes encoding 16S, 18S and 28S rDNA and COI. Species of all known families are included, except Andesembiidae Ross (specimens of which are in a private collection). The evidence presented supports the monophyly of four of the families (Australembiidae, Oligotomidae, Teratembiidae, and Anisembiidae). Notoligotomidae is paraphyletic and included within the Afro‐neotropical family Archembiidae (which is also paraphyletic). The genera Embia, Cleomia, Macrembia, and Dihybocercus (Embiidae) form, together with Australembiidae, a group strongly supported by morphology; the position of the remaining genera of Embiidae has two quite different resolutions. Almost 80% of the genera of Anisembiidae recently described appear as either paraphyletic or polyphyletic. Contrary to the opinion of other specialists, the major groups as well as the monophyly of some families are supported by features which have been ignored in classical approaches to the systematics of Embioptera, such as the ovipositor and cephalic and leg structures, characters with an almost perfect fit.

Characterization of silk spun by the embiopteran, Antipaluria urichi.

Silks are renowned for being lightweight materials with impressive mechanical properties. Though moth and spider silks have received the most study, silk production has evolved in many other arthropods. One insect group that has been little investigated is Embioptera (webspinners). Embiopterans produce silk from unique tarsal spinning structures during all life stages. We characterize the molecular and mechanical properties of Antipaluria urichi (Embioptera) silk through multiple approaches. First, we quantify the number of silk secretory structures on their forelimbs and the tensile properties of Antipaluria silk. Second, we present silk protein (fibroin) transcripts from an embiopteran forelimb protarsomere cDNA library. We describe a fibroin that shares several features with other arthropod silks, including a subrepetitive core region, a non-repetitive carboxyl-terminal sequence, and a composition rich in glycine, alanine, and serine. Despite these shared attributes, embiopteran silk has several different tensile properties compared to previously measured silks. For example, the tensile strength of Antipaluria silk is much lower than that of Bombyx mori silk. We discuss the observed mechanical properties in relation to the fibroin sequence, spinning system, and embiopteran silk use.

Silk Spinning Behavior and Domicile Construction in Webspinners

Analysis of spinning and of silk domiciles revealed similarities and differences for three species of embiids: Antipaluria urichi (Saussure), Pararhagadochir trinitatis (Saussure), and Oligotoma saundersii (Westwood). Each exhibited similar routines while spinning; they positioned the silk by touching the substrate with either front tarsus and by moving the leg to the next position, with many silk strands issuing forth at each step. Reinforced pathways developed as they spun while traveling from diurnal retreats and nocturnal foraging zones. Frass from the interior of their domiciles was spun into the silk. O. saundersii was unique in that it plastered its silk with gathered materials. Analysis of field colonies of P. trinitatis and O. saundersii showed that, like A. urichi, adult females share their silk with offspring and, often, with other females.

The phylogeny and classification of Embioptera (Insecta)

A phylogenetic analysis of the order Embioptera is presented with a revised classification based on results of the analysis. Eighty‐two species of Embioptera are included from all families except Paedembiidae Ross and Embonychidae Navás. Monophyly of each of the eight remaining currently recognized families is tested except Andesembiidae Ross, for which only a single species was included. Nine outgroup taxa are included from Blattaria, Grylloblattaria, Mantodea, Mantophasmatodea, Orthoptera, Phasmida and Plecoptera. Ninety‐six morphological characters were analysed along with DNA sequence data from the five genes 16S rRNA, 18S rRNA, 28S rRNA, cytochrome c oxidase I and histone III. Data were analysed in combined analyses of all data using parsimony and Bayesian optimality criteria, and combined molecular data were analysed using maximum likelihood. Several major conclusions about Embioptera relationships and classification are based on interpretation of these analyses. Of eight families for which monophyly was tested, four were found to be monophyletic under each optimality criterion: Clothodidae Davis, Anisembiidae Davis, Oligotomidae Enderlein and Teratembiidae Krauss. Australembiidae Ross was not recovered as monophyletic in the likelihood analysis in which one Australembia Ross species was recovered in a position distant from other australembiids. This analysis included only molecular data and the topology was not strongly supported. Given this, and because parsimony and the Bayesian analyses recovered a strongly supported clade including all Australembiidae, we regard this family also as monophyletic. Three other families – Notoligotomidae Davis, Archembiidae Ross and Embiidae Burmeister, as historically delimited – were not found to be monophyletic under any optimality criterion. Notoligotomidae is restricted here to include only the genus Notoligotoma Davis with a new family, Ptilocerembiidae Miller and Edgerly, new family, erected to include the genus Ptilocerembia Friederichs. Archembiidae is restricted here to include only the genera Archembia Ross and Calamoclostes Enderlein. The family group name Scelembiidae Ross is resurrected from synonymy with Archembiidae (new status) to include all other genera recently placed in Archembiidae. Embiidae is not demonstrably monophyletic with species currently placed in the family resolved in three separate clades under each optimality criterion. Because taxon sampling is not extensive within this family in this analysis, no changes are made to Embiidae classification. Relationships between families delimited herein are not strongly supported under any optimality criterion with a few exceptions. Either Clothodidae Davis (parsimony) or Australembiidae Ross (Bayesian) is the sister to the remaining Embioptera taxa. The Bayesian analysis includes Australembiidae as the sister to all other Embioptera except Clothididae, suggesting that each of these taxa is a relatively plesiomorphic representatative of the order. Oligotomidae and Teratembiidae are sister groups, and Archembiidae (sensu novum), Ptilocerembiidae, Andesembiidae and Anisembiidae form a monophyletic group under each optimality criterion. Each family is discussed in reference to this analysis, diagnostic combinations and taxon compositions are provided, and a key to families of Embioptera is included.

Is group living an antipredator defense in a facultatively communal webspinner (Embiidina: Clothodidae)?

I tested whether predator attack rate is a function of expanse of silk for colonies ofAntipaluria urichi, a facultatively communal webspinner. The avoidance effect hypothesis predicts that the probability of a predator detecting a group does not increase proportionately with an increase in expanse of silk, and therefore, larger groups are relatively less likely to be attacked. I counted the number of holes inflicted on silk over 3 weeks, an indirect measure of predation, for 47 colonies. Supporting the avoidance effect, holes per perimeter of silk accumulated at a rate lower than would be predicted by size alone. Further analysis using predation risk, computed as holes per individual per silk perimeter, revealed that risk was extremely variable for colonies with little silk (<200 cm) but, on average, did not vary as silk expanse increased. Overall, predators of webspinner colonies appear to be influenced by the avoidance effect, but whether the occupants of the silk are safer is unresolved.

To hatch or not to hatch? Egg hatch response to larval density and to larval contact in a treehole mosquito

Abstract. 1 We investigated the effect on egg hatch of exposure to: (1) varying larval density, and (2) larval contact in Aedes triseriatus Say (Diptera: Culicidae). For 2 days in the laboratory we submerged eggs into a treehole water medium containing 0 (control), 4, 12 or 24 larvae that could either contact the eggs directly or were separated from them by a screen. Following treatment, abundance of microorganisms on the egg surfaces, a food source for newly hatched larvae and a proposed hatching stimulus, was assessed by counts made from serial dilutions of samples. 2 We discovered a complex hatching response to larval contact and to larval density, and an interaction between these two factors in their effect on microbial growth. Hatching was inhibited in the 0‐larva control, even though microorganisms grew abundantly on the eggs. Hatch rate, as well as microbial counts, were high for eggs in direct contact with 4 larvae. As density increased in the larval contact treatment, microorganisms disappeared from the egg surfaces and hatch rate declined. 3 When protected from larval grazing, eggs supported numerous microbial colonies irrespective of larval density. In contrast to the contact treatment group, egg hatch increased with increasing larval density. These observations suggest that the combination of microbial growth and a larval factor stimulates hatch. This hatching response may have evolved because both abundant microorganisms and numerous larvae reflect a habitat of good quality.

Comparison of Embiopteran Silks Reveals Tensile and Structural Similarities across Taxa

Embioptera is a little studied order of widely distributed, but rarely seen, insects. Members of this group, also called embiids or webspinners, all heavily rely on silken tunnels in which they live and reproduce. However, embiids vary in their substrate preferences and these differences may result in divergent silk mechanical properties. Here, we present diameter measurements, tensile tests, and protein secondary structural analyses of silks spun by several embiid species. Despite their diverse habitats and phylogenetic relationships, these species have remarkably similar silk diameters and ultimate stress values. Yet, ultimate strain, Youngs modulus, and toughness vary considerably. To better understand these tensile properties, Fourier transformed infrared spectroscopy was used to quantify secondary structural components. Compared to other arthropod silks, embiid silks are shown to have consistent secondary structures, suggesting that commonality of amino acid sequence motifs and small differences in structural composition can lead to significant changes in tensile properties.

Relating the Cost of Spinning Silk to the Tendency to Share It for Three Embiids with Different Lifestyles (Order Embiidina: Clothodidae, Notoligotomidae, and Australembiidae)

Abstract Although adult female embiids (Order Embiidina) superficially lack morphological diversity, their variety of habitats may impose distinct selective pressures on behavior, such as their use of silk and their tendency to aggregate. For example, where silk serves as a primary defense from environmental threats, coloniality might be adaptive. The cost of production or spinning might also prompt them to share silk. These ideas were tested in laboratory trials involving three species of embiids with different lifestyles: an arboreal species (Antipaluria urichi (Saussure) from a neotropical rain forest, a species (Notoligotoma hardyi (Frederichs) that dwells on surfaces of granite outcrops in Australia, and another Australian species (Australembia incompta Ross) that stitches leaf litter together. The cost of spinning silk was analyzed by recording CO2 output in the short term during spinning and by measuring performance in long-term trials where embiids were forced to repeatedly replace their silk. Their subsequent development or reproductive output was scored. Overall, the cost of spinning was relatively low. However, the tendencies to spin and to aggregate varied in a manner related to how silk is used in the field. As such, the more exposed the embiid is to the elements, as for the two species that spin on surfaces, the more silk they spun and the more likely they settled near a neighbor. In contrast, the embiid that used dead leaves (not silk) as walls for their abodes produced scant silk and showed little tendency to aggregate.

Lichens, Sun, and Fire: A Search for an Embiid-Environment Connection in Australia (Order Embiidina: Australembiidae and Notoligotomidae)

Abstract This investigation is the first to quantify the degree of habitat specialization for any species within the little-known order Embiidina. The lichen and plant communities found in the habitats of two sympatric species, one living on lichens encrusted on granite and another feeding in leaf litter, were characterized using a process of ordination and cluster analysis. Differences among 40 samples and their relationships to environmental factors were probed statistically using Spearman’s coefficient of rank correlations generated by comparing rank similarity matrices of the census sites. The lichen eater, Notoligotoma hardyi (Friederichs), was more abundant in areas with strong southern exposures and was associated with higher lichen abundance. They preferentially grazed on particular lichens, the first indication that an embiid shows specialization in feeding. The detritivore, Australembia incompta Ross, was closely associated with particular plant communities, especially those less susceptible to fire. Their colonies were more common in rockier, coastal areas and less abundant in grasslands and habitats dominated by Eucalyptus. Insight into ecological variation within the order can guide further exploration of other traits (such as silk structure and function and primitive social behavior) in this rarely studied group of insects.