REVISION OF THE HOLARCTIC GENUS PYRACMON (HYMENOPTERA: ICHNEUMONIDAE)

The species of the holarctic genus Pyracmon Holmgren are revised. These are presumably all parasites of soil dwelling larvae of Coleoptera. Pyracmon sepiellum (Holmgren) is a parasite of Macropygon piceus LeConte (Dascillidae) and P. ctenicerae n. sp. is a parasite of Ctenicera destructor (Brown) (Elateridae). Seven species are recognized of which two are described as new, namely bucculentum (Holmgren), fumipenne (Zetterstedt), truncicola Thomson, and heteropus (Thomson), all from Europe, nigrifemur n. sp. from Japan, sepiellum (Holmgren), Holarctic, and ctenicerae n. sp. from western North America. The species are described, keyed, and figured based on characters of the adults. The final instar cephalic structures of larvae of sepiellum and ctenicerae are described and figured, these being the first descriptions representing the genus. Relationships of the genus Pyracmon with other members of the subfamily Campopleginae are discussed.

Some ultrastructural characteristics of mandibular cuticle in an elaterid larva (Coleoptera)

The cuticular walls of the mandibles of larvae of Ctenicera destructor (Brown) have a layer of nonlamellate procuticle with a preferred orientation of cuticular microfibrils and pore canals. This type of cuticle is characteristic of many pterygote adult cuticles but has not been noted in larval cuticles of other cephalic appendages or body sclerites and membranes. This nonlamellate layer is sandwiched between two layers of lamellate procuticle over most but not all of the mandibular base. There is no outer lamellate layer of procuticle in the walls of the mandibular teeth, but the layer of protein epicuticle is exceptionally thick here, comprising about two-thirds of the total wall thickness. These characteristics of the mandibular cuticle are discussed with respect to wall strength, tooth wear, function of mandibular mechanosensilla, and development.

SPATIAL PATTERN AND DENSITY OF CTENICERA DESTRUCTOR AND HYPOLITHUS BICOLOR (COLEOPTERA: ELATERIDAE) IN SOIL IN SPRING WHEAT

Determination of the spatial pattern and estimation of the density of egg, larval, and adult populations of Ctenicera destructor (Brown) and Hypolithus bicolor Eschscholtz were made by soil sampling, and for C. destructor adults, also by cages that collected the emerging adults in the spring. Eggs of both the above species and also those of Aeolus mellillus (Say), which were also found in the samples, were highly aggregated. Small C. destructor larvae were most highly aggregated and medium larvae less so; large larvae were usually randomly distributed. Unlike C. destructor, large H. bicolor larvae were more highly aggregated than either the small or medium bicolor larvae. Sampling by emergence cages showed that C. destructor adults were aggregated while sampling by soil cores showed them to be randomly distributed. The different result obtained by the two methods was attributed to the difference in the size of the sampling unit. Aggregation was detected in 29% of the H. bicolor adult population sampled by soil cores only.Larval densities of C. destructor ranged from a low of 0.25 to a high of 1.46 per sample unit (81 cm2) over the 14-year period that samples were taken; densities of H. bicolor ranged from 0.16 to 0.64. Densities of C. destructor and H. bicolor adults averaged about 6 (range 1–16) % and 12 (0–27) % of the total population of larvae and adults for each respective species. Population composition, in terms of adults and larvae of different sizes, and population fluctuations are discussed.The relation between density and the number of sampling units required to achieve four levels of margin of error at four levels of statistical significance was determined.No satisfactory transformation was found for data of individual samples with a mean less than 1. Several common transformations, including Taylor’s power transformation, were satisfactory for stabilizing the variance of pooled samples.

Ultrastructure and function of digitiform sensilla on the labial palp of a larval elaterid (Coleoptera)

There are typically six elongate pegs positioned in longitudinal grooves in the outer walls of the distal segment of the labial palps of larvae of Ctenicera destructor (Brown). They are termed digitiform sensilla on the basis of their form and function. Each has a subapical pore typical of a contact chemoreceptor in surface scan, and a terminally branched dendrite but not the cuticular pores typical of a chemoreceptive porous hair. The dendritic terminations are encased by the dendritic sheath, the subapical pore is plugged in the wall of the peg, and there is only one innervating neuron, all of which are typical of a tactile mechanoreceptor. These pegs respond electrophysiologically to contact and vibratory stimuli, but not to the amino acids, sugars, salts, and water tested, nor to a changed pressure in the cephalic hemocoel.

Structure of the labial palp of a larval elaterid (Coleoptera) and of sinus cells associated with its sensilla

Within each labial palp of the larval elaterid Ctenicera destructor (Brown) there is a terminal distal lymph sinus that is separated from the hemocoel in the prementum by a cellular mass in the distal two-thirds of the palp. The sensory neurons of the terminal sensilla form two ganglia that extend from the cellular mass into the prementum. Two types of cells intersperse and surround the cells associated with the sensilla. Elongate gobletlike cells, termed hemolymph sinus cells, extend from the hemocoel to the distal lymph sinus within the ganglia and through the cellular mass. Each contains a sinusoid that opens into the distal sinus. Cuboidal cells, termed basal hemolymph cells, are apposed to and interspersed between the bases of the sinus cells. Both types are associated with the basement membrane bounding the hemocoel and seem to transport materials from hemocoel to distal sinus and perhaps also secrete into the latter. Both types of cells may be differentiated hemocytes.

Fine structure of peripheral terminations in the porous sensillar cone of larvae of Ctenicera destructor (Brown) (Coleoptera, Elateridae), and probable fixation artifacts

Nodes occur naturally on the dendritic branches in the receptor-lymph cavity of the antennal sensory cone in larvae of Ctenicera destructor. They increase in number, are often greatly expanded, and may separate from the dendrites as fixation artifacts. Extracellular dictyosomes originate from terminal nodes of the dendritic branches. These dictyosomes secrete vesicles, believed to contain lipoidal substances, directly into the fluid in the receptor cavity. These vesicles either coalesce into large lipoidal globules which produce the peripheral sensory tubules that traverse pores in the covering cuticle, or themselves attach directly to the tubules. The sensory tubules are lipoidal in nature. It is suggested that they serve to conserve moisture in the sensillum and to channel stimulating molecules through the cuticle to the lymph in the receptor cavity. The dendrites are not attached directly to the sensory tubules, but are believed to gain contact with the stimulating molecules through the receptor lymph. The lipoidal substance for sensory tubule secretion is probably transported into the sensory cone by the neurotubules within the dendrites. The results from a technique using glutaraldehyde fixation, ammoniacal silver treatment, and lead staining, without osmium fixation, are described and discussed.

Fine structure of the antennal sensory appendix in the larva of Ctenicera destructor (Brown) (Elateridae: Coleoptera)

The antennal sensory appendix of Ctenicera destructor (Brown) appears to be a compound sensillum basiconicum formed by a union of about 12 individual sensilla. It is innervated by about 36 bipolar sense cells of type I, which occur usually in 12 groups of three neurons each. The sensory cuticle is large, cone-shaped, and abundantly perforated by a slit-tubule system. The dendrites of each group of neurons are enclosed distally by a single tubular cuticular sheath attached to the base of the cone by a suspensory fiber system. The ensheathed portion of the dendrites lies in a receptor-lymph cavity formed by the tormogen and accessory trophic cells. Distal dendritic branches pass below and occasionally enter inner pockets in the sensory cuticle, but no connections were seen between the slit-tubule system and the dendritic surfaces. About 12 of each of four types of cells are associated with the neurons in this sensillum: tormogen, trichogen, accessory trophic, and neurilemma. The ultrastructure and probable function of each type is described. A central, complex junction body region divides each dendrite into morphologically distinct distal and proximal region. All the cells associated with the sensillum are in a compact bundle, which is separated from adjacent sensilla within the antenna by a membranous septum. It is suggested that this sense organ has an olfactory function.

Effect of various fractions of the hot-water extract of germinating rye seed in eliciting biting by larvae of the prairie grain wireworm, Ctenicera destructor Brown

Factors in the hot-water extract of germinating rye seed, which elicit biting responses from larvae of Ctenicera destructor Brown, occurred both in the amino acid fraction and in the carbohydrate fraction of this extract. Factors in the carbohydrate fraction responsible for adding to the activity of the amino acid fraction, when both were recombined, were probably fructose, glucose, and sucrose, although chromatographic separation may have eliminated feeding deterrents. Hot-water extracts of 8-day-old and 11-day-old seedlings of the same rye were considerably less active than that of germinating seed. Plant age differences were suggested to influence the susceptibility and resistance of plants and plant-growth stages to wireworm attack.

Phagostimulatory effects of lipids and related substances on the prairie grain wireworm, Ctenicera destructor Brown

Larvae of Ctenicera destructor Brown bit spots treated with C18 unsaturated fatty acids more often than those treated with other lipids or related substances. They also bit spots treated with 5% solutions of these substances more often than those treated with 1% solutions. The relatively high response recorded for triolein-treated spots may have reflected a metabolic requirement for oleic acid. When spots were treated with mixtures of fatty acids, the larvae bit most frequently those treated with palmitic, oleic, and linoleic acids. These observations support the hypothesis that a phagostimulatory response by insects is not dependent upon the presence of any single substance.

A METHOD FOR SEPARATING THE EGGS OF THE PRAIRIE GRAIN WIREWORM, CTENICERA DESTRUCTOR, FROM SOIL

A technique is described whereby an average of 99% (96–100%) of known numbers of eggs of Ctenicera destructor (Brown) were removed from units of soil 1/2 pint in volume. Average time to process each unit was 11/2 man-hours.