Thomas A. Coudron

Characteristics of a developmental arrestant in the venom of the ectoparasitoid wasp Euplectrus comstockii

Parasitic Hymenoptera regulate their hosts in order to provide a suitable source of nutrition and dwelling for their offspring. Few regulatory factors known to cause a specific effect on the host have been structurally characterized. The larval ectoparasitoid Euplectrus comstockii Howard (Hymenoptera: Eulophidae) arrests larval-larval ecdysis in its lepidopteran hosts. Prior to oviposition, the female wasp inject a venom into the hemocoel of the host and that venom alone is effective in causing the arrestment. A venom gland-reservoir structure connected to the lower reproductive tract of the wasp contains a complex mixture of proteins. There are no obvious similarities among the electrophoretic banding pattern (native or denatured) for venom proteins of E comstockii and several other parasitic hymenopteran species. Venomous protein, separated by electrophoretic techniques, with a native mol. wt of c. 66,000, was capable of arresting larval-larval ecdysis in 4th instar larvae of Trichoplusia ni (Lepidoptera: Noctuidae). Nanogram quantities of the protein were sufficient to cause arrestment. The activity of the protein was sensitive to temperature, pH, organic solvent, and protease.

Hydrocarbons in the surface lipids of pupal tobacco budworms, Heliothis virescens

Abstract The surface lipids from pupae of the tobacco budworm, Heliothis virescens, had five homologous series of alkanes. Normal alkanes from 17 to 34 carbon atoms comprised 33% of the alkanes; heptacosane was the major constituent at 11%. Monomethylalkanes comprised 50% of the alkanes and consisted of terminally branched 2- and 3-methylalkanes and internally-branched components. The 9-, 11-, 13-, and 15-methylhentriacontane isomers were the major constituents at 24%. Dimethylalkanes from 33 to 35 carbon atoms comprised 14% of the alkanes. One GLC peak was tentatively identified as a mixture of 11,19- and 13,21-dimethyltritriacontane. Analyses of the hydrocarbons of four strains of pupae showed no difference in the type of hydrocarbons found in the cuticular surface lipids. However, a non-tanning body mutant of one strain did show an increase in the amount of hydrocarbon present. There was no difference in the amount of cuticular surface lipid on diapausing pupae compared with that on non-diapausing pupae. Furthermore, there was no difference in the amount of cuticular surface lipid on male pupae when compared with female pupae in both diapausing and non-diapausing stages of development.

Removing external DNA contamination from arthropod predators destined for molecular gut‐content analysis

Ecological research requires large samples for statistical validity, typically hundreds or thousands of individuals, which are most efficiently gathered by mass‐collecting techniques. For the study of interspecific interactions, molecular gut‐content analysis enables detection of arthropod predation with minimal disruption of community interactions. Field experiments have demonstrated that standard mass‐collection methods, such as sweep netting, vacuum sampling and foliage beating, sometimes lead to contamination of predators with nontarget DNA, thereby compromising resultant gut‐content data. We deliberately contaminated immature Coleomegilla maculata and Podisus maculiventris that had been fed larvae of Leptinotarsa decemlineata by topically applying homogenate of the alternate prey Leptinotarsa juncta. We then attempted to remove contaminating DNA by washing in ethanol or bleach. A 40‐min wash with end‐over‐end rotation in 80% EtOH did not reliably reduce external DNA contamination. Identical treatment with 2.5% commercial bleach removed most externally contaminating DNA without affecting the detectability of the target prey DNA in the gut. Use of this bleaching protocol, perhaps with minor modifications tailored to different predator–prey systems, should reliably eliminate external DNA contamination, thereby alleviating concerns about this possible source of cross‐contamination for mass‐collected arthropod predators destined for molecular gut‐content analysis.

Interaction of Two Bacillus thuringiensis δ-Endotoxins with the Digestive System of Lygus hesperus

The active-toxin form of Cry1Ac (65 kDa) or Cry2Ab was fed to a non-susceptible insect, Lygus hesperus, in an artificial diet. Biochemical and immunocytochemical methods were used to determine the distribution of ingested toxin. The toxins did not elicit a feeding deterrent response. Cry1Ac and Cry2Ab were ingested; small amounts were absorbed into the hemolymph as holoproteins, but most was excreted. SDS-PAGE analysis of Cry1Ac and Cry2Ab incubations with salivary gland homogenate showed a small decrease in the molecular weight of the active toxins. Proteolytic processing of the toxins also occurred in vivo, within the digestive system of L. hesperus. Excreted Cry1Ac and Cry2Ab retained activity toward lepidopteran larvae. Immunocytochemical in vivo localization studies showed negligible association of Cry1Ac with L. hesperus tissues. In contrast, strong extracellular association of Cry2Ab was observed with L. hesperus midgut brush border microvilli and basement membrane, as well as with cellular outlines within the hemolymph and fat body.

Production of Heteropteran Predators

This chapter addresses several key aspects of rearing procedures for predatory bugs. The value of natural, factitious, and artificial foods for the major species used in biological control is reviewed. Whereas several types of factitious foods are routinely used in the production of heteropteran predators, the adoption of artificial diets in mass production systems has remained negligible. Special attention is given to the implications of zoophytophagy for the production of predatory bugs. The use of plants and plant materials as sources of water and supplementary nutrients, and as living and oviposition substrates, is discussed, as well as the potential of alternative substrates. The impacts of crowding, cannibalism, and the presence of microorganisms on the performance of rearing systems are also addressed. Although important gaps in our ability to produce heteropteran predators are identified, equally important is that production will clearly benefit from new technologies that are rapidly expanding our knowledge of genetics and of developmental and reproductive biology.

COMPARISON OF THE HEMOLYMPH PROTEINS IN PERMISSIVE AND NON-PERMISSIVE HOSTS OF EUPLECTRUS COMSTOCKII

Abstract Parasitism by Euplectrus comstockii arrested larval–larval molting in both permissive (e.g. Helicoverpa zea) and non-permissive hosts (e.g. Diatraea grandiosella, Anagasta kuehniella and Ostrinia nubilalis). Parasitized larvae of both permissive and non-permissive hosts manifested a decrease in total weight gain. However, significant alterations of the putative storage proteins occurred only in the permissive host. Therefore, the venom of Euplectrus causes some, but not all, of the same effects in non-permissive hosts as in permissive hosts. Specifically, the ability of the venom to regulate molting was shown to be distinguishable from the ability of the venom to alter the protein titer in the hemolymph of a host. The fact that parasitoid eggs did not hatch on non-permissive hosts indicated that parasitoid development was impacted prior to feeding on the host and the presence of indigenous storage proteins in the non-permissive hosts supports the concept that storage proteins may not be for the direct use by the parasitoid.

Partial morphological and functional characterization of the corpus allatum-corpus cardiacum complex from the two-spotted stinkbug, Perillus bioculatus (Hemiptera: Pentatomidae)

SummarySelected morphological and physiological properties of the corpus allatum (CA)-corpus cardiacum (CC) complex from the two-spotted stinkbug, Perillus bioculatus (Hemiptera: Pentatomidae), were studied. The CAs play an important role in insect physiology because of their production of the juvenile hormones (JHs), i.e., key hormones involved in development and reproduction. We found that the P. bioculatus CA-CC complex is present in two distinct morphological forms, the more frequently observed complex containing one “fused” CA between two CCs and the more rarely observed complex having one CA laterally attached to each CC. These complexes were tested for their ability to synthesize JH-like compounds. We found that the primary lipophilic compound synthesized by the CA-CCs migrated differently from JH III (a JH found in numerous insect species) when subjected to thin-layer chromatography. Furthermore, the synthesis of this compound is stimulated by 2E,6E-farnesol, a known precursor for JH III. These data indicate that the P. bioculatus CA-CC product has chemical properties similar to that of other (as of yet unidentified) hemipteran JHs. In addition, we found that the synthesis of this product is sensitive to pH and buffer type; minimally or not affected by the absence of the CC; expressed at similar levels in days 5–30 postemergent adults; and inhibited or decreased in adults reared under low temperature—short day conditions.

MEDIATED PATHOGENICITY OF THE BACULOVIRUS ACMNPV BY THE VENOM FROM EUPLECTRUS COMSTOCKII HOWARD (HYMENOPTERA : EULOPHIDAE)

The compatibility of the venom from the parasitic species Euplectrus comstockii Howard (Hymenoptera: Eulophidae) with the pathogenicity of Autographa californica (Speyer) (Lepidoptera: Noctuidae) MNPV baculovirus (AcMNPV) was tested in third and fourth instar larvae of Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae). The presence of AcMNPV did not alter the ability of the venom to arrest ecdysis in T. ni larvae. The presence of the venom delayed the rate of viruses by AcMNPV but increased the total mortality rates from days 9 to 14 in both third and fourth instar T. ni larvae. The delay in viruses was minimized by administering the virus prior to envenomation. In the presence of the venom, the final LD50 values were lower for fourth instar larvae than for third instar larvae. Surface response equations were developed to visualize the effect of the venom on the viruses caused by AcMNPV.