George O. Poinar

Significance of Achromobacter nematophilus Poinar and Thomas (Achromobacteraceae: Eubacteriales) in the development of the nematode, DD-136 (Neoaplectana sp. Steinernematidae).

By culturing Galleria mellonella, Neoaplectana sp. (DD-136) and Achromobacter nematophilus separately under axenic conditions in the laboratory, it was possible to study the relationship between the bacterium and nematode during nematode parasitism of the insect. The infective-stage juveniles of the nematode were able to penetrate and kill the insect host without the presence of A. nematophilus or any other bacterium. However, without accompanying bacteria the nematode was unable to reproduce. Only when A. nematophilus or a possible replacement, such as Pseudomonas aeruginosa , was added to the blood did reproduction occur. The relationship between A. nematophilus and the nematode is considered a mutualistic one, since the bacterium lives and is protected inside the intestine of the free-living stage of the nematode and is transported and released by the nematode to the haemolymph of a host insect. The nematode, in turn, is dependent on the bacterium for reproduction.

Description and Biology of a New Insect Parasitic Rhabditoid, Heterorhabditis Bacteriophora N. Gen., N. Sp. (Rhabditida; Heterorhabditidae N. Fam.)

The new family, Heterorhabditidae, containing the new genus and species, Heterorhabditis bacteriophora is described. This new species of Rhabditoidea was recovered from Heliothis punctigera Hall (Noctuidae) at Brecon, South Australia. The infective stage juveniles of this nematode carry a specific bacterium in their intestines which is released after the parasites enter the body cavity of a healthy insect. The bacteria kill the insect in 48 hours, and the infective stage juveniles develop into hermaphroditic females that produce young which develop into males and females. The latter mate and produce juveniles that develop into infective stages, which leave the cadaver and search for a new host. H. bacteriophora differs from other nematodes in the Rhabditoidea by possessing a vestigial valve in the basal pharyngeal bulb, a reduced stoma, and dauer stages capable of entering the body cavity of healthy insects. Aside from members of the genus, Neoaplectana, it is the only nematode known to serve as a vector for a bacterial disease of insects. The new species also exhibits heterogony. The nematode described by Pereira (1937) as Rhabditis hambletoni is transferred to the genus Heterorhabditis.

Characteristics of the Specific Bacterium Associated With Heterorhabditis Bacteriophora (Heterorhabditidae: Rhabditida)

The infective stage juveniles of Heterorhabditis bacteriophora Poinar (Heterorhabditidae: Rhabditida) carry a specific bacterium in the lumen of their pharynx and intestine. The bacterial cells are large, motile, peritrichously flagellated, gram negative, non-sporeforming rods. They are released by the infective-stage juveniles after they reach the hemolymph of susceptible insects. Additional cultural and biological characteristics of the specific bacterium are presented.

The ability of Neoaplectana carpocapsae (steinernematidae: Nematodea) to survive extended periods of desiccation

Abstract The gradual desiccation of the agriotos strain of Neoaplectana carpocapsae under laboratory conditions showed the ability of the infective-stage juveniles to survive relative humidities well below the permanent wilting point of plants. More than 90% of the nematodes were living after 12 days at a relative humidity of 79.5%. Even after 4 days exposure to a relative humidity of 48.4%, which corresponds to very dry soil, more than 80% of the nematodes survived. The results suggest that the application of neoaplectanid nematodes to soil is more practical than on exposed above-ground plant parts where they would be subject to rapid and lethal desiccation.

The Presence of Achromobacter Nematophilus in the Infective Stage of a Neoaplectana Sp. (Steinernematidae: Nematoda)

Most infective juveniles of DD-136 (Neoaplectana, Steinernematidae) were found to contain cells of Achromobacter nematophilus Poinar & Thomas in the ventricular portion of their intestinal lumen. In two instances, anterior intestinal cells of the infective juveniles were found to contain bacterial cells, presumably those of A. nematophilus. When the infective stage penetrated into the body cavity of a suitable host, the bacteria were released through the anus and multiplied rapidly in the hosts body, resulting in a fatal septicemia.

Diagnostic manual for the identification of insect pathogens.

Identification of the Groups of Insect Pathogens.- Fungi.- Taxonomic Status.- Life Cycle.- Characteristics of Infected Insects.- Methods of Examination.- Isolation and Cultivation.- Identification.- Testing for Pathogenicity.- Storage.- Literature.- Key to Common Genera.- Bacteria.- Taxonomic Status.- Life Cycle.- Characteristics of Infected Insects.- Factors Affecting Bacterial Infections.- Methods of Examination.- Isolation and Cultivation.- Identification.- Testing for Pathogenicity.- Storage.- Literature.- Key to Common Genera and Species.- Viruses.- Taxonomic Status.- Life Cycle.- Characteristics of Infected Insects.- Methods of Examination.- Isolation.- Identification.- Testing for Pathogenicity.- Storage.- Literature.- Key to Groups of Viruses.- Protozoa.- Taxonomic Status.- Life Cycle.- Characteristics of Infected Insects.- Methods of Examination.- Isolation and Cultivation.- Identification.- Testing for Pathogenicity.- Storage.- Literature.- Key to Common Genera.- Rickettsias.- Taxonomic Status.- Life Cycle.- Characteristics of Infected Insects.- Factors Affecting Natural Infections.- Methods of Examination.- Isolation and Cultivation.- Identification.- Testing for Pathogenicity.- Storage.- Literature.- Key to Genera and Species.- Techniques.- Culture Media, Differential Media, and Ringers Solution.- Bacteriological Tests.- Stains and Staining Procedures.- Miscellaneous Techniques.- Literature Cited.

Amino acid racemization in amber-entombed insects: Implications for DNA preservation

DNA depurination and amino acid racemization take place at similar rates in aqueous solution at neutral pH. This relationship suggests that amino acid racemization may be useful in accessing the extent of DNA chain breakage in ancient biological remains. To test this suggestion, we have investigated the amino acids in insects entombed in fossilized tree resins ranging in age from <100 years to 130 million years. The amino acids present in 40 to 130 million year old amber-entombed insects resemble those in a modern fly and are probably the most ancient, unaltered amino acids found so far on Earth. In comparison to other geochemical environments on the surface of the Earth, the amino acid racemization rate in amber insect inclusions is retarded by a factor of >10(4). These results suggest that in amber insect inclusions DNA depurination rates would also likely be retarded in comparison to aqueous solution measurements, and thus DNA fragments containing many hundreds of base pairs should be preserved. This conclusion is consistent with the reported successful retrieval of DNA sequences from amber-entombed organisms.

Terrestrial Soft-Bodied Protists and Other Microorganisms in Triassic Amber

Protozoa, cyanobacteria, sheathed algae, sheathed fungi, germinating pollen or spores, and fungal spores have been found in amber 220 to 230 million years old. Many of these microorganisms can be assigned to present-day groups. This discovery of terrestrial, soft-bodied protists that can be referred to modern groups indicates that morphological evolution is very gradual in many protists and that both structural and probably functional stasis extend back at least to the Upper Triassic period.

An Upper Eocene Frog from the Dominican Republic and Its Implication for Caribbean Biogeography

A frog of the leptodactylid genus Eleutherodactylus is reported from Eocene amber found in the Dominican Republic. It is the first described amphibian fossil in amber, and the oldest complete lissamphibian fossil from Mesoamerica (Central America and Mexico). Dating of the amber matrix indicates that by the end of the Eocene a diverse fauna was present in the Antilles, much earlier than has generally been proposed. The presence of this and other amber fossils from this same age suggests that Tertiary patterns of landmass movements were significant in determining the present distribution of species.

Ultrastructure of 40-Million-Year-Old Insect Tissue

Examination of the ultrastructure of preserved tissue in the abdomen of a fossil fly (Mycetophilidae: Diptera) entombed in Baltic amber revealed recognizable cell organelles. Structures that corresponded to muscle fibers, nuclei, ribosomes, lipid droplets, endoplasmic reticulum, and mitochondria were identified with the transmission electron microscope. Preservation was attributed to inert dehydration as well as the presence of compounds in the original sap which functioned as natural fixatives. This evidence of cell organelles in fossilized soft tissues represent an extreme form of mummification since Baltic amber is considered to have formed about 40 million years ago.