Insect Pathology

1. Insect Pathology Prof. Abdelwahab A. Ibrahim Entomology Department, Faculty of Science, Benha University

2. Prof. Abdelwahab A. Ibrahim BACTERIA • Bacteria are prokaryotes, They have a cell wall. no well-defined nucleus or organelles. • Bacterial pathogens are classified according to many factors such as infective dose, site of infection, host range and mode of action. • Insect bacterial pathogens includes two main groups Spore formers and non-spore formers. • Spore forming bacteria which may be: Obligate: - Grow and divide only inside the insect host as: - e.g. Bacillus popilliae and B. lentimorbus (causing milky disease in Japanese beetles) - e.g. Clostridium malacosomateand C. brevifaciens. Facultative: - Can grow easily in Petri dishes or in liquid culture but need specific conditions. for spore formation in artificial media. - It can be divided into 2 groups: - Crystalliferous : It can form protein crystals toxic to insect larvae as B. thuringiensis - Non- Crystalliferous: It form spores but no crystals as B. cereus. • NonSporeforming bacteria which may be: - Facultative as Serratiamarcescens - Potential pathogens as Pseudomonas, Aerobacter, and Proteus.

3. Prof. Abdelwahab A. Ibrahim BACTERIA • The most common bacterial flora found in digestive tracts of healthy insects are gram-negative small rods, resemble the flora of higher animals. Many of these bacteria are saprophytes; others are obligate anaerobes.. • The bacteria, in different insect species, may range from very small to rods to large spirochete-like forms. Some of these bacteria are intimately attached to the midgut epithelium and chitinous wall of the hindgut. Adult insects pass some bacteria from generation to generation in association with the eggs. Diseases caused by some spore forming bacteria: • The most important bacteria causing diseases are the spore forming bacteria which have dormant stage resisting environmental conditions outside the host. • Family Bacillaceae contains two important genus causing insect diseases: Genus Bacillus (aerobic or facultative aerobics). Genus Clostridium (anaerobic or aero-tolerant).

4. Prof. Abdelwahab A. Ibrahim BACTERIA • Pathogens of Genus Bacillus • Bacteria of genus Bacillus are able to form endospores and can secrete enzymes that analyze the cell walls of host during growth (exo-enzymes) • They are aerobic, unicellular, usually bacilliform, spore forming bacteria. • Infection occurs after ingestion of bacterial cells or spores. They mainly affect phytophagous larval stages. • Bacillus spp can be easily produced by fermentation. P. japonica) larvae

5. Prof. Abdelwahab A. Ibrahim BACTERIA • Bacillus thuringiensis • During sporulation this bacteria produces a large proteinaceous crystal (parasporal body or ẟ- endotoxins) which is bipyramidal in shape and also a thick walled endospore. The crystal is an endotoxin which dissolves inside the host in alkaline gut fluids and releases toxic polypeptides. • This genus was described by Berliner 1911, and contains several serotypes, most of them are pathogenic to Lepidoptera larvae. • B. thuringiensis serotype H-14 is highly pathogenic to mosquito larvae. • Most vegetative cells of this genus are not pathogenic, and most toxic effects are largely due to the crystals produced during sporulation. P. japonica) larvae

6. Prof. Abdelwahab A. Ibrahim BACTERIA • Bacillus thuringiensis • When B.t. is grown on suitable media it produces heat stable ß-exotoxin in the medium during vegetative growth and before sporulation. This exotoxine affects insects manly during metamorphosis and cause the appearance of malformed insects or prevents pupation. It mainly inhibits polymerization of RNA. • The sensitivity of insects to infection depends on many factors as age, temperature, humidity, food source, etc.. • Insects infected with B.t. stop feeding, became paralyzed in a short time, in addition to a decrease in gut alkalinity and an increase in hemolymph alkalinity which cause septicemia and death. • All members of this group are quite safe to non target organisms especially honeybees. P. japonica) larvae

7. Prof. Abdelwahab A. Ibrahim BACTERIA • Pathogens of Genus Bacillus • B. sphaericus: • Certain strains produce a proteinaceous toxin which poisons mosquito larvae. Host death may also be induced by the spores alone. • B. popilliae: • Produces no toxins in the infection cycle. Japanese beetle (Popillia japonica) larvae ingest spores in the soil which germinate and produce vegetative cells which fill the gut in three to five days. Some cells penetrate the gut wall, then grow and sporulate in the haemolymph. 14-21 days after initial infection the insect body is swollen and creamy white (milky disease). After death, the spores are released into the soil and establish persistent infection sites. • B. cereus: • B. cereus is aSaprophytic non spore forming bacteria. • When insect larvae feed on this bacteria, the body relaxes, and brown spots appear on the skin, then larvae stop motion and the body is covered with brown color. After death the body becomes soft and black , internal body organs crash and sticky exudate appears on the surface. The ability of bacteria to cause disease is largely due to its secretion of phospholipase c enzyme. Similar symptoms were observed When healthy larvae were exposed to the enzyme . It was also found that acidic PH in the gut is necessary for infection. Spore of B popilliae P. japonica) larvae

8. Prof. Abdelwahab A. Ibrahim Thanks