HISTOPATHOLOGICAL AND HISTOCHEMICAL CHANGES IN HONEYBEE LARVAE (APIS MELLIFERA L.) AFTER INFECTION WITH BACILLUS LARVAE,THE CAUSATIVE AGENT OF AMERICAN FOULBROOD DISEASE

Morphological, histochemical and cytochemical changes were examined in honeybee larvae after infection with the bacterium Bacillus larvae. The results indicate cell necrosis in the midgut epithelium accompanied by increasing cell vacuolization and nuclear pyknosis following per os inoculation with B. larvae. Many autolysosomes were positive for acid phosphatase. Non-vacuolar acid phosphatase activity was also found in lysed cell compartments. No such activity was found in regenerative epithelial cells. Degradation of haemocytes, salivary glands and other tissues was also observed. Histochemical analyses after per cutaneous inoculation with B. larvae of three- and five-day-old honeybee larvae show intense non-vacuolar acid phosphatase activity followed by disintegration of infected salivary glands, epithelial cell cytoplasm and haemocytes.     

Submerged macrophytes, zooplankton and the predominance of low- over high-chlorophyll states in western boreal, shallow-water wetlands

1. Shallow‐water (<2 m deep) wetlands in northern Alberta's western boreal forest tend to have either extremely high‐chlorophyll, pea‐green water or water that is low in chlorophyll and clear. The relative importance of top‐down processes (e.g. zooplankton grazing) compared with bottom‐up processes (e.g. nutrient limitation) for regulating the existence of these alternate states has yet to be explicitly investigated in these poorly studied waterbodies. 2. To assess the relationship between chemical and biological factors and the predominance of low‐chlorophyll over high‐chlorophyll states, a survey of 24 shallow‐water wetlands in northern Alberta was conducted over the summers of 2001 and 2002. 3. In wetlands without fish, statistical analysis indicated that high‐ and low‐chlorophyll sites could be differentiated with 82% accuracy based solely on whether submerged aquatic vegetation (SAV) coverage was greater or less than 25%. Further, high‐SAV lakes with zooplankton communities dominated by large cladocerans were clear 96% of the time. 4. In the few wetlands that supported stickleback populations, large cladocerans were absent. However, the development of zooplankton communities dominated by small cladocera (Bosmina) with calanoid copepods in fish‐containing wetlands corresponded with a shift from high‐ to low‐chlorophyll states. 5. Results suggest that in fishless wetlands high‐SAV coverage and grazing by large, SAV‐associated cladocerans promotes low‐chlorophyll states. Results also suggest that suppression of macroinvertebrate predators by sticklebacks allowing Bosmina to flourish may also promote low‐chlorophyll, clear‐water conditions.     

THE SPREAD OF DISEASES CAUSED BY SPECIES OF VERTICILLIUM

An investigation has been made of the spread of Verticillium disease of tomato and antirrhinum by root contact between diseased and healthy plants, and by the growth of the fungi through the soil. V. alboatrum and V. Dahliae spread rapidly by root contact, while V. tricorpus, V. nigrescens and V. nubilum showed no appreciable spread. Where the tomato and antirrhinum hosts wilted and died the causal organism was invariably isolated from the soil near the roots of the dead plants, but where the inoculated host harboured species without showing disease symptoms, as in the case of V. tricorpus and V. nubilum in antirrhinum, the parasite was never obtained from the soil. Moreover, these species in antirrhinum, and V. nigrescens and V. nubilum in tomato would appear to be mild pathogens since when they were already well established V. alboatrum was later actually found to enter and parasitize the respective hosts and bring about its own typical disease symptoms.
Spread through the soil in the absence of hosts was tested by the insertion into it of infected wheat grains followed by later attempts to isolate the fungi at varying distances from the point of infection. V. alboatrum, V. Dahliae and V. tricorpus showed little or no growth through the soil, whereas V. nigrescens and V. nubilum spread saprophytically to some extent, though never attaining sufficient concentration to cause appreciable infection of later planted tomatoes.
The conclusion is reached that spread of disease caused by species of Verticillium takes place mainly by root contact, with a rapidity relatively proportional to that of the death of the host. This finding, together with the lack of spread from antirrhinum plants infected with the non-lethal V. tricorpus and V. nubilum , suggests that the parasites remain in the vascular tracts until the death of the hosts.     

WILT OF LUCERNE CAUSED BY SPECIES OF VERTICILLIUM

The incidence and symptoms of a disease of lucerne induced by Verticillium spp. are much less severe immediately after the crop has been first cut than later when the crop has matured. Infection becomes more marked as the season advances and the age of the ley increases, and cuts taken in the third harvest year are proving unprofitable.
In cross-inoculation studies the causal organisms of lucerne wilt, V. albo-atrum and V. dahliae prove to be only mild pathogens to hop, potato, tomato and antirrhinum, and are not pathogenic to sainfoin and clover. The last two may therefore be cultivated as fodder crops in those areas most severely affected by lucerne wilt, but the cultivation of potatoes after lucerne should be discouraged, particularly if lucerne is to be sown in future years, since the potatoes might build up a reservoir of inoculum of the lucerne pathogen. In studies of host-parasite relations it is shown that V. albo-atrum and V. dahliae from lucerne, V. albo-atrum from hop, V. tricorpus from tomato and V. nigrescens and V. nubilum from potato vary in their effects upon lucerne seedlings growing on agar media, V. albo-atrum from lucerne being, as in the field, the most virulent and the only one to reach the xylem vessels under the conditions of the experiments.
The dressings Agrosan-GN (containing mercury) and Fernasan (containing thiram) are toxic both to spores of Verticillium on lucerne seed coats and to infected plant material carried with seed, and although they are also toxic in vitro to Rhizobium mellelotus this did not prevent dressed seeds which had been inoculated with the bacterium from developing into healthy seedlings bearing normal root-nodules.     

Nutritional Requirements of Blastocrithidia culicis,a Trypanosomatid with an Endosymbiont1

ABSTRACT. The symbiont-containing Blastocrithidia culicis from Aedes vexans, unlike most lower trypanosomatids cultivated in defined media, require only three amino acids: methionine, histidine, and arginine; only three vitamins: thiamin, nicotinamide, and riboflavin; and neither heme nor purine. The bacterium-like endosymbiont presumably provides the trypanosomatid's other essential nutrients.