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Disease Cycle and Epidemiology
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Epidemiology
The life cycle of B. longicaudatus has been studied on roots of corn (Zea mays) in axenic root culture. Like other plant-parasitic nematodes, the sting nematode begins life as an egg. Figure 24 shows the process of embryogenesis of B. longicaudatus from the one-celled stage to a first-stage juvenile (J1) that molts inside the egg into a second-stage juvenile (J2) ready to hatch. After hatching, the J2 move through soil to the root system of a host plant where they congregate around root hairs. The J2 feed on the root hairs until they molt into third-stage juveniles (J3). The J3 move immediately to the meristems of either major or lateral roots to feed, as do all subsequent life-stages. The J3 molt to become fourth-stage juveniles (J4), which molt to become adults.
 Figure 24 |
Sting nematodes are amphimictic, meaning that mating is required to produce viable offspring. Therefore, both male and female nematodes are abundant in most populations. Males and females are attracted to each other for reproduction (Figure 25 A, B). Female sting nematodes have a spermatheca, a sperm-storage organ, so only a single mating is required for fertilization of many eggs over time. Eggs are produced separately from each of two paired ovaries, and a single female was observed to lay nine to ten eggs over a 10 to 15 hour period (Figure 26).
 Figure 25 |
 Figure 26 |
Sting nematodes have no long-term survival stage, so populations decline rapidly in the absence of a host. A population decline model for a population of sting nematodes in northern Florida showed a negative exponential decline in numbers during clean fallow, resulting in a 95% decrease after 200 days. Because females can begin laying eggs immediately after feeding, populations can increase rapidly when hosts are planted. However, the virulence of B. longicaudatus may limit population increases. High numbers of sting nematodes at planting can inhibit root development to the extent that food is limited and nematode populations cannot increase beyond a certain level. This is a phenomenon known as a carrying capacity, the maximum number of nematodes that can be sustained on a given host under a given set of conditions. The carrying capacity for a population of B. longicaudatus on cotton in northern Florida was approximately 140 nematodes per 130 cm3 of soil.
Copyright © 2005
by The American Phytopathological Society