The Dispersal of the Variegated Grasshopper, Zonocerus Variegatus (Linnaeus) (Orthoptera, Acridoidea, Pyrgomorphidae), in Open Fields and Cultivated Farms
Marked individuals of Zonocerus variegatus were released in batches of 100 per developmental cohort at definitive loci in either an open field of mainly giant star grass, Cynodon sp. or a cultivated farm of cassava, Manihot esculenta. The distance and direction of movement of individuals in any given stadium were determined in metres and angular degrees. The mean distances moved by marked Z. variegatus for each day of observation were determined by Clark’s root mean square formula.
The results showed that older cohorts covered more distance during a given period than young cohorts. However, while the first instar nymphs moved significantly less than any other cohort, the differences in the mean daily distances moved by nymphs of the second through the sixth developmental instars in the cassava farm were not statistically significant. For all cohorts, Z. variegatus covered significantly more distances in the open field than in the cultivated farm, suggesting that the availability of food inhibited the rate of dispersal of Z. variegatus. There was no significant difference in the number of Z. variegatus found on the different aspects of the compass.
Key WordsDispersal variegated grasshopper Zonocerus variegatus cultivated farm open field cassava control
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