1) An investigation was undertaken into the various activity rhythms found in the larvae of Myrmeleon obscurus (Neuroptera, Myrmeleontidae). Pit construction was used as the criterion of activity. 2) The capacity sensitive electronic circuit used to monitor the daily pit building activity is described. 3) Various factors affecting the size of the pits constructed by ant-lion larvae were investigated. Pit size was found to be correlated with the size of the larvae, larger larvae constructing bigger pits. Population size was also shown to have an effect, since the more crowded the animals were the smaller and closer together their pits became. The death rate due to competition between the larvae also increased as the ant-lions became more crowded. 4) Feeding frequency also affected pit size. Ant-lions which were starved constructed very small pits. 5) Pit size was affected by the texture of the sand, maximal pit size being attained in sand with a grain size of between 353 μ and 211 μ. This was shown to be the most abundant grain size in sand from the natural habitat. In sand coarser or finer than this, pit size was reduced. 6) Generally smaller pits were constructed at lower temperatures, but this response depended largely on the lunar cycle. The upper and lower critical limits for pit construction were found to be 11° C and 42° C. Below and above these temperatures no pits were constructed, although the ant-lions remained alive. 7) Daily destruction of the pits decreased the pit size. 8) The existence of the daily pit building activity rhythm, which occurs at dusk, was demonstrated in individuals and in populations of ant-lion larvae. This rhythm was studied using the capacity sensitive circuit, and also by direct observation of groups of animals over a 24 hour period. 9) The daily activity rhythm appeared to be endogenous, since it continued for at least a month both in constant light and in constant dark. The rhythm was altered by reversals in the daily light-dark cycle, and it was concluded that light was the main phase setting factor. 10) An attempt was made to determine the location of the "clock" or "clocks" controlling the daily activity rhythm. This was investigated by chilling the heads of individual ant-lions with a fine copper wire, and also by chilling large groups of animals in the refrigerator. From these experiments no definite conclusions could be drawn about the location of the "clock". 11) The existence of a lunar pit building cycle was demonstrated in both field and laboratory populations of ant-lions. Maximal pit size was attained at full moon. Very low temperatures were found to suppress these lunar peaks. 12) The lunar pit building rhythm was shown to be endogenous, since it continued for at least two months in constant dark and one month in constant light. 13) The lunar pit building rhythm of very young larvae was investigated, and it was shown that while larvae which hatched in the field appeared to possess a lunar rhythm, larvae which were hatched in the laboratory did not have a rhythm. It was therefore concluded that the light of the moon was necessary to establish the lunar rhythm. 14) Some possible explanations for the lunar cycle were investigated experimentally. It was concluded that the lunar rhythm was not related to the number of prey present at various times of the lunar cycle or to the spacing of the animals in their habitat. The lunar rhythm was shown to be due to the combination of a lunar day activity rhythm and a solar day activity rhythm. 15) Some aspects of the daily rhythm are discussed, and this rhythm is compared with those found in other insects. Probable functional reasons for the rhythm are presented. Summary, p. 133-136.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:rhodes/vital:5868 |
| Date | January 1968 |
| Creators | Morrison, G J |
| Publisher | Rhodes University, Faculty of Science, Zoology and Entomology |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis, Masters, MSc |
| Format | 150 leaves, pdf |
| Rights | Morrison, G J |
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