ecology of phasmids - KLUEDO - Universität Kaiserslautern
ecology of phasmids - KLUEDO - Universität Kaiserslautern
ecology of phasmids - KLUEDO - Universität Kaiserslautern
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Life history & potential population growth 34<br />
P. hispidum, P. reticulatum, etc.). At the end <strong>of</strong> an observation I carefully searched the container and the<br />
remainders <strong>of</strong> the leaves for eggs. In total, I yielded 500 observational days from 99 individual females.<br />
Multiple observation units per female individual were averaged.<br />
Because individual fecundity <strong>of</strong> females may be influenced by female body size (weight) (e.g., Price<br />
1984) female weight was correlated to egg production in a Spearman Rank correlation. For this analysis<br />
I only included females that had laid at least one egg while being under observation (49 females). The<br />
elimination <strong>of</strong> zero counts for female oviposition (50 females) was justified by the fact that the<br />
disposition to lay eggs was independent from female weight (comparison <strong>of</strong> weight for females having<br />
laid eggs and females not having laid eggs: T = -0.54; df = 97; P = 0.59).<br />
For the estimation <strong>of</strong> the proportion <strong>of</strong> females in M. diocles populations, I calculated sex ratio for the<br />
lab population on the base <strong>of</strong> the numbers <strong>of</strong> emerged adult males and females.<br />
The mean generation time <strong>of</strong> M. diocles was measured on the basis <strong>of</strong> the mean duration its three<br />
distinct life stages: (1) developmental time <strong>of</strong> eggs, (2) developmental time <strong>of</strong> nymphs (maturation) and<br />
(3) adult lifetime.<br />
Mean developmental time <strong>of</strong> eggs was derived from observations <strong>of</strong> the hatching <strong>of</strong> nymphs from eggs<br />
with known date <strong>of</strong> oviposition. Eggs were collected from cages at least every third day and stored in<br />
plastic food containers covered with mesh. Containers were labeled with the date <strong>of</strong> oviposition and<br />
stored in plastic boxes with 10 mm <strong>of</strong> sand on the bottom. Eggs were sprayed with water regularly to<br />
provide for ambient humidity. Hatching <strong>of</strong> nymphs was controlled daily.<br />
If eggs fail to hatch, for example due to fungal infestation (Bedford 1978), then this reduced hatching<br />
success will negatively affect population growth. To describe the influence <strong>of</strong> failed hatching on<br />
population growth, I assessed hatching success. Infestation <strong>of</strong> eggs by fungi (notable by fungal hyphens<br />
covering the eggshell) was checked once per month. Infested eggs were collected and kept separately to<br />
observe hatching (no hatching <strong>of</strong> infested eggs occurred). In January 2002 I counted all eggs that were<br />
older than 120 days and had not hatched. I assumed that these eggs had failed to hatch because less than<br />
0.31 % <strong>of</strong> almost 2000 eggs took longer than 120 days for development. I randomly selected 10 <strong>of</strong> these<br />
eggs and opened them: one contained a dead dry nymph, four were dried out, and in five the usually<br />
green liquid had turned black.<br />
Mean developmental time <strong>of</strong> nymphs was assessed from individually raised nymphs. A nymph was set<br />
in a plastic container with screened lids. At least every third day individuals were provided with fresh<br />
leaves <strong>of</strong> Piperaceae or Araceae (see Chapter 2) and the containers were cleaned. Nymph development<br />
was controlled daily.<br />
Average adult lifetime was calculated on the base <strong>of</strong> individuals with certified records <strong>of</strong> date <strong>of</strong><br />
emergence and death from July 2000 to January 2002. The lab population <strong>of</strong> M. diocles was checked at<br />
least weekly for new emerged and dead adults. New adults were measured from head to terminal