ecology of phasmids - KLUEDO - Universität Kaiserslautern

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