Oligonychus afrasiaticus

Chaaban, Sameh Ben, Chermiti, Brahim & Kreiter, Serge, 2012, Effects Of Host Plants On Distribution, Abundance, Developmental Time And Life Table Parameters Of Oligonychus Afrasiaticus (Mcgregor) (Acari: Tetranychidae), Papéis Avulsos de Zoologia 52 (10), pp. 121-132 : 121-132

Estimation of O. afrasiaticus reproductive

parameters and longevity

Pre-oviposition, oviposition and post-oviposition periods, total fecundity, daily oviposition rate and female longevity were determined on each of the six host plants. For each host plant, 50 deutonymphal (2 nd nymph stage) females were randomly selected from the corresponding colony. To ensure mating, two adult males were placed with each newly emerged adult female. Females were confined individually per leaf disk or date fruit and observed daily. The number of eggs deposited by each female was recorded daily until all the females died. The eggs obtained from each female were cultured to determine their hatchability. Pre-oviposition period was recorded at 6-h intervals, while other reproductive parameters and longevity were recorded every 12 h. Dates and leaf disks were removed and replaced by new ones at 2-day intervals.

Sex ratio

Sex ratio is described as the proportion of females in the progeny. We evaluated sex ratio of twenty O. afrasiaticus females, for each host plant. The meth- od was the same as that used for oviposition, except that females were placed on a new leaf disc every day and discs with eggs were maintained under the same experimental conditions as for females. The sex ratio was determined on the basis of a count of adults originating from those eggs. Unmated females, i.e. producing only males, were not taken into account.

Life tables

The life table was constructed considering the females cohort studied. The net reproductive rate (Ro), the mean generation time ( T), the intrinsic rate of natural increase (rm), the doubling time (Dt), and the finite rate of increase (λ) were calculated using the method recommended by Birch (1948):

K

1 = ∑ e −r m x (l x m x) X =0

With x pivotal age, lx number surviving to age x,

mx age-specific fecundity

• Ro = Σ lx.mx

• rm = ln(Ro)/ T

• Dt = ln 2/ rm

• T = ln Ro/ rm

• λ = e - rm

Statistical analysis

Data on developmental time, duration of female reproductive periods and fecundity were analyzed using one-way ANOVA followed by the Sheffe test (P = 0.01) to compare data means. Differences in sex ratio were analyzed by a Khi square (λ 2) test. The statistical analysis was done by the statistical software SPSS 10 (Statistical Package for the Social Sciences version 10).