Using viable eggs to accurately determine the demographic and predation potential ofHarmonia dimidiata(Coleoptera:Coccinellidae)

Abstract

Life table parameters and predation rate of the coccinellid predator Harmonia dimidiata F. fed on Aphis gossypii Glover were determined at 25°C using the age‐stage, two‐sex life table. When the total number of eggs were included in our calculations, the intrinsic rate of increase (r), finite rate (λ), net reproductive rate (R0) and mean generation time (T) for H. dimidiata were 0.1354/day, 1.1450/day, 280.8 offspring and 41.6 day, respectively. These values were significantly different, however, only when viable (=hatchable) H. dimidiata eggs were counted (0.0909/day, 1.0952/day, 67.6 offspring and 46.3 day, respectively). The values obtained using all eggs did not realistically reflect the effect of variable hatch rate and true population parameters of H. dimidiata. We therefore excluded unhatched eggs from our data and demonstrated mathematically that in future demographic studies, it should be a standard procedure to exclude all unhatched eggs when analysing hatch rates that vary with maternal age. A mathematical proof was derived in this study to substantiate this. To observe and quantify variations that occur in the predation rate due to the age and stage of the predator, the daily number of A. gossypii consumed by individual H. dimidiata was analysed using the age‐stage, two‐sex life table. The net predation rate of H. dimidiata on A. gossypii was 14 804 aphids. The transformation rate Qp showed that the predator needs to consume an average of 219.1 aphids to produce one viable egg. The finite predation rate of H. dimidiata was 125.7 when only hatchable eggs were included in the analysis. Because the age‐stage, two‐sex life table takes both of the sexes and the variable predation rate occurring among stages into consideration, it becomes possible to use the population projection to quantify and time biological control procedures.

Invariance of demographic parameters using total or viable eggs

“…Results and Discussion Mou et al (2015) fail to consider that egg viabilities h x are closely related to N e /N, that is:…”

“…It should be considered that initial eggs of parent population are a random sample and thus they were produced by females from different ages; thus, the egg viability of the parent population should not be different from that observed during the experiment. The high egg viability observed in the parent cohort compared with the low viability observed in the first generation would suggest that these eggs came from females of intermediate ages, where Mou et al (2015) observed the highest peak of hatch rate.…”

“…Most of the key methodological and procedural publications have been summarized in many books: since the seminal book by Dublin et al (1949), to the classical textbook of Southwood (1978) and the most recent one of Carey et al (1993). Chi and Liu (1985) proposed a theory of both agespecific and stage-specific life table and a combined age-stage, two-sex life table method; later their proposed methodology was reviewed in a recent article in this journal (Mou et al 2015), recommending that in insect population studies in which hatch rate varies with maternal age, demographic parameters should be calculated excluding unviable eggs. In this note, we expose a flaw in their arguments and show that estimates of demographic parameters (R 0 , T, r and k) do not vary by considering either all eggs or only viable ones.…”

“…which is the average number of viable eggs produced by a viable egg. Mou et al (2015) in equation 25 claim that if the hatch rate of eggs laid by the females in the cohort at different ages is not the same as that of the parent cohort, that is if:…”

Host plants mixture and fitness ofKolla paulula: with an evaluation of the application of Weibull function

“…The relative humidity inside the plastic cylinders was monitored by a HOBO data logger equipped with a small diameter external sensor (Onset Computer Corporation, Bourne, MA, US). Because we had previously observed that K. paulula preferred to oviposit on pilose beggarticks and that the hatch rate varied with female age, newly hatched nymphs from a cohort of 114 eggs laid on pilose beggarticks within a 24-hr period were used to begin the life table study (Mou et al 2015). Newly hatched nymphs were transferred to individual plastic cylindrical rearing cages (20 cm in height, 7 cm in diameter and covered with 100 mesh nylon screen) and placed on a plastic pot (7.6 cm in diameter) containing one plant each of pilose beggarticks and trilobate wedelia.…”