|
April 2005. A question from Taiwan: how can one determine the life table of Ganaspidium utilis (Beardsley) (Hymenoptera: Eucoilidae), a solitary, larvae-pupal parasitoid of Liriomyza trifolii and L sativa? How can the mortality of egg, larvae, prepupa and pupal stages be determined: without dissection, the developmental stages cannot be determined, but if dissected, the mortality cannot be estimated.
The following answer was provided by a member:
Destrucive sampling at intervals would seem to be one possibliity. Take a population of 1000 host individuals exposed to the parasatoid. Sample five percent of that initial population and look of infestation (egg-laying). This gives you a percent “infection” rate (or could one introduce the eggs artifically to create 100% infection?). Then sample 5% of the remaining population at weekly intervals (could be more or less frequently depending on the development rate of the parasatoid) and record the number infested with eggs and the number infested with different larval satges. Any decline in the presence of eggs from the initial sampling is egg mortality unless it can be accounted for development of a larva. It works similarly for development of larval instars or other stages.
This data could then be nicely modelled in a Lefkovitch population matrix containing the probabilities of remaining in the same stage (larval instar, egg, etc.) and the probabilities of moving to another stage. One minus the sum of these probabilities is the mortality. There are programs (RAMAS stage is one) that will let you sample from a probability distribution with a known form, mean, and standard deviation in parameterizing your matirx.
Another member said:
It is possible to construct a life table and survivorship curves for endoparasitoids. Since the eggs, larvae and pupae are found within the host, microscopic dissection of the host is a must. Try to find out the number of eggs laid per female per clutch and then follow up the cohort till adult emergence or death. A survivorship curve of Brachymeria sp. has been developed this way. Parasitised host pupae were collected from the field, kept in the lab till the adult parasitoids emerged, then the hosts were dissected under a microscope and the dead larvar counted.
|
