Quantifying time-mortality relationships for nuclear polyhedrosis viruses when survivors are present
1998
Farrar, R.R. Jr | Ridgway, R.L.
The time-mortality relationship for nuclear polyhedrosis viruses (NPVs) is 1 of the more important factors to be considered in the development of NPVs as biological control agents. This factor has become of particular interest in recent years with the advent of NPVs that have been genetically modified to kill insects faster. However, much information published on time-mortality relationships is quantified in such a way that the results may be misleading. In quantifying time-mortality relationships for NPVs, many researchers calculate median lethal times (LT50S), or median survival times (ST50S), using probit or similar analyses. However, some researchers include insects that survive the treatment in their calculations, whereas other researchers do not include survivors. Simulated data are presented to show that when survivors are included, treatment effects on LT50S and ST50S are inherently influenced by any treatment effects on percent mortality. Examples of real data from bioassays of the NPV of the celery looper, Anagrapha falcifera (Kirby), against the corn earworm, Helicoverpa zea (Boddie), and the beet armyworm, Spodoptera exigua (Hubner), that illustrate the same pattern are also presented. Rationale is presented that if survivors are simply not infected, data on them represents no useful information on the time-mortality relationship, and so survivors should generally be excluded from calculation of LT50S or ST50S, as well as from alternative methods of quantifying this relationship. Data on percent mortality data should be presented as well to allow full evaluation of the experiments.
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