The influence of greenhouse chrysanthemum on the interaction between the beet armyworm,Spodoptera exigua, and the baculovirus SeMNPV: parameter quantification for a process‐based simulation model

During the building of a process‐based simulation model for the epidemiology of the multicapsid nucleopolyhedrovirus ofS. exigua(SeMNPV) in populations ofSpodoptera exigua(Hübner) in greenhouse chrysanthemum, it was found that the effect of host plants had been under‐rated. ‘Missing links’ included (i) the ‘natural’ background mortality of larvae ofS. exiguain practical cropping conditions; (ii) the developmental rate of larvae ofS. exiguaon plant substrate in a glasshouse as compared to artificial medium in the laboratory; (iii) the validity of the results of dose‐mortality and time‐mortality bioassays conducted on artificial medium as compared to natural plant substrate; (iv) the distribution of inoculum released from deceased caterpillars over chrysanthemum leaves; and (v) the leaf visit rate of healthy caterpillars (as it affects horizontal transmission). Experiments were carried out to quantify these processes. Developmental rates ofS. exigualarvae on greenhouse chrysanthemum were 36% lower than on an artificial diet. The fraction survival during the first, second, third and fourth instarS. exigualarvae in greenhouse chrysanthemum was 0.60, 0.80, 0.88 and 0.95, respectively. Forty percent of the first instar larvae reached the fifth larval stage. Second instarS. exigualarvae reared on chrysanthemum were significantly more susceptible to SeMNPV than larvae reared on an artificial diet. The food source had no effect on the time to killS. exigualarvae. Cadavers of second, third and fourth instarS. exigualarvae contaminated on average 1.4, 2.5 and 3.3 chrysanthemum leaves. Second to fourth instarS. exigualarvae visited 2–3 leaves per day and spent 15–55% of the time on the underside of leaves. The above information is of critical importance for a trustworthy simulation of the epidemiology of SeMNPV in chrysanthemum.