Abstract
The most dominant pest of date stored in Khuzestan Province is Ephestia kuehniella Zeller (Lepidoptera: Pyralidae). In this study, the effects of Bacillus thuringiensis Kurstaki bacteria and Beauveria bassiana pathogenic fungi on the population dynamics of E. kuehniella date stock pest were investigated. To fulfill this, insectariums were kept in vitro at an average temperature of 27 ± 5 °C and a RH of 40 ± 5% for a duration of 6 months, equivalent to the maximum permitted shelf life of date. For sampling from 3 heights in 3 rows, one hole was randomly selected and a sample equal to 20 g of date was taken. Three samples were taken from each insectarium. During 25-week storage period of date treated with B. bassiana and Btk, 6 outbreaks occurred in the population of E. kuehniella. The mechanism of the epidemic is in the way that, once the population has increased to a certain threshold, the incidence of the pathogenic epidemic will be mass-dependent, leading to a decreasing trend in the pest population. Therefore, population reduction was estimated to be at 6 to 32 times that of the control. The highest disease mortality rate occurred at the egg and larval developmental stages, so the pathogens caused the highest mortality before the population entered the reproductive stage. Gradually, from the egg growth stage to the complete insect stage, a reduction was observed in the number of individuals which entered the subsequent growth stage. At all stages, the reduction in the treatment population group was faster than the control population. The highest reduction in the number of individuals entering the next developmental stage was associated with the larval developmental stage, followed by developmental stages of the adult, pupal, and egg. Regarding the highest potential of B. bassiana and BtK in reducing the stock pest population, it is very possible to exploit this interaction for biocontrol.Graphical abstract
Highlights
The production of date in Iran is more than one million two hundred thousand kilograms per year
Where Eq (1), Fij is the number of individuals at the age of Ith afterwards at time j. hi and hi+1 are the sampling intervals between the time i and the time (Wootton and Bell 1992 and Wisdom and Mills 1997). q is the number of growth stages, fj(t) is number of population at stage j for part of the population sampled at time t
Fj(t) is the number at growth stages j, j + 1, q... for part of the population sampled at time t
Summary
The production of date in Iran is more than one million two hundred thousand kilograms per year. Recent trends in support of biological pesticides include the use of microbial agent mixtures (Sharifzadeh et al 2018) This approach can lead to the prevention or delay in the development of insect resistance (Sudo et al 2017), especially when the individual components of the preparation have different modes of action (Zhu et al 2016). This strategy reduces costs (Das 2014) and preparation concentrations because microbial agent increases each other’s activity and act synergistically (Wright and Ramos 2005). The population density of the pathogen is a mass-dependent factor (Gaugler and Kaya 1990)
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