Entomopathogen based autodissemination for the control of plodia interpunctella (Hübner): an examination of the critical components

Abstract

Plodia interpunctella (Hübner) is a major pest of raw and processed stored food products and the purpose of this work was to design and determine whether an entomopathogen based autodissemination approach would be an efficacious product for its control. A comparison of the retention, horizontal transmission and effect on mating of two electrostatic entomopathogen delivery powders (Entomag™ and Entostat™) was made to evaluate their potential as a component of an autodissemination method for the control of P. interpunctella. Both powders were shown to have some effects on mating behaviour and ability of treated males to locate a pheromone source when applied in high doses. However, no effects were observed at rates consistent with the amount of powder that was actually taken up when the moths visited a prototype bait station device. Male and females lost 69.9 and 64.3% by weight respectively of Entomag by 48h after exposure but lost more Entostat, 89.8% and 75.9%, over the same period. Critical to the efficacy of autodissemination is the transfer of powder from males to females and on average a 49% greater weight of Entostat was transferred than Entomag. In addition to this the electrostatic charge on each powder was measured, with Entostat charging significantly more (to the negative polarity) than Entomag. The respective distances that a charged particle could levitate by virtue of electrostatic forces to an insect, were modelled, with Entostat predicted as levitating over a greater distance to the moth than Entomag under scenarios where the insect was either neutral or charged (neutral particle = 2.8 mm, compared to 1.9 mm; charged particle = 21.7 mm, compared to 6.8 mm). A novel technique for determining powder uptake by P. interpuncetlla was developed based on image analysis. This determined the regions of the moth’s body to which particles were more likely to adhere. This study confirmed that pit-fall style powder dispensers were more effective at delivering powder to the head of the moth, where powder appeared to be most readily horizontally transferred between conspecifics. Finally, an individual based modelling approach was taken to determine the overall suitability of Beauveria bassiana autodissemination as a controlling strategy for P. interpunctella. The model suggested that a maximum of only 62% of male moths would become contaminated with entomopathogen and that this would be insufficient to cause a decline in the overall population.

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