Synthetic amorphous silica for post-harvest control of Tribolium castaneum and Plodia interpunctella in California tree nut commodities

The Californian almond and pistachio industry is valued at an estimated value of $8.1 billion. After harvest, almonds and pistachios are stored for several weeks outdoors under tarps, or in shipping containers in open facilities, where they are susceptible to a variety of post-harvest insect pests. Phosphine fumigation is the industry standard for management of post-harvest pests of tree nuts. However, increasing rates of phosphine resistance in storage pests has called phosphine’s sustainability into question. Here we present research investigating the use of Synthetic Amorphous Silica (SAS), and industrial silicon-dioxide product, to manage lepidopteran and coleopteran post-harvest pests of almonds and pistachios under diverse temperature and humidity treatments. Growth chamber experiments were performed to assess the efficacy of SAS against two common post-harvest pests of tree nuts, the coleopteran Tribolium castaneum (Herbst) and the lepidopteran Plodia interpunctella (Hubner). Surface treatments of unmodified SAS were found to significantly reduce populations of both pests by >85% relative to control. This effect was found in both almonds and pistachios. SAS proved effective at doses as low as 200g/ton, less than is required from conventional silica-based insecticides such as diatomaceous earth. Initial findings suggest that SAS’s efficacy is robust under diverse temperature (66°F, 77°F, 92°F) and relative humidity treatments (30%, 55%, 75%). This suggests that SAS may serve as an efficient addition to the IPM toolbox for post-harvest pests. However, refinement of application techniques and investment in field treatments of harvested nuts may further increase the product’s efficacy.