Evaluation of Phosphine Resistance in Populations of Sitophilus oryzae, Oryzaephilus surinamensis and Rhyzopertha dominica in the Czech Republic

SIMPLE SUMMARY: Storage arthropods may invade and damage many types of stored commodities, both in developing and developed countries. The continuous worldwide usage of phosphine as a major fumigant for stored grain protection has led to the development of resistance by several major stored-product insect species. There are data on the occurrence of phosphine resistance from different pest species originating from multiple countries and geographical areas, especially in countries that are among the major grain producers in the world. However, the ongoing EU project (novIGRain) has recently enabled a resistance survey of the selected key species of stored-product pests in some EU countries, including the Czech Republic. The presented part of the survey in this publication included more than fifty field populations of the rice weevil, Sitophilus oryzae, the lesser grain borer, Rhyzopertha dominica, and the saw-toothed grain beetle, Oryzaephilus surinamensis, collected in Czech farm grain stores. It was found that the tested Czech populations of O. surinamensis have a relatively lower frequency and level of resistance than the populations of S. oryzae and R. dominica. Based on our results, the occurrence of resistance to phosphine in the Czech Republic is widespread and includes economically important species, which highlights the need for fumigation alternatives as well as the establishment of integrated resistance management programs. ABSTRACT: Phosphine is globally the most widely adopted fumigant for the control of storage pests. Recently, an increase in the frequency of stored-product pest resistance has been observed with significant geographical and interspecific variations. In this context, there are available data for the occurrence of resistant populations from America, Asia, Africa, and Australia, but there are few data in the case of Europe. Therefore, the aim of this work was to evaluate phosphine efficacy in important beetle pests of stored products, i.e., Sitophilus oryzae (L.), Oryzaephilus surinamensis (L.), and Rhyzopertha dominica (F.) sampled from the Czech Republic, using a rapid diagnostic test that is based on the speed to knockdown after exposure. Apart from the standard laboratory populations, which were used as the controls, we tested 56 field populations of these three species, collected in Czech farm grain stores. The survey revealed that 57.1% of the tested field populations were classified as phosphine-susceptible, based on the knockdown method used. However, profound variations among species and populations were recorded. The species with the highest percentage of resistant populations was R. dominica (71.4% of the populations; resistance coefficient 0.5–4.1), followed by S. oryzae (57.1% of the populations; resistance coefficient 0.8–6.9), and O. surinamensis (9.5% of the populations; resistance coefficient 0.5–2.9). Regarding the intra-population variability in response to phosphine (slope of the knockdown time regression), the laboratory and slightly resistant populations of all species were homogenous, whereas the most resistant populations were strongly heterogeneous. Our data show that the occurrence of resistance in the Czech Republic is relatively widespread and covers a wide range of species, necessitating the need for the adoption of an action plan for resistance mitigation.