Delayed mortality, resistance and the sweet spot, as the good, the bad and the ugly in phosphine use

Phosphine is the most commonly used gas for fumigation for durable commodities globally, but there is still inadequate information regarding its efficacy in conjunction with proper concentration monitoring. In a series of bioassays, insect mortality after specific exposure intervals to phosphine in selected species was examined, as well as the appearance of the so called "sweet spot". The species that were tested were: Oryzaephilus surinamensis (L.), Tribolium castaneum (Herbst), Sitophilus oryzae (L.) and Rhyzopertha dominica (F.) with populations that had different levels of phosphine resistance. Evaluation was conducted by using the Phosphine Tolerance Test (PTT), with exposure of the adult stage for 15, 30, 60, 90, 150 and 300 min at 3000 ppm. At the end of these intervals (separate bioassays for each time interval), the insects were transferred to Petri dishes, in which recovery was recorded at different time intervals (2 h, 1, 2 and 7 days). The majority of susceptible populations of all species were instantly immobilized even in the shortest exposure period (15 min), in contrast with resistant populations that were active even after 300 min. After exposure to phosphine, populations and exposure time affected mortality of susceptible populations, whereas resistant populations recovered regardless of species and exposure time. Additional bioassays at the concentrations of 500, 1000, 2000 and 3000 ppm for 1, 3, 5, 20, 30 and 40 h showed the presence of the "sweet spot", i.e., decrease of mortality with the increase of concentration. In fact, for most of the tested species, the "sweet spot" appeared in 1000 and 2000 ppm at a 5-h exposure time, regardless of the level of resistance to phosphine. This observation is particularly important both in terms of the assessment of resistance and in the context of non-linear recovery at elevated concentrations, indicating the occurrence of strong hormetic reversals in phosphine efficacy. © 2021, The Author(s)

Insecticidal effect of Dittrichia viscosa lyophilized epicuticular material against four major stored-product beetle species on wheat

We examined the insecticidal effect of lyophilized epicuticular material of the ruderal species Dittrichia viscosa in four major stored-product beetle species. Furthermore, the potential of this material in progeny production suppression was also evaluated. The water-soluble extract was derived from plants that had been harvested in September 2016, through freeze-drying, in order to create a fine powder formulation. In our bioassays, the powder was applied in four doses on wheat: 0 (control), 1000, 3000 and 5000 ppm and mortality of the exposed individuals was measured after 1, 3, 7, 14 and 21 days of exposure, while progeny production capacity was recorded 65 days later. Among the species tested, Oryzaephilus surinamensis was found to be the most susceptible, followed by Tribolium confusum and Sitophilus oryzae, while Rhyzopertha dominica was not practically affected. Progeny production was particularly reduced for all species relative to the controls. Indicatively, for O. surinamensis, at the highest dose rate, there were only 0.2 adults per vial, while the respective figures for the control exceeded 40 adults per vial. To our knowledge, this study is the first that examined the insecticidal effect of epicuticular material of D. viscosa for the control of stored-grain insect species. Additional experimentation is required to indicate the rationale of using this natural resource-based material under a non-chemical control strategy at the post-harvest stages of agricultural commodities. © 2020 Elsevier Lt

Insecticidal Effect of an Enhanced Attapulgite for the Control of Four Stored-Product Beetle Species

We examined the insecticidal effect of three different dust formulations, which were atta-pulgite (W), attapulgite mix with oregano essential oil with 52% carvacrol (D1), and attapulgite mix with oregano essential oil with 75% carvacrol (D2), in four major stored-product beetle species, Sitophilus oryzae (L.), Tribolium confusum Jacquelin du Val, Rhyzopertha dominica (F.), and Trogoderma granarium Everts. Sitophilus oryzae was the most susceptible at all three formulations, followed by T. confusum and R. dominica. In contrast, T. granarium larvae showed the lowest mortality rates even on the 14th day of observation and at the highest concentration (2000 ppm). Progeny production was particularly reduced for all species relative to the controls. Nevertheless, complete suppression of the offspring was observed only in the case of T. confusum and S. oryzae, while R. dominica was less susceptible to all three dust formulations, giving an average of up to 20 individuals per vial at 2000 ppm. To our knowledge, this study is the first that has examined the insecticidal activity of oregano compounds in combination with attapulgite for the control of stored-grain insect species. Addi-tional experimentation is required to indicate the rationale of using these natural resource-based materials under a non-chemical control strategy at the post-harvest stages of agricultural commodities. © 2022 by the authors. Licensee MDPI, Basel, Switzerland

Assessment of different inert dust formulations for the control of Sitophilus oryzae, Tribolium confusum and Aphis fabae

The necessity to ensure the quality of food by simultaneously reducing the environmental footprint due to the extensive use of convectional insecticides has led to an increase in the efforts towards the development of non-chemical control strategies. Silicon dioxide is considered as a promising alternative active ingredient for the control of various arthropods in different crops and products. Silicon dioxide and the relative silicaceous materials (silica) are classified in the category of inert dusts, which act on arthropods through contact leading to desiccation. In our study, we tested three different silica-based dust formulations, Sylobloc® S200, Syloid® ED3 and Syloid® ED5 in order to evaluate their pest control efficacy. As target species, we used, in laboratory bioassays, a field/greenhouse pest the aphid Aphis fabae and the stored-product pests Tribolium confusum and Sitophilus oryzae. These species were exposed to the aforementioned dusts under three different doses (0, 12.5, 25.0 mg/petri) and different time intervals. Taking into account the exposure time of the above species to the inert dusts, S. oryzae adults and T. confusum larvae were more susceptible to ED5 at 25.0 and 12.5 mg, respectively, while A. fabae adults to S200 at the highest tested dose, since less time was needed in order to achieve the highest mortality. Sitophilus oryzae and T. confusum mortality was increased to 90% after the 7th day of post exposure period to all dust formulations, while the highest mortality levels of A. fabae were recorded after 1 day of post exposure to S200. The results of this study show that these silicon dust formulations are effective to greenhouse and storage insect control and can be further exploited through various uses, e.g. in insect-proof nets to minimize the pest invasions in greenhouses. © 2020 Elsevier Lt

Population Growth Changes in Major Stored Product Insects on Rice Fortified with Spearmint and Basil

Rice is the most important durable food product for more than half of the world’s population, as it is very nutritious food in terms of carbohydrate containment and can meet a large part of human caloric needs on a daily basis. The sensitivity of a rice product fortified with spearmint or basil was evaluated for three stored product insect species: Sitophilus oryzae (L.) (Coleoptera: Curculionidae), Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae) and Oryzaephilus surinamensis (L.) (Coleoptera: Silvanidae). Five different containments of fortified rice were used (0, 25, 50, 75 and 100% of the total rice quantity), and the population growth of the above species was examined after 65 days. We found that fortification generally reduced the infestation level of the species tested and reduced their population growth, as compared with the control rice. In some of the treatments, there were some differences between the application of spearmint and basil. There was higher frass production in the rice that had been fortified with basil than that with spearmint, indicating different infestation patterns. For S. oryzae, with the gradual increase in fortification, the number of insect-damaged kernels and weight of damaged kernels reduced, and significant differences were recorded between the fortification with spearmint and that with basil. The results of the present study are certainly encouraging for further utilization of the characteristics of fortified rice for stored product insect control. © 2022 by the authors

Evaluation of silica-coated insect proof nets for the control of Aphis fabae, Sitophilus oryzae, and Tribolium confusum

Insect proof nets are widely used in agriculture as mechanical and physical barriers to regulate pest populations in a greenhouse. However, their integration in the greenhouse ventilation openings is highly associated with the decrease of air flow and the adequate ventilation. Thus, there is need for alternative pest management tools that do not impair adequate ventilation. In the present study, we tested four net formulations of relatively large mesh size coated with SiO2 nanoparticles, namely, ED3, ED3-P, ED5, and ED5-P to evaluate their insecticidal properties against adults of Aphis fabae and Sitophilus oryzae and larvae of Tribolium confusum. ED3 and ED5 nets were coated with SiO2 nanoparticles of different diameter, while in the case of ED3-P and ED5-P, paraffin was added to increase the mass of the deposited particles on the net’s surface. In the first series of bioassays, the knockdown and mortality rates of these species were evaluated after exposure to the aforementioned net formulations for 5, 10, 15, 20, 25, 30, 60, 90, and 180 min. In the second series of bioassays, knockdown and mortality of these species were recorded after 1, 7, and 10 days of post-exposure to the nets for different time intervals (15, 30, and 60 min). Based on our results, all nets significantly affected A. fabae, since all insects were dead at the 1-day post-exposure period to the silica-treated nets. Conversely, at the same interval, no effect on either S. oryzae adults or T. confusum larvae was observed. However, in the case of S. oryzae, the efficacy of all nets reached 100% 7 days after the exposure, even for adults that had been initially exposed for 15 min to the treated nets. Among the species tested, T. confusum larvae exhibited the lowest mortality rate, which did not exceed 34% at the 10 days of post-exposure interval. Our work underlines the efficacy of treated nets in pest management programs, under different application scenarios, at the pre-and post-harvest stages of agricultural commodities. © 2020 by the authors. Licensee MDPI, Basel, Switzerland