Modelling heat-disinfestation of dried fruits on “biological model” larvae Ephestia kuehniella (Zeller)

Individual and combined effects of contact insecticides and high temperatures on Mediterranean flour moth, Ephestia kuehniella Zeller (Lepidoptera: Pyralidae)

BACKGROUND

Mediterranean flour moth or mill moth Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) is a common pest of cereals and flour throughout the world. In this study, eggs, third instar larvae, pupae and adults of E. kuehniella were exposed to five elevated temperatures at a range of 45 to 65 °C for 5, 8, 10, 14, 18, 23 and 30 min. The effect of cypermethrin and dichlorvos was assessed on third instar larvae. The larvae were exposed to the insecticides on glass and concrete arenas and their mortality was recorded 24 h after treatment. To determine combination effects, the third instar larvae were transferred into the Petri dishes treated with LC₂₅ (lethal concentration that kills 25%) of each insecticide and exposed to high temperatures for the period of time equal to LTi₂₅ values (time needed for killing 25% of tested insects).

RESULTS

Exposing the eggs, third instar larvae and adults of E. kuehniella to 55 °C for 30, 18 and 30 min respectively, resulted in 100% mortality. In the pupa, exposure to 65 °C caused 100% mortality after 23 min. Based on the LTe₅₀ values (temperature needed to cause 50% mortality in the tested population), pupa was the most tolerant life stage to the temperatures tested. The LC₅₀ values of cypermethrin and dichlorvos were 423.1 and 2608.5 mg active ingredient (a.i.) L^-l on glass, and 2525.0 and 13502.8 mg a.i. L^-l on concrete, respectively. The effect of cypermethrin was synergized by high temperatures.

CONCLUSION

High temperatures, cypermethrin and dichlorvos were effective against E. kuehniella. Exposure to combination of lower doses of cypermethrin and high temperatures at short time intervals may have potential in managing this pest. © 2021 Society of Chemical Industry.

Overproduction of Glucose Oxidase by Aspergillus tubingensis CTM 507 Randomly Obtained Mutants and Study of Its Insecticidal Activity against Ephestia kuehniella

In order to enhance the production of glucose oxidase (GOD), random mutagenesis of Aspergillus tubingensis CTM 507 was performed using the chemical and physical mutagens: nitric acid and UV irradiation, respectively. The majority of the isolated mutants showed good GOD production, but only some mutants presented a significant overproduction, as compared with the parent strain. The selected mutants (19 strains), showing an overproduction larger than 200%, are quite stable after three successive subcultures. Among these, six strains revealed an important improvement in submerged fermentation. The insecticidal activity of GOD produced by the wild and the selected mutant strains was evaluated against the third larval instars of E. kuehniella. Mutant strains U11, U12, U20, and U21, presenting the most important effect, displayed an LC₅₀ value of 89.00, 88.51, 80.00, and 86.00 U/cm², respectively, which was 1.5-fold more important than the wild strain (61 U/cm²). According to histopathology observations, the GOD enzyme showed approximately similar damage on the E. kuehniella midgut including rupture and disintegration of the epithelial layer and cellular vacuolization. The data supports, for the first time, the use of GOD as a pest control agent against E. kuehniella.

Microwave Treatments of Cereals: Effects on Thermophysical and Parenchymal-Related Properties

Dielectric heating is one of the most interesting techniques for pest disinfestation. However, most of the literature works give information about the ability of microwave treatments at different power-time conditions to kill insects; less is given about the analysis of matrices structural properties and heat transport. Accordingly, the aim of this work is to investigate the effect of microwave treatments, applied for pest disinfestation, on heat transport behavior and physical/structural properties, such as water uptake capability, mineral losses, texture change, and germination capability, of most consumed cereals in human diet, such as weak wheat, durum wheat, and corn. Two different radiative treatments were performed: one in time-temperature conditions capable of inactivating the weed fauna, and the other at high temperatures of ~150 °C, simulating uncontrolled treatments. Heat transport properties were measured and showed to keep unvaried during both effective and uncontrolled microwave treatments. Instead, grain physical properties were worsened when exposed to high temperatures (reduction of germination ability and texture degradation). The achieved results, on the one hand, provide new structural and heat transport data of cereals after microwave treatments, actually not present in the literature, and on the other, they confirm the importance of correctly performing microwave treatments for an effective disinfestation without affecting matrices physical properties and nutritional features.