Rating knockdown of flour beetles after exposure to two insecticides as an indicator of mortality

Impacts of food, temperature, and humidity on recovery in Tribolium castaneum (Coleoptera: Tenebrionidae) after exposure to a contact pyrethroid insecticide

Insects that infest postharvest commodities cause significant damage or destruction, costing billions of dollars in lost products yearly. Insecticide treatments applied as contact insecticides are effective in managing insect populations. However, recovery of the insects after exposure to these insecticides is increased if food is present, reducing the efficacy of surface treatments and leading to continued infestations. In addition, variation in temperature and humidity could play a significant role in recovery. Here, we assess the role of food, temperature, and humidity on the recovery of Tribolium castaneum Herbst, red flour beetle, after exposure to a contact insecticide. We found food is an important factor in recovery under different temperature and humidity conditions. While recovery was higher at warmer temperatures and higher humidities, recovery increased further when food was present versus absent. Moreover, we found that any amount of flour, even a dusting, resulted in over 90% of beetles recovering after insecticide exposure, but when sand was substituted for flour, recovery was 25% lower compared to a no food treatment. These results highlight the importance of how environmental factors and the availability of food influence efficacy of insecticide treatments. Sanitation in food facilities is critically important as even the smallest amount of food present can cause substantial recovery, allowing beetles to escape treated areas and move throughout facilities. Further work pinpointing variation in underlying recovery between different populations and among different insect species is needed to understand local adaptation potential.

Toxic effects of deltamethrin on oxidative stress, behavioural, organosomatic indices and histopathological changes in Digitonthophagus gazella (Coleoptera: Scarabaeinae)

Pyrethroids pose a great concern to the declining population of dung beetles and the sustainability of ecosystem services. This study aimed to investigate the toxic effects of deltamethrin on Digitonthophagus gazella. First, the LC50 value (0.275 ppm) was determined, and sub-lethal concentrations (LD; low dose-0.014ppm, MD; medium dose-0.028ppm, and HD; high dose-0.055ppm) were assessed for physiological effects. The findings showed a significant dose and time dependent increase in fluorescence intensity (DCF-DA staining) and a decrease in antioxidant activity, including superoxide dismutase (SOD), catalase (CAT), and glutathione (GSH). Furthermore, significant down regulation of cyp4g7, cyp6bq9, and cyp4q4 expression indicates enhanced oxidative stress. Additionally, a reduction in the organosomatic index, accompanied by histological changes in the brain, gut, and gonads, suggests potential functional disturbances. Overall, deltamethrin exposure had profound and irreversible pathological consequences on various vital organs and systems in D. gazella, affecting reproduction and nesting.

Exploring the efficacy of pyrethroid incorporated nets for the control of stored product moth species: immediate and delayed effects on Ephestia kuehniella and Plodia interpunctella (Lepidoptera: Pyralidae)

Insect pests pose a significant threat to stored commodities, necessitating the exploration of alternative pest management strategies. Long-lasting insecticide-incorporated nets (LLINs) have emerged as a promising tool, offering selectivity and reduced ecological impact compared to conventional chemical approaches. However, their efficacy against Ephestia kuehniella Zeller and Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae), cosmopolitan stored product moth species, has remained underexplored. This study investigated the immediate and delayed effects of 2 commercial pyrethroid-incorporated nets, Carifend (0.34% α-cypermethrin) and D-Terrence (0.4% deltamethrin), on the adult and larval stages. Both LLINs demonstrated high efficacy in controlling E. kuehniella and P. interpunctella, with mortality rates reaching up to 100% depending on exposure and post-exposure durations. Particularly, rapid knockdown was observed with D-Terrence net inducing 100% of adults in P. interpunctella after 30 min exposure. LLINs achieved almost 100% immediate mortality rate against adults after just 1 day of exposure. In addition, immediate rates of affected individuals reached as high as 81% and 91% in E. kuehniella and P. interpunctella larvae, respectively, following just 5 h of exposure to the D-Terrence. Different responses were observed between the adult and larval stages, with larvae exhibiting higher tolerance and potential for recovery from the affected phase after short exposures. There were increasing mortality rates after greater exposure to LLIN. Findings highlight the potential of LLINs as a pest management tool in storage facilities against these important stored product moths. Understanding the responses between life stages and the significance of delayed effects is crucial for optimizing LLIN deployment strategies.

Synthesized peptide analogs from Eumenes pomiformis (Hymenoptera: Eumenidae) venom reveals their antibiotic and pesticide activity potential

One natural antimicrobial peptide (EpVP2a, Eumenes pomiformis Venom Peptide 2a) found in the venom of a potter wasp (Eumenes pomiformis) and six analogs were synthesized and tested to compare their antimicrobial, antifungal, pesticide, and hemolytic activity with the wild type. Our results indicated that while the original peptide and the synthetic analogs had no antifungal activity or anti-bacterial activity against Pseudomonas aeruginosa, the original peptide and the analog with substitution of the aspartic acid on the sequence by a lysine (EpVP2a-D2K2) had activity against Escherichia coli, Staphylococcus aureus and Bacillus subtilis. This same analog also shows significant insecticide activity. The analog with substitution of lysine with a slightly smaller ornithine had activity against E. coli and B. subtilis. All analogs show low hemolytic activity compared to the natural peptide. The peptide with a reverse sequence to the natural one (EpVp2a Retro) shows low helix structure which can also explain why it has no antibacterial activity and low hemolytic activity. Circular dichroism spectra show that these peptides form an alpha helix structure and their amino acid positions predict an amphipathic nature.

Insecticide susceptibility status of Anopheles gambiae (s.l.) in and surrounding areas of Lake Tana, northwest Ethiopia

BACKGROUND

Vector control is the most effective malaria control and prevention measure. Among these, IRS and LLINs are the most important chemical insecticide interventions used in malaria prevention and control strategies in Ethiopia. However, the long-term effectiveness of these strategies is under threat due to the emergency and spread of insecticide resistance in the principal malaria vector. Therefore, this study was carried out, under standardized laboratory conditions to assess the killing effect of some insecticides against An. gambiae s.l.

METHODS

Mosquitoes in late instar larvae and pupae stages were collected from different breeding habitats of the study sites using a soup ladle (350 ml capacity). The immature was reared to adults at optimum temperature and humidity in a field insectary using the WHO protocol. Four insecticides representing three chemical classes were used against adult mosquitoes. These were permethrin, deltamethrin, pirimiphos-methyl and bendiocarb. Susceptibility tests were carried out from September to December 2021 using the WHO standard procedures. Mortality rate, variation, interaction effect and knockdown times (KDT50 and KDT95%) were computed using descriptive statistics, multivariate analysis of variance and log-probit regression model using SPSS version 20 software.

RESULTS

Totally, 1300 Anopheles gambiae s.l. were tested to determine the susceptibility status to the four insecticides. Among these, 90.7% of them were susceptible to insecticides, whereas the remaining 9.3% of specimens were resistant to the insecticides. The results of the analysis of variance showed that mortality significantly varied between insecticides (F = 26.06, DF = 3, P < .0001), but not between study locations (F = 1.56, DF = 3, P = 0.212). On the other hand, the mean comparison of dead mosquitoes showed some signs of interaction between bendiocarb and locations, but not other insecticides and locations.

CONCLUSIONS

This study revealed that the knockdown times and effectiveness of different insecticides varied in different study sites. Therefore, insecticide resistance information is very essential for concerned bodies to make informed and evidence-based decisions on vector control.