Broflanilide reduces population growth of Helicoverpa armigera, study indicates

Parental exposure to broflanilide reduced the biological performance of the next generation of Helicoverpa armigera. The insecticide prolonged larval development, decreased survival, and reduced the fecundity of offspring. The treatment also altered the activity of detoxification enzymes and the abundance of bacterial groups in the gut. The results came from a study conducted by researchers from the Chinese Academy of Agricultural Sciences and the Sichuan Tobacco Company in China.

Researchers evaluated the lethal, sublethal, and intergenerational effects of broflanilide. The study used third-instar caterpillars of Helicoverpa armigera. The colony remained in the laboratory for more than ten generations without exposure to insecticides. The lethal concentrations used in the assays had been previously determined by the same team, with the same colony, the same instar, and the same bioassay method. The lethal concentration for 50% of the population, or LC50, was 0,457 milligrams per liter after 72 hours. The LC30 reached 0,253 milligrams per liter. The LC10 was 0,107 milligrams per liter. The toxicity ratio of 1,7 relative to a susceptible reference colony indicates that the tested population remains susceptible to the insecticide.

Reduced survival

In the parental generation, CL50 reduced larval survival from 90,80% in the control to 39%. Adult emergence fell from 100% to 78,52%. The proportion of adults with malformations reached 15,88%, compared to 5,13% in the control. Fecundity fell from 2.299,38 to 1.557,50 eggs per female. The oviposition period decreased from 12,22 to 8,06 days.

The effects persisted in the next generation, even without direct contact of the offspring with broflanilide. Parental exposure to LC50 prolonged the total larval period from 14,21 to 18,95 days. Larval survival fell from 84% to 31,19%. Adult emergence reached 59,32%. In the group originating from parents exposed to LC30, the rate was 65,28%. The control group showed 97,22%.

Changes in reproduction

Reproduction also responded to parental exposure. The fecundity of the F1 generation reached 2.117,67 eggs per female in the control group. The number dropped to 1.546 eggs after parental exposure to LC30 and to 1.243,63 eggs after LC50. LC50 also increased the occurrence of malformations among F1 generation adults to 19,77%.

Life table analysis of the F1 generation confirmed a reduction in population growth potential. The intrinsic rate of increase fell by 21,4% after parental exposure to CL30 and by 32,3% after CL50. The net reproductive rate decreased from 758,91 offspring per individual in the control group to 215,72 in CL30 and 188,63 in CL50. These reductions exceeded 70%. The average generation time reached 41,56 days in the CL50 group, compared to 35,63 days in the control group.

Detoxification systems

Broflanilide also elicited distinct responses in enzyme systems linked to detoxification. Carboxylesterase activity increased after exposure. The greatest stimulus occurred with LC10 after 24 hours, with activity approximately 3,4 times the level of the control. In the same interval, LC50 also exceeded the control, while LC30 showed no significant difference. After 72 hours, all treatments showed carboxylesterase activity above the control.

Glutathione S-transferase showed an increase in all treatments within the first 24 hours. The highest activity also occurred at CL10. After 72 hours, activity remained elevated at CL10, but decreased in treatments CL30 and CL50. In these two groups, the values ​​corresponded to 79,30% and 86,24% of the control, respectively.

The activity of cytochrome P450 monooxygenases followed the opposite direction. All treatments showed a reduction after 24 hours. At 72 hours, activity reached between 49,31% and 57,92% of the control. The researchers emphasize: changes in enzymatic activity do not prove a direct participation of these enzymes in the metabolism of broflanilide. Assays with inhibitors, gene expression, transcriptomics, or metabolomics still need to evaluate this relationship.

Gut microbiota

The study also detected changes in the gut microbiota, assessed in the CL10 and CL50 groups. In the control group, Enterococcus predominated, with a relative abundance of 92,49%. Acinetobacter accounted for 4,12%. Under CL50, Acinetobacter reached 57,73% and became dominant. The relative abundance of Enterococcus decreased. Statistical analysis identified Enterococcus as the only genus with a significant difference between CL50 and the control group.

The internal diversity of the community also responded to the treatment. The CL50 group showed a significantly higher Shannon index and a significantly lower Simpson index than the control group. This same group gathered 493 unique sequence variants, compared to 78 in the control group. However, the overall structure of the community, assessed by comparing the groups, did not show a significant difference between the treatments.

Functional prediction indicated an increase in pathways related to biodegradation and xenobiotic metabolism. The researchers themselves treat this result as an indication of functional potential, not as proof of broflanilide degradation by bacteria.

The team concluded: broflanilide can limit Helicoverpa armigera populations through direct toxicity and biological costs observed in offspring. The work considers the effects on the F1 generation as intergenerational. The research did not evaluate subsequent generations and, for this reason, does not allow classifying the effects as fully transgenerational (doi 10.3390/insects17080878).