Bioacoustics in population control of insects of medical importance: A review.

Vector transmitted diseases are accountable for more than 17% of all infectious disease cases worldwide according to World Health Organization. Insect vectors play a key role in transmitting diseases and loss of lives. Modified and advanced vector control strategies with chemical insecticides are needed as vectors are resistant to a particular insecticide. Moreover, chemical control is cost-inductive and may give rise to health issues. In this review, bioacoustics have been narrated as a novel technology for eco-friendly and cost-effective control of insect vectors. Many insects that rely on sounds for communication and copulation can be trapped, killed, and repelled through the mimicked sounds of conspecific males or females, generating disturbing noises. Sound can also be harnessed to prevent the mating success of insects. There is need for future studies on rejection calls and harmonic convergences in insect vectors. In-depth investigations on the higher harmonics of insect calls, along with artificial intelligence, will be beneficial for the development of successful sound- evoked control of insects of medical importance.

Ecological variations in adult life table attributes of Aedes aegypti (L.) from the desert and coastal regions of India.

The ecological variation in biological and adult life-table attributes of two populations of Aedes aegypti (Diptera: Culicidae) from the desert (Jodhpur) and coastal (Kolkata) regions of India are assessed to understand the reproductive and survival strategies. The results showed that females lived longer than males in both strains. The desert strain was more r-strategist because of its higher intrinsic rate of increase (rm  = 0.23), finite rate of increase (λ = 1.25), lower life expectancy of males (7.9 days) and females (14.4 days), mean generation time (T = 19.2 days) and doubling time (DT = 3.0 days). However, there was no difference in net reproductive rate (R0 ) between the desert and coastal strains. The coastal strain showed a longer female life expectancy (22.0 days) than the desert strain (14.4 days). However, the fecundity (eggs/female/day) was lower in the coastal strain (11.4) than in the desert strain (15.1). Conclusively, the desert (Jodhpur) strain is adapted to a better r-strategy than the coastal (Kolkata) strain of Ae. aegypti, which might be helpful to flourish in harsh environmental conditions. This study may provide accurate predictions of Ae. aegypti population dynamics for vector management.

Surveillance of mosquitoes harnessing their buzzing sound.

Mosquito surveillance for vector-borne disease management relies on traditional morphological and molecular techniques, which are tedious, time-consuming, and costly. The present study describes a simple and efficient recording device that analyzes mosquito sound to estimate species composition, male-female ratio, fed-unfed status, and harmonic convergence interaction using fundamental frequency (F0) bandwidth, harmonics, amplitude, and combinations of these parameters. The study examined a total of 19 mosquito species, including 3 species of Aedes, 7 species of Anopheles, 1 species of Armigeres, 5 species of Culex, 1 species of Hulecoetomyia, and 2 species of Mansonia. Among them, the F0 ranges between 269.09 ± 2.96 Hz (Anopheles culiciformis) to 567.51 ± 3.82 Hz (Aedes vittatus) and the harmonic band (hb) number ranges from 5 (An. culiciformis) to 12 (Ae. albopictus). In terms of species identification, the success rate was 95.32 % with F0, 84.79 % with F0-bandwidth, 84.79 % with harmonic band (hb) diversity, and 49.7 % with amplitude (dB). The species identification rate has gone up to 96.50 % and 97.66 % with the ratio and multiplication of F0 and hb, respectively. This is because of the matrices that combine multiple sound attributes. Comparatively, combinations of the amplitude of the F0 and the higher harmonic frequency band were non-significant for species identification (60.82 %). The fed females have shown a considerable increase in F0 in comparison to the unfed. The males of all the species possessed significantly higher frequencies with respect to the females. Interestingly, the presence of male-female of Ae. vittatus together showed harmonic convergence between the 2nd and 3rd harmonic bands. In conclusion, the sound-based technology is simple, precise, and cost-effective and provides better resolution for species, sex, and fed-unfed status detection in comparison to conventional methods. Real-time surveillance of mosquitoes could potentially utilize this technology.

Life table, survival and fecundity parameters of Aedes albopictus (Diptera: Culicidae) strains from desert and coastal regions of India.

The Asian tiger mosquito, Aedes albopictus (Skuse, 1895) is the anthropophilic and day-biter mosquito, residing in peridomestic habitats and is responsible for vector-borne diseases, i.e., chikungunya and dengue. The knowledge of mosquito life demographics is very important to provide a foundation for a successful vector control program. In the present study, a comparative adult life table, survival, and fecundity parameters were evaluated on desert (Jodhpur, Rajasthan) and coastal (Kolkata, West Bengal) strains of Aedes albopictus (Diptera: Culicidae) from India under the standard laboratory conditions. The results showed significant differences between these strains for the life expectancy of males, fecundity (total eggs/cohort and eggs/female life span), oviposition days, intrinsic rate of increase (rm), finite rate of increase (λ), and doubling time (DT). Female mosquitoes lived longer than the males in both strains. Significant differences were observed in the net reproductive rate (R0) between Kolkata and Jodhpur strains. The coastal (Kolkata) strain showed a longer male life expectancy (5.6 days) than the desert strain (4.0 days). However, the fecundity (eggs/female lifespan) was higher in Kolkata (360.2) than the Jodhpur strain (229.7). The Kolkata strain showed higher R0, rm, λ, and the lower T, DT than the Jodhpur strain. Conclusively, the results indicate that the coastal strain of Ae. albopictus is more r-strategist than the desert strain. This study may help in the precise prediction of Ae. albopictus population dynamics surviving in these geographical areas for vector management.

Impact of IRS: Four-years of entomological surveillance of the Indian Visceral Leishmaniases elimination programme.

BACKGROUND: In 2005, Bangladesh, India and Nepal agreed to eliminate visceral leishmaniasis (VL) as a public health problem. The approach to this was through improved case detection and treatment, and controlling transmission by the sand fly vector Phlebotomus argentipes, with indoor residual spraying (IRS) of insecticide. Initially, India applied DDT with stirrup pumps for IRS, however, this did not reduce transmission. After 2015 onwards, the pyrethroid alpha-cypermethrin was applied with compression pumps, and entomological surveillance was initiated in 2016. METHODS: Eight sentinel sites were established in the Indian states of Bihar, Jharkhand and West Bengal. IRS coverage was monitored by household survey, quality of insecticide application was measured by HPLC, presence and abundance of the VL vector was monitored by CDC light traps, insecticide resistance was measured with WHO diagnostic assays and case incidence was determined from the VL case register KAMIS. RESULTS: Complete treatment of houses with IRS increased across all sites from 57% in 2016 to 70% of houses in 2019, rising to >80% if partial house IRS coverage is included (except West Bengal). The quality of insecticide application has improved compared to previous studies, average doses of insecticide on filters papers ranged from 1.52 times the target dose of 25mg/m2 alpha-cypermethrin in 2019 to 1.67 times in 2018. Resistance to DDT has continued to increase, but the vector was not resistant to carbamates, organophosphates or pyrethroids. The annual and seasonal abundance of P. argentipes declined between 2016 to 2019 with an overall infection rate of 0.03%. This was associated with a decline in VL incidence for the blocks represented by the sentinel sites from 1.16 per 10,000 population in 2016 to 0.51 per 10,000 in 2019. CONCLUSION: Through effective case detection and management reducing the infection reservoirs for P. argentipes in the human population combined with IRS keeping P. argentipes abundance and infectivity low has reduced VL transmission. This combination of effective case management and vector control has now brought India within reach of the VL elimination targets.