The dragonflies and damselflies have started laying eggs before the onset of winter, which will put them in hibernation, says Faiyaz Khudsar, lead scientist in charge of the week-long survey of the odonata species.
Erratic rainfall over the past week has caused them to misinterpret the weather and thereby alter their life cycle.
Speaking to Business Standard, Khudsar, an entomologist, said the survey has found only 25 of the recorded 47 species from the Zoological Survey of India 1997, which is the base figure.
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The survey has found that the maximum number of individual odonates in the Kalindi Biodiversity Park to be about 3,348 from 12 species. The Tughlaqabad Biodiversity Park has reported 81 odonates from seven species.
The report also observed that due to the higher water temperatures, the larvae developed more quickly. And, this has led to developing shorter wings compared to their body size.
“As the relative wing size decreases, they will experience a higher wing load, making them less dispersal. Hence, it will affect their ability to move around and predate harmful pests, including mosquitos,” says the report.
The report also states that dragonflies generally have a short life span of about a few weeks only. So, the unfavourable conditions they face can reduce their chances of successful reproduction and also cause direct mortality.
Due to the deficit monsoon last year, the number of dragonflies and damselflies has dwindled.
“The rains were very less this year and erratic due to which water around some perennial seasonal wetlands may have reduced. This, in turn, might have reduced the controlling agents (of mosquitoes). Due to the erratic rainfall, the odonates might not have got a chance to breed properly,” said Khudsar.
“Since these insects require stable oxygen levels and clean water, scientists consider them as reliable bioindicators of the health of an ecosystem. They play a significant role in controlling the insect population, especially mosquitoes and agricultural pests. A single dragonfly can reportedly eat 30-100 mosquitoes per day,” says the report.
Speaking to Business Standard, Khudsar also noted that the dwindling odonates can also affect their predators. These are birds like Heron and Shikra, which feed on the dragonflies.
He also noted that one particular dragonfly — which was abundant in the Yamuna Biodiversity Park and commonly called picture wing — has shifted its habitat to the Aravalli Biodiversity Park. Aravalli has recorded 555 dragonflies from 12 species.
According to the report, an exercise to assess species diversity and density of dragonflies and damselflies this year was undertaken in all the seven biodiversity parks during September 19-25.
Citizens, students from Hansraj College, Amity University and Jamia Millia Islamia participated in this exercise. It was under the guidance of scientists and staff of biodiversity parks.
The survey of odonates hasn’t been conducted regularly over the years.
A previous such attempt was made in 2018 by three biodiversity parks namely, Yamuna, Neela Hauz and Tilpath Valley. From there, 25, nine and five species were found, respectively.