Effects of carbon monoxide, nitrogen dioxide, and fine particulate matter on insect abundance and diversity in urban green spaces

The impact of three air pollutants, carbon monoxide, nitrogen dioxide, and fine particulate matter (PM(2.5)) on the diversity and abundance of insect fauna associated with Chinese thuja, Platycladus orientalis, was evaluated for the first time in Iran. Sampling was performed in Lashkar, Sadaf, and Sajjad, three urban green spaces in Mashhad, a city located in Razavi Khorasan province. A total of 29 insect species including 16 natural enemies and 13 herbivores were identified. The results indicated that herbivore abundance was positively and significantly correlated with the level of carbon monoxide and nitrogen dioxide, but not with the level of fine particulate matter. In contrast, herbivore diversity was negatively and significantly correlated only with the level of carbon monoxide. As for natural enemies, abundance and diversity both were not significantly correlated with the levels of none of all three pollutants. The aphid, Cinara thujafilina Del Guercio was the most dominant herbivore species in all the sampling sites with a relative abundance of 86% at Lashkar, 93% at Sadaf, and 95% at Sajjad. Regarding natural enemies, the ladybird, Coccinella septempunctata was the most abundant species both at Lashkar (49%) and Sadaf (35%) while the ladybird, Oenopia conglubata was the most abundant at Sajjad (21%). The highest diversity of herbivores and natural enemies across the four seasons were at the Lashkar and Sadaf sites. The results highlight that of the three air pollutants, carbon monoxide is the one that affects both on abundance and diversity of herbivore guild associated with Platycladus orientalis in urban green spaces.