Studies on population dynamics and regulatory factors (biotic vs. abiotic and bottom-up vs. top-down) of the pest species belonging to genera Helicoverpa and Heliothis (Lepidoptera: Noctuidae) on cotton, chickpea and tomato

In the present study, the populations of Helicoverpa armigera, Heliothis peltigera and Heliothis viriplaca were monitored under field conditions on cotton, tomato and chickpea in different parts of Iran (Central Khorasan, Golestan, Khuzestan, Lorestan, Markazi, North Khorasan, Tehran and West Azerbaijan provinces) during 2007-2009 growth seasons. The results showed that the adult and larva populations were highly correlated. Based on light-trap data, H. armigera and H. peltigera were captured in all the crops and most of the sites. On the contrary, H. viriplaca was captured only on chickpea. In total, 2175 adults were captured from 33 field-seasons with a relative abundance of 0.44, 0.32 and 0.24 for H. armigera, H. peltigera and H. viriplaca, respectively. When overall populations were compared, H. armigera showed to be a predominant species. The mean H. armigera adults captured per field-season were 31.3, 38.6 and 11.6 on cotton, tomato and chickpea, respectively. These figures were 32.3, 25.9 and 7.5 for H. peltigera, and 0.1, 0.1 and 51.0 for H. viriplaca. Based on the weekly mean of adult catch, H. armigera and H. peltigera showed similar population behaviour. These two species seem to cause damages on all studied crops, but the highest damage would happen on cotton and tomato. On the contrary, H. viriplaca proved to be a specific pest on chickpea and other leguminoses. The decreasing trends in adults (all species together) captured during studied years (the relative abundances of 0.40, 0.32 and 0.28 for the 1st, 2nd and 3rd years, respectively) might be due to climate changes such as cold winter in 2007 and drought in following years. However, the increasing trend in H. viriplaca adults during studied years suggests that this species possesses differential biological characteristics compared to the two others. In addition, more variability in H. viriplaca populations compared with other species may be because of its limited host range and distribution. These findings bring it to mind that further studies are required to determine ecological factors influencing population changes of these species.