Study On Moth Migratory Principle Across The Bohai Strait And Flight Capacity In Mamestra Brassicae L.

The cabbage moth,Mamestra brassicae L.(Lepidoptera: Noctuidae),is a serious insect pest of vegetable crops throughout the world.Insect migration is an evolved adaptation to resources that fluctuate spatiotemporally either seasonally or less predictably,which plays an important role in their population development.However,migration might be the reason for the outbreaks of many agricultural pests.In the present paper,a long-term study on the migration of M.brassicae from April to October in 2003–2014 was carried out by means of the searchlight trapping and ovarian dissection on a small island located in the center of the Bohai Strait.Then,the flight performance of both sexes of M.brassicae moths at different ages and mating status,was examined by tethering individuals to computerized flight mills for a 24 h trial period to collect parameters on total flight distance,flight duration,and flight velocity under a laboratory condition.The main results were summarized as follows.1.A large number of M.brassicae were trapped every year on the island,which indicates that M.brassicae is a migrant and migrated at least 40–60 km across the Bohai Strait.The mean migration period of M.brassicae over the sea within a year is151 ± 8 d in 2003–2014,with the shortest time span 78 d in 2003 and the longest 189 d in 2014,respectively.The number of M.brassicae captured,however,varies considerably between months and years.2.The majority of trapped moths were females,with different levels of ovarian development and mating status in May-September 2010-2014.Most of the females trapped in May-July in 2010–2014 had relatively higher mating rate and advanced level of ovarian development.3.The mean flight velocity,duration and distance of the laboratory population of M.brassicae moths varied between ages.M.brassicae moths presented a strong flight capacity after emergence,and peaked at 2-to 3-d-old,then significantly decreased at 4-to 5-d-old.The flight capacity of females was greater than that of males.The mean flight velocity of mated moths was significant smaller than that ofvirgin moths,but there was no significant difference on the mean flight duration and flight distance between mated and virgin moths.The flight capacity of the southwardly migratory population was significantly higher than that of northwardly migratory population and transitional population collected from natural environment in Bohai Gulf.Through the above results,we know that M.brassicae is a seasonal migrant,and the over-sea migration of this species has become the regular ecological behavior.The onset of M.brassicae migration begins with sexually immature individuals,suggesting that the migration of this species does conform to the hypothesis of‘oogenesis-flight syndrome',and the development of the flight system and ovary of M.brassicae is synchronous.M.brassicae moths presented a strong flight capacity,and affected by different biological factors.Age and mating status are the key factors affect the flight capacity of M.brassicae.These findings provide a theoretical basis for the understanding of the migration behavior of M.brassicae,and are beneficial to develop forecasting systems and management strategies against this pest species.