Population Dynamics of Galerucella birmanica and Its Aggregation Behavior in Brasenia schreberi Aquaculture System

Simple SummaryThe aquatic macrophyte watershield,Brasenia schreberiGmel., with its young buds coated in a thick mucilage served as a famous vegetable, has been cultivated in China for a long time. However, its production has been threatened by a pest,Galerucella birmanicaJacoby. This study investigated the population dynamics ofG. birmanicathroughout the entire growth season ofB. schreberifrom May to November and identified the aggregation behavior of the pest, with a preference for severely chewed leaf areas. Further analysis revealed that it was 2-phenylethyl isothiocyanate released from the damaged leaves that attractedG. birmanica. Our findings provide valuable insights for pest management inB. schrebericultivation fields, and the attractant effect of 2-phenylethyl isothiocyanate onG. birmanicaoffers a new perspective for the development of attractants for this insect.The aquatic vegetableBrasenia schreberiGmel. (Nymphaeales: Cabombaceae), widely cultivated in China, faces severe challenges from pest disturbances. With a field investigation,G. birmanicaoccurred for several generations in theBraseniamono-cultivation system. The first visual peak on leaf surfaces appeared in July, with eggs, larvae, pupae and adults all being recorded. The highest number of flying adults were trapped in August in reverse to the absence of beetles on leaves, followed by an extraordinary high number of eggs in September.G. birmanicaexhibited a conspicuous aggregation in distribution, with severely chewed areas having aG. birmanicaabundance 21.6 times that of the non-chewed areas. Laboratory studies with GC–MS and two-choice tests revealed four volatiles significantly discrepant in contents released from chewed/intact leaves: cis-3-hexenyl acetate (917.33 ± 29.56 vs. 604.034 ± 23.24 ng, chewed vs. intact), 2-phenylethyl isothiocyanate (595.37 ± 28.42 vs. 356.00 ± 13.44 ng), undecane (771.44 ± 34.72 vs. 1003.28 ± 47.88 ng) and methyl salicylate (1079.84 ± 49.39 vs. 532.11 ± 18.23 ng); among them, 2-phenylethyl isothiocyanate could significantly attractG. birmanicaadults. Our study suggests thatG. birmanicacan be a severe threat to mono-cultivatedB. schreberi, whereas the damaged leaves may sacrifice themselves by attracting the beetles with an herbivore-induced volatile, thus protecting the whole plant population from pest disturbance.