Chemical ecology and toxicology of venom alkaloids in red imported fire ant (Solenopsis invicta) and tropical fire ant (S. geminata) in Taiwan
Date Issued
2009
Date
2009
Author(s)
Lai, Li-Chuan
Abstract
The red imported fire ant (RIFA), Solenopsis invicta was first discovered in Taiwan in 2003, and both monogyny and polygyny were characterized simultaneously. The tropical fire ant (TFA), Solenopsis geminata was introduced into southern Taiwan many years ago and has continued to threaten the residents. Fire ant venom contains about 90% to 95% water insoluble alkaloids and a small amount of protein. The alkaloids exhibit antibacterial, hemolytic, insecticidal and histamine-releasing properties, whereas the four major protein allergens in the worker venom are responsible for anaphylactic reactions. Because of both monogyne and polygyne colonies of S. invicta now occupy Taiwan, the venom alkaloids from workers of both social forms in S. invicta and from workers in S. geminata were investigated. The venom alkaloids were studied by gas chromatography coupled to mass spectrometry (GC-MS). Six major venom alkaloids were detectable in both social forms of workers of S. invicta and two major venom alkaloids were detectable in workers and soldiers of S. geminata. The sum of proportions of unsaturated alkaloids from polygyne workers was significantly higher than that from monogyne workers of S. invicta, regardless of rearing temperatures, sampling seasons or geographic locations. Both C13:C13:1 and C15:C15:1 ratios in alkaloid venom of monogyne workers were statistically higher than that of polygyne workers. All examined nests of S. geminata collected from central Taiwan (Taichung City and Changhua County) and southern Taiwan (Tainan City) represent monogyne form only. The results also revealed that the ratio of cis C11 to trans C11 alkaloids in soldiers was significantly higher than that in workers of S. geminata. There was no statistically significant difference on the relative alkaloids content and the ratio of cis C11 to trans C11 alkaloids in venom while workers were reared at four temperature conditions. Nevertheless, the ratio of cis C11 to trans C11 alkaloids in the venom of workers was the highest in spring and lowest in winter. Our results showed that the head length, head width, abdomen length, body length and venom volume differed significantly between soldiers and workers of S. geminata. Furthermore, the head length, head width, abdomen length and body length were positively correlated with venom volume in soldiers and workers of S. geminata. The third to fourth instar larvae of Plutella xylostella and the third instar larvae of Spodoptera litura were treated with fire ant’s venom. The diamondback moth larva which treated with venom became black, paralysis and died after 24 hours. The sections of larvae of diamondback moth indicated that cells lyse and the accumulation of melanins. Fire ant venom-induced symptoms in Sp. litura larvae include contractile, flaccid paralysis and edema. The order of toxicity of fire ants venom was TFA > RIFA (M) > RIFA (P). The venoms from these fire ants are complex cocktail, which evolved for the purpose of killing or paralyzing prey. The objective of toxicity of fire ant venom toward the P. xylostella and Sp. litura larvae was to understand the effects of venom on agricultural ecology.
Subjects
Solenopsis invicta
Solenopsis geminata
venom alkaloids
unsaturated alkaloids
Plutella xylostella
Spodoptera litura
melanin
Type
thesis
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