It has been shown previously that the laticifer fluid of
Calotropis procera
(Ait.) R.Br. is highly toxic to the egg hatching and larval development of
Aedes aegypti
L. In the present study, the larvicidal potential of other laticifer fluids obtained from
Cryptostegia grandiflora
R.Br.,
Plumeria rubra
L. and
Euphorbia tirucalli
L. was evaluated. We attempted to correlate larvicidal activity with the presence of endogenous proteolytic activity in the protein fraction of the fluids. After collection, the fluids were processed by centrifugation and dialysis to obtain the soluble laticifer protein (LP) fractions and eliminate water insoluble and low molecular mass molecules. LP did not visibly affect egg hatching at the doses assayed. LP from
Cr. grandiflora exhibited the highest larval toxicity, while
P. rubra was almost inactive.
E. tirucalli was slightly active, but its activity could not be correlated to proteins since no protein was detected in the fluid. The larvicidal effects of LP from
C. procera and
Cr. grandiflora showed a significant relationship with the proteolytic activity of cysteine proteinases, which are present in both materials. A purified cysteine proteinase (papain) from the latex of
Carica papaya
(obtained from Sigma) was similarly effective, whereas trypsin and chymotrypsin (both serine proteinases) were ineffective. The results provide evidence for the involvement of cysteine proteinase activity in the larvicidal action of some laticifer fluids.
C. procera is an invasive species found in areas infested with
Ae. aegypti and thus could prove useful for combating mosquito proliferation. This is the first report to present evidence for the use of proteolytic enzymes as chemical agents to destroy
Ae. aegypti larvae.