Ampalaya brown aphids on Pistia stratiotes

MANILA, Philippines - One month after purging of Aphid infested Ampalaya (Momordica charantia) plants, little brown aphids showed up on Cuyapo (Pistia stratiotes) or Water Lettuce. It was first thought that the brown speckles were fish food bits landing on the floating plants. After another month, the black legged brown aphids have colonized all the floaters including Limnobium (Frog bits). A few strays were found walking on Azollas and Salvinias.

High density infestations result in very unsightly plants. The Pistia started exhibiting white necrotic spots, and then the lower, older leaves turned yellow. It looks as if plants are turning old prematurely. Yellow leaves rot off resulting in reduced plant size. Plant center turned yellowish then white.

Literature search showed that there is no reported aphid infestation on floating aquarium plants much less the treatments. Application of pesticides is out of the question because pesticides will kill all the fishes in the tanks holding the Pistias (Cuyapo or Quiapo).

The highly invasive species have damaged 100% of the Cuyapo within 2 months.

Pest control  and management

As it is not practical to spray surfactants onto the plants without affecting the fishes, all the plants were skimmed off the water and dunked into strong soap solution. This resulted in almost instant death of the aphids. Total coverage of leaf surfaces is necessary. 

The plants are then washed thoroughly with clean water to eliminate the soap before reintroduction into the aquaria. Repeated spot treatment was necessary as young colonies shows up on the floating plants.

Case analysis

The exact identity of the aphids has not been established although some aphids were collected and preserved in alcohol for further Entomological studies.

The case established the fact that Water Aroids may serve as alternative host of black-legged brown aphids.

Pistia may be used in commercial rearing of predators like zigzag Lady Beetles for Integrated Pest Management programs. Young wingless colonies may be cultured separately with water as physical barrier.