Cornops aquaticum

Cornops aquaticum is a semiaquatic species of grasshopper native to the Neotropics, from southern Mexico south to central Argentina and Uruguay.^[1] It feeds and breeds exclusively on members of the aquatic plant family Pontederiaceae, especially water hyacinth (Eichhornia crassipes), and is being investigated as a possible biological pest control agent for the water hyacinth in countries where that plant is invasive.

Ecology

The female C. aquaticum inserts its ovipositor into the leaf stalk of the host plant and deposits an egg-case containing thirty to seventy eggs; the egg cases are large, measuring an average of 27 by 3 mm (1.1 by 0.1 in). The eggs hatch after about four weeks and the nymphs feed on the leaves of the plant for about seven weeks, passing through six or seven instars, and causing much damage. Adults live for up to twelve weeks; after an initial feeding period of four weeks, females deposit up to seven egg cases at intervals in the host plant tissues. Feeding trials show that besides water hyacinth, nymphs can complete their development on Pontederia cordata (pickerel weed), also in the family Pontederiaceae, and on Canna indica. In laboratory starvation trials, nymphs can also feed on some other plants but the females do not oviposit on these species and the nymphs do not develop beyond the third instar on any of them. The adults also consume large amounts of above-water foliage of their plant host and can fly vigorously between plants.^[2]

Both nymphs and adult C. aquaticum feed on the floating mats of water hyacinth (Eichhornia crassipes). Damage caused to the plant is high compared to damage caused by other grasshoppers, but nevertheless, the insect is unable to keep up with the production of new growth by the plant.^[3]

Biological control

The water hyacinth is an aquatic plant in the family Pontederiaceae whose natural enemies keep under control in its native South America. However this plant has been introduced into countries where it has insufficient natural enemies and where it has become invasive. Cornops aquaticum is under consideration as a biological control agent for this invasive plant, and has been introduced under controlled conditions into South Africa for this purpose.^[4] Before full release, the South African trials showed that, in the absence of E. crassipes, the adult insects would feed on maize (Zea mays) and sugarcane (Saccharum officinarum), but that only eggs laid on E crassipes were viable. Where the insects had a choice of diet, they invariably chose E. crassipes and were not found on the crop species.^[5]

References