Unique caveadapted planthopper

AN animal found only in an underground cave and unable to exist above ground is called a troglobite. Typical insect troglobites — which are blind, pale or white, thin and stretched out, with very long appendages — were discussed in this column last week. Such troglobites live in caves having streams and air at 100% relative humidity, and with a completely constant temperature during the day and throughout the year.

Last month, an interesting paper on a New Zealand caveadapted planthopper found only in Council Cave near Takaka, Nelson Province, was published by Dr R.L. Ferreira and colleagues in the New Zealand Journal of Zoology. This planthopper has smaller eyes than surfacedwelling relatives and is much more lightly coloured, being a creamy yellowish brown. Although its wings are reduced, it can still hop to a degree if approached.

The troglobitic plant hopper evolved over millions of years, diverging from its closest relatives to the extent that it was placed as the sole member of its own genus. It was named in 1975 as Confuga persephone (order: Hemiptera; family Cixiidae).

C. persephone feeds on surfacedwelling plants’ roots that penetrate into the furthest part of the cave. Here, there is no light, the air is at 100% relative humidity, and the constant temperature remains an invariable 11.86degC. The cave is shared with a big suite of troglobitic beetles, harvestmen, spiders, diplurans and centipedes, with which it coevolved. The cave planthopper occurs on stalactites and other secondary mineral deposits.

Ferreira and colleagues think the planthopper feeds on the roots of several species of native plants, but could not identify the host species. They provide evidence that the population is declining and is at risk of extinction if conditions change within the cave and if vegetation above the cave changes — for example, through logging, fire, or replacement of native plants with exotics. Although there is still much native vegetation above the cave and its surroundings, in places there is an influx of introduced plants such as hawthorn, barberry, banana passionfruit and blackberry.

Council Cave is rated one of New Zealand’s most biologically important caves.

1, male, and 2, female plant hopper troglobites on stalactite formations. 3, aboveground cixiid; 4, habitat deep within the cave where the caveadapted planthopper is found.