It seems that the only practical remedy for all the above is a systemic
insecticide, applied once or twice a year. Application is preferential
when the plants are given their long awaited drenching in the warm season.
Koringkriek (Insecta: Family Tettigoniidae)
It is commonly believed that the greatest natural predator is the
koringkriek (translated=wheatcricket), which is common in the
arid areas
in which lithops are encountered.
These not only eat the exposed lobes of the plant, but also the seed
capsules. In this way potential future generations are lost.
Koringkriek's are not related to crickets, but to locusts,
such
as this superbly camouflaged toad grasshopper.
Koringkriek illustration
Koringkriek photograph 1(from Rhodes University
insect collection)
Koringkriek photograph 2
Koringkriek damage to L.julii
Ground squirrel
From what farmers have made us believe, the erdmannetjie
(translated=small earth man) has the most profound visual effect
on colonies they forage from, especially in times of drought.
They dig the plant out leaving only the old dried shells and seed capsules
behind. A colony can be dotted with hundreds of these small excavations
, but as the seeds are not consumed, the potential for future
generations remains.
Ground squirrel picture
Porcupine
According to farmers in the L.hallii and L.hookeri areas, porcupines
or ystervarke(translated=ironpig)(Hystrix africaeaustralis)
frequently eat the plants whole. These are speculations and remain to be
proven.
Porcupine picture
Various Rodentia
No study has been conducted on this matter, but it is presumed that a
number of rodents also attack lithops especially in times of drought.
This is potentially advantageous as a method of dispersal, as the seeds
are defecated elsewhere.
Farm stock
A number of ruminants, when forced to be resourceful in times of hardship,
will occasionally crop off the aboveground portion of the body.
This does not affect reproduction in any manner. The damage is usually only
cosmetic as the body is replaced the following
season. The only other known damage is from stock trampling and urination
on colonies.
Grubs
One colony we visited had grubs within the plant bodies, seemingly happy
to devour the plant from within, avoiding detection in all manner, other
than the slightly unhappy looking plant. The grubs we assume to be
Lepidopteran (butterflies and moths) larvae of some sort, but have not
been able to find any further information on the subject.
Illustration of a Lepidopteran grub
Man
Probably the most worrying damage and cause of extinction of many a
colony has come from man's activities in the form of overzealous
collectors, the construction of dams, roads and the spread of urban and
rural development. This is sadly reflected in a renown scientists
description of Homo sapiens as a terminator species. Our earth's
fifth great extinction is by many believed will be catalysed by man and
will be the first extinction caused by a lifeform rather than natural
events.
Birds
Many a bird has flown into our hothouse and taken a chunk out of our
lithops' heads, but it seems the plants do not meet their taste expectations
, and they never return. Once again no permanent damage is done.
Mealy-bug(Insecta: Family Pseudococcidae)
I am sure that many gardeners are familiar with the persistent mealy-bug.
These have been the major pest of certain of our succulents especially
Stapeliads, but they have taken to the odd lithops or two, harming the
new generations body before it is visible.
Mealy-bug illustration
Root-aphid(Insecta: Family Aphididae)
This has proven to be a more persistent and problematic pest, as you are
not aware of their presence. Only when repotting do you see evidence of
them on the roots, in the form of small white balls of fluff. If the small
white nests are probed with forceps, the root-aphids become visible.
They tend to appear like small mealy-bugs.
Earwigs(Insecta: Family Forficulidae)
These insects are ever present among our lithops. Often they are found in
the fissure of the plant, but thus far we have not been able to pinpoint
the possible damage they may cause. It is, however, known that certain
families of earwigs are phytophagous(planteaters).
Earwig illustration
Mealy-bugs are best treated the moment an infestation is detected.
Broad spectrum aerosol insecticides we have been found to be useful.
Alternatively the mealy-bug can be removed by hand and the plant checked
approximately 10 days later, as this is the time taken for the eggs to
hatch.
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