Biology and conservation of the threatened Karkloof blue butterfly Orachrysops ariadne (Butler) (Lepidoptera: Lycaenidae)
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Date
2002
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Abstract
The Karkloof blue butt erfly, Orachrysops ariadne (Butler), is endemic to the
Mistbelt grassland of KwaZulu-Natal province, South Africa, and is currently
Red-listed as 'Vulnerable' . O. ariadne is univoltine and on the wing in March and April, when it utilizes eight species of nectar plants. This study confirmed that the
larval hostplant is Indigofera woodii H. Bol. var. laxa H. Bol., an erect variety. It was
also confirmed that this butterfly is ant-dependent, with the young larva being taken
into the nest of Camponotus natalensis (F. Smith) where development continues, including pupation.
This study compares the ecological conditions at the four known locations so as to
make informed decision s regarding its conservation. A large proportion of the
grassland in KwaZulu-Natal has been aforested and cultivated, and at least 92% of the
Mistbelt has been transformed, with only about 1% in good condition remaining.
Predictions on the habitat and habit at requirements of this species are necessary for
developing a conservation strategy and action plan. Here , we propose O. ariadne as
an indicator species for Mistbelt grass land. Saving enough of the remaining Mistbelt
grassland is crucial, not just for the survival of the Karkloof blue, O. ariadne, but also
for the Mistbelt grassland community as a whole.
The population structure and movement of Orachrysops ariadne and O. subravus
were studied by mark-release-recapture methods in 1999. There were 290 O. ariadne
marked over 48 days between March and April, 124 (42 .8%) were recaptured at least
once. Of 631 O. subravus marked over two months between September and
November, 311 (49 .3%) were recaptured at least once. Both species exhibited
protandry, male appearance about one to two weeks earlier. The sex ratio of O.
ariadne is heavily male biased 5.6 :1 (246 males and 44 females), and the sex ratio of
O. subravus is 1.6:1 (387 males and 244 females). The Jolly-Seber model was used to estimate daily population numbers (N ᵢ), survival rates (Ø ᵢ), recruitment rates (B ᵢ),
proportion of marked animals in the total population (α ᵢ ), and the number of marked
animals at risk (M ᵢ) . Average residence times of male adults were generally similar in
both species in the range of 5.36-5.44 days, and were slightly longer for male than for
female O. subravus (by 4.09 days). 0. ariadne is a strong and rapid back and forth
flier, covering mean recapture distances of 157 m, almost twice that of 0. subravus,
principally in search of scarce nectar sources. The extreme rarity of 0. ariadne is not
so much to do with behaviour, survivorship or longevity, but rather the butterfly is
limited in distribution by suitable habitat for both larva and adult.
The aim of management is to optimize the habitat so that it best meets the present
and future needs of the butterfly. The effects of the current fire regime on the butterfly,
host plant and ant host were evaluated here. It is recommended that burning only take
place after the larvae have hatch ed and gone underground with the ant host. Using
GPS and GIS, core, quality habitat characteristics were defined. In cooperation with
the landowner at one site, alien invasive plants are being removed to increase the area
of quality habitat. Availability of host plants is limiting for success of the butterfly in
the field. Guidelines are provided for propagation and introduction of the host plant, so as to provide the butterfly with more oviposition sites.
Description
Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 2002.
Keywords
Lepidoptera., Endangered species--KwaZulu-Natal., Endangered species--South Africa., Butterflies--KwaZulu-Natal., Butterflies--South Africa., Theses--Entomology.