Some ecological factors influencing the breeding success of the Brenton Blue butterfly, &lt;i&gt;Orachrysops niobe&lt;/i&gt; (Trimen) (Lepidoptera: Lycaenidae)

D.A Edge

doi:10.4102/koedoe.v45i2.24

Abstract

The Brenton Blue butterfly, Orachrysops niobe (Trimen, 1862) (Lepidoptera:Lycaenidae), is endemic to the southern Cape and is currently listed as Endangered. This study looks at some of the key ecological factors influencing the breeding success of the species—host plant abundance and condition, nectar sources, climate/ microclimate, and vegetation management techniques. The adult butterfly population was monitored over an entire breeding season; host plants were identified and individually monitored; and egg counts were done. This enabled the effects of a number of different management techniques to be evaluated (burning, cutting, physical removal of invasive elements, and combinations thereof). A fivefold increase in the population of O. niobe was observed over the breeding season. This increase was positively correlated to a similar increase in host plant abundance in the areas where cutting and physical removal of invasive elements was practiced. Burning, by contrast, appeared to have a negative impact on host plant and butterfly abundance over the same period. Impacts of other factors such as climate, nectar sources and the natural strength of the second brood are discussed. A hypothesis, of megaherbivore activity as the principal historical disturbance mechanism promoting locally favourable conditions for O. niobe to establish and maintain colonies, is proposed. Recommendations for reserve management and future research are made.

Highlights

The Brenton Blue butterfly Orachrysops niobe (Trimen, 1862) (Lepidoptera: Lycaenidae) is one of South Africa’s most threatened butterfly species, being endemic to the southern Cape and currently red-listed as Endangered (Henning & Henning 1995)
Research has been conducted on the life history (Edge & Pringle 1996; Williams 1996); butterfly population size and distribution (Britton & Silberbauer 1997); the ant populations found at the site (Robertson 1997, 1998, 2000); and on the floristics and plant communities (Lubke et al 1996)
There was a doubling of the number of host plants on the access paths, where no fire had taken place, during the observation period

Summary

Introduction

The Brenton Blue butterfly Orachrysops niobe (Trimen, 1862) (Lepidoptera: Lycaenidae) is one of South Africa’s most threatened butterfly species, being endemic to the southern Cape and currently red-listed as Endangered (Henning & Henning 1995). It is only known to occur at one locality —at Brenton-on-Sea near Knysna. The colony at Brenton-on-Sea has been subject to similar pressures but has been given a reprieve from a similar fate following a protracted and highly publicised campaign to save the species (Steenkamp & Stein 1999). This has resulted in the procurement of the land on which the colony occurs by central government and the impending proclamation of a reserve which covers 1.47 ha. Research has been conducted on the life history (Edge & Pringle 1996; Williams 1996); butterfly population size and distribution (Britton & Silberbauer 1997); the ant populations found at the site (Robertson 1997, 1998, 2000); and on the floristics and plant communities (Lubke et al 1996)

Objectives

Methods

Results

Discussion

Conclusion