Insect Herbivores Associated with Lycium Ferocissimum (Solanaceae) in South Africa and Their Potential As Biological Control Agents in Australia
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Insect herbivores associated with Lycium ferocissimum (Solanaceae) in South Africa and their potential as biological control agents in Australia § L.D. Chari1* , E.V. Mauda2 , G.D. Martin1 & S. Raghu2 1Centre for Biological Control, Department of Zoology and Entomology, Rhodes University, Makhanda, 6400 South Africa 2CSIRO, Ecosciences Precinct, GPO Box 2583, Brisbane, Queensland, 4001 Australia Lycium ferocissimum Miers (Solanaceae) is an indigenous shrub in South Africa but has become invasive in several countries including Australia, where chemical and mechanical control methods have proved costly and unsustainable. In Australia, biological control is being considered as a management option, but the herbivorous insects associated with the plant in its native range are not well known. The aim of this study was to survey the phytophagous insects associated with L. ferocissimum in South Africa and prioritise promis- ing biological control agents. In South Africa, the plant occurs in two geographically distinct areas, the Eastern and Western Cape provinces. Surveys for phytophagous insects on L. ferocissimum were carried out repeatedly over a two-year period in these two regions. The number of insect species found in the Eastern Cape Province (55) was higher than that in the Western Cape Province (41), but insect diversity based on Shannon indices was highest in the Western Cape Province. Indicator species analysis revealed eight insect herbivore species driving the differences in the herbivore communities between the two provinces. Based on insect distribution, abundance, feeding preference and available literature, three species were prioritised as potential biological control agents. These include the leaf-chewing beetles Cassida distinguenda Spaeth (Chrysomelidae) and Cleta eckloni Mulsant (Coccinel- lidae) and the leaf-mining weevil Neoplatygaster serietuberculata Gyllenhal (Curculionidae). Key words: invasive plants, weed biocontrol, native range surveys, phytophagous insects, agent prioritisation. INTRODUCTION Many weed biological control programmes have boxthorn, is a woody plant belonging to the been based on limited and ad hoc surveys that Solanaceae family that includes several important considered only the most damaging and abun- agricultural and environmental species (Haegi dant insect species, often resulting in mixed out- 1976; Arnold & Wet 1993). The genus Lycium L. comes (Goolsby et al. 2006). Biological control consists of small to large shrubs with a wide distri- programmes can be greatly facilitated by a com- bution in arid to semi-arid and temperate to sub- prehensive understanding of the natural enemies tropical regions of the world (Minne et al. 1994). associated with the target plant in its region of Although L. ferocissimum is indigenous to the origin (Syrett et al. 2000; Goolsby et al. 2006). Western and Eastern Cape provinces of South Having an extensive suite of potential agents to Africa (Arnold & Wet 1993; Venter 2000), the choose from allows researchers to make informed species comprises two distinct populations that decisions about the most appropriate agent for the are separated by a 200 km geographic barrier, target weed, ultimately reducing the risk of intro- comprising a combination of the Cape Fold Moun- ducing unsuitable, ineffective agents (Balciunas tains and the Knysna Forest (Fig. 1; Venter 2000). 2004; Goolsby et al. 2006). Such a focus on agent As a result of the plant’s ability to grow in diverse prioritisation/selection is increasingly being advo- environments, it has become invasive in some cated and practised in weed biological control countries. (Morin et al. 2009). In the 19th century, L. ferocissimum was used in Lycium ferocissimum Miers, known as African Australia as a hedge plant and wind-break but has *Author for correspondence. E-mail: [email protected] Received 25 November 2019. Accepted 2 March 2020 ISSN 1021-3589 [Print]; 2224-8854 [Online] African Entomology 28(2): 00–00 (2020) DOI: https://doi.org/10.4001/003.028.0000 ©Entomological Society of Southern Africa 2 African Entomology Vol. 28, No. 2, 2020 Fig. 1. Surveyed Lycium ferocissimum sites (l) in the geographically distinct Eastern (EC) and Western (WC) Cape provinces of South Africa (SANBI; Venter 2000). The two populations are separated by a 200 km geographic barrier consisting of a combination of the Cape Fold Mountains and the Knysna Forest. The hypothesised distribution of the two populations was projected (red and blue circles) using the furthest apart points (sites) to determine the diameter. See supplementary figure (Fig. S1) for all known localities of the plant from herbarium records. since spread outside its propagated range, where nation of management strategies (Noble & Rose it outcompetes local plant species (Noble & Adair 2013; Noble & Adair 2016). To facilitate the weed’s 2016). Lycium ferocissimum is widespread in several management, a biological control programme Australian states, including New South Wales, against L. ferocissimum was initiated in Australia in South Australia, Tasmania and Victoria, with 2016. An Australian project, funded by the Austra- restricted distributions in Queensland and West- lian Government’s Department of Agriculture and ern Australia, and extremely restricted distribu- Water Resources, sought the services of Rhodes tions in the Northern Territory. Due to its exten- University, Centre for Biological Control, to pro- sive environmental and economic damage, it vide assistance to The Commonwealth Scientific was declared a ‘Weed of National Significance’ in and Industrial Research Organisation in Australia Australia in 2012 (Australian Government 2013). by conducting surveys for natural enemies of Lycium ferocissimum has also become an invasive L. ferocissimum in its native range, South Africa. weed in New Zealand, where it is restricted to This study aimed to identify the herbivorous coastal areas of the South and North Islands insect fauna associated with the plant’s two popu- (Haegi 1976; Webb et al. 1988; Kriticos et al. 2010; lations in the Eastern and Western Cape provinces Adair 2013). In Australia, despite chemical and of South Africa. In addition to cataloguing the mechanical control efforts, the weed continues to insect herbivores, comparisons were made between expand its distribution into new areas (Julien 2006; the Eastern and Western Cape populations of Noble & Rose 2013). Due to its capacity to regener- L. ferocissimum to test for any differences in insect ate from root stocks, stems and seeds, successful herbivore species richness, diversity and commu- control of the weed will probably require a combi- nity composition. These analyses, combined with Chari et al.: Insect herbivores as biological control agents of Lycium ferocissimum in Australia 3 information on host-specificity, were used to to beat the branches above the tray to knock off all prioritise species that warrant further investiga- insects. Beating was carried out for 5 min at each site. tion as potential biological control agents. All insects were collected and placed in killing bottles charged with ethyl acetate. Insects were METHODS then preserved in 70 % alcohol or pinned. Using identification guides (e.g. Scholtz & Holm 1985; Site determination Picker et al. 2004), insects were identified to the The coordinates for localities known to have had lowest possible taxonomic level and then sent to L. ferocissimum (its natural distribution) were the Biosystematics Division of the Plant Health & obtained from South African herbarium records, Protection Research Institute (Agricultural Research the South African National Biodiversity Institute Council, South Africa) for confirmation of identity. online database (SANBI 2016) and available litera- ture. Sample sites within the two distributio- Data analysis nal ranges were then located during roadside To establish sampling representativeness and surveys, from which a total of 53 sites were sur- adequacy, a sample-based rarefaction (accumula- veyed. At each sampling event, an individual of tion) curve was compiled from the abundances of the L. ferocissimum population was tagged and its insect species collected during each sampling GPS coordinates recorded (see supplementary occasion, using the software EstimateS 9 (Colwell Tables S1–S2). 2005). The rarefaction curve was created using the analytically calculated Sest (number of species Insect surveys expected; Mao Tau). The non-parametric Michae- Native range surveys for phytophagous insects lis-Menten (MMMean) estimator and the inci- on L. ferocissimum were carried out over a two-year dence-based coverage estimator (ICE) were used period, between 2017 and 2018, in both provinces. to evaluate sample size adequacy (Chazdon et al. To account for seasonal variations, collections 1998; Toti et al. 2006). When the observed rarefac- were made during different times of the year, at tion curve (Sest) and the estimators (MMMean and least twice during both the winter (June–August) ICE) converge closely at the highest observed rich- and summer (October–February) months, and ness, the richness estimates can be considered once during the autumn (March–May) and spring representative (Longino et al. 2002). Insect species (October) months. Searches were timed to ensure that were encountered only once were not uniformity across all sites, with three researchers included in the analyses. searching for 5 min each. Leaves were scrutinised To investigate the differences in herbivore for both ectophages and endophages,