The suitability of non-target native mangroves for the survival and development of the lantana bug Aconophora compressa, an introduced weed biological control agent

Aconophora compressa (Hemiptera: Membracidae), a biological control agent introduced against the weed Lantana camara (Verbenaceae) in Australia, has since been observed on several non-target plant species, including native mangrove Avicennia marina (Acanthaceae). In this study we evaluated the suitability of two native mangroves, A. marina and Aegiceras corniculatum (Myrsinaceae), for the survival and development of A. compressa through no-choice field cage studies. The longevity of females was significantly higher on L. camara (57.7 ± 3.8 days) than on A. marina (43.3 ± 3.3 days) and A. corniculatum (45.7 ± 3.8 days). The proportion of females laying eggs was highest on L. camara (72%) followed by A. marina (36%) and A. corniculatum (17%). More egg batches per female were laid on L. camara than on A. marina and A. corniculatum. Though more nymphs per shoot emerged on L. camara (29.9 ± 2.8) than on A. marina (13 ± 4.8) and A. corniculatum (10 ± 5.3), the number of nymphs that developed through to adults was not significantly different. The duration of nymphal development was longer on A. marina (67 ± 5.8 days) than on L. camara (48 ± 4 days) and A. corniculatum (43 ± 4.6 days). The results, which are in contrast to those from previous glasshouse and quarantine trials, provide evidence that A. compressa adults can survive, lay eggs and complete nymphal development on the two non-target native mangroves in the field under no-choice condition.

Factors influencing the release and establishment of weed biological control agents

Mike Day and colleagues recently published their paper 'Factors influencing the release and establishment of weed biocontrol agents' in Proceedings of the 16th Australian Weeds Conference. The CRC for Australian Weed Management facilitated an investigation into the factors influencing the release and establishment of weed biological control agents on a wide variety of Australian weeds. The investigation improved the understanding of post-release ecology of biocontrol agents and generated recommendations for best practice. Factors affecting successful establishment on the weed include host plant characteristics, size of releases, dispersal power of the agent, predation and parasitism, and climate. A best practice guide was produced by the CRC to assist practitioners in designing robust release strategies to increase rates of establishment.

Review of approaches to evaluate the effectiveness of weed biological control agents

We review key issues, available approaches and analyses to encourage and assist practitioners to develop sound plans to evaluate the effectiveness of weed biological control agents at various phases throughout a program. Assessing the effectiveness of prospective agents before release assists the selection process, while post-release evaluation aims to determine the extent that agents are alleviating the ecological, social and economic impacts of the weeds. Information gathered on weed impacts prior to the initiation of a biological control program is necessary to provide baseline data and devise performance targets against which the program can subsequently be evaluated. Detailed data on weed populations, associated plant communities and, in some instances ecosystem processes collected at representative sites in the introduced range several years before the release of agents can be compared with similar data collected later to assess agent effectiveness. Laboratory, glasshouse and field studies are typically used to assess agent effectiveness. While some approaches used for field studies may be influenced by confounding factors, manipulative experiments where agents are excluded (or included) using chemicals or cages are more robust but time-consuming and expensive to implement. Demographic modeling and benefit–cost analyses are increasingly being used to complement other studies. There is an obvious need for more investment in long-term post-release evaluation of agent effectiveness to rigorously document outcomes of biological control programs.

Predicting population dynamics of weed biological control agents: science or gazing into crystal balls?

Various factors can influence the population dynamics of phytophages post introduction, of which climate is fundamental. Here we present an approach, using a mechanistic modelling package (CLIMEX), that at least enables one to make predictions of likely dynamics based on climate alone. As biological control programs will have minimal funding for basic work (particularly on population dynamics), we show how predictions can be made using a species geographical distribution, relative abundance across its range, seasonal phenology and laboratory rearing data. Many of these data sets are more likely to be available than long-term population data, and some can be incorporated into the exploratory phase of a biocontrol program. Although models are likely to be more robust the more information is available, useful models can be developed using information on species distribution alone. The fitted model estimates a species average response to climate, and can be used to predict likely geographical distribution if introduced, where the agent is likely to be more abundant (i.e. good locations) and more importantly for interpretation of release success, the likely variation in abundance over time due to intra- and inter-year climate variability. The latter will be useful in predicting both the seasonal and long-term impacts of the potential biocontrol agent on the target weed. We believe this tool may not only aid in the agent selection process, but also in the design of release strategies, and for interpretation of post-introduction dynamics and impacts. More importantly we are making testable predictions. If biological control is to become more of a science making and testing such hypothesis will be a key component.

The status of weed biological control in Vanuatu

Biological control of weeds in Vanuatu began in 1935, with the introduction of the tingid Teleonemia scrupulosa to control Lantana camara. To date, nine biological control agents have been intentionally introduced to control eight weed species. Seven of these agents have established on their respective hosts while an eighth, Zygogramma bicolorata, an agent for Parthenium hysterophorus has only recently been released and establishment is unlikely. The fate of a ninth agent, Heteropsylla spinulosa, released for the control of Mimosa diplotricha is unclear. Six other biological control agents, including Epiblema strenuana which was first detected in 2014 on P. hysterophorus on Efate have spread into the country unintentionally. Control of the target weeds range from inadequate to very good. By far the most successful agent has been Calligrapha pantherina which was introduced to control Sida acuta and Sida rhombifolia. The beetle was released on 14 islands and managed to spread to at least another 10 islands where it has effectively controlled both Sida spp. Control of the two water weeds, Eichhornia crassipes by Neochetina bruchi and N. eichhorniae and Pistia stratiotes by Neohydronomus affinis, has also been fairly good in most areas. Two agents, T. scrupulosa and Uroplata girardi, were released on L. camara, and four other agents have been found on the weed, but L. camara is still not under adequate control. The rust Puccinia spegazzinii was first released on Mikania micrantha in 2012 and successfully established. Anecdotal evidence suggests that it is having an impact on M. micrantha, but detailed monitoring is required to determine its overall impact. Future prospects for weed biological control in Vanuatu are positive, with the expected greater spread of recently released agents and the introduction of new agents for P. hysterophorus, L. camara, Dolichandra unguis-cati and Spathodea campanulata.

Pre-release evaluation of the efficacy of the leaf-sucking bug Carvalhotingis visenda (Heteroptera: Tingidae) as a biological control agent for cat's claw creeper Macfadyena unguis-cati (Bignoniaceae)

In classical weed biological control, assessing weed response to simulated herbivory is one option to assist in the prioritization of available agents and prediction of their potential efficacy. Previously reported simulated herbivory studies suggested that a specialist herbivore in the leaf-feeding guild is desirable as an effective biological control agent for cat's claw creeper Macfadyena unguis-cati (Bignoniaceae), an environmental weed that is currently a target for biological control. In this study, we tested (i) whether the results from glasshouse-based simulated herbivory can be used to prioritise potential biological control agents by evaluating the impact of a leaf-sucking tingid bug Carvalhotingis visenda (Drake & Hambleton) (Hemiptera: Tingidae) in quarantine; and (ii) the likely effectiveness of low- and high-densities of the leaf-sucking tingid after its release in the field. The results suggest that a single generation of C. visenda has the potential to reduce leaf chlorophyll content significantly, resulting in reduced plant height and leaf biomass. However, the impact of one generation of tingid herbivory on below-ground plant components, including the roots and tuber size and biomass, were not significant. These findings are consistent with results obtained from a simulated herbivory trial, highlighting the potential role of simulated herbivory studies in agent prioritisation.

A systematic approach to biological control agent exploration and prioritisation for prickly acacia (Acacia nilotica ssp. indica)

Agent selection for prickly acacia has been largely dictated by logistics and host specificity. Given that detailed ecological information is available on this species in Australia, we propose that it is possible to select agents based on agent efficacy and desired impact on prickly acacia demography. We propose to use the 'plant genotype' and 'climatic' similarities as filters to identify areas for future agent exploration; and plant response to herbivory and field host range as 'predictive' filters for agent prioritisation. Adopting such a systematic method that incorporates knowledge from plant population ecology and plant-herbivore interactions makes agent selection decisions explicit and allow more rigorous evaluations of agent performance and better understanding of success and failure of agents in weed biological control.

Temporal patterns in incidence and abundance of Aconophora compressa (Hemiptera: Membracidae), a biological control agent for Lantana camara, on target and nontarget plants

The membracid Aconophora compressa Walker, a biological control agent released in 1995 to control Lantana camara (Verbenaceae) in Australia, has since been collected on several nontarget plant species. Our survey suggests that sustained populations of A. compressa are found only on the introduced nontarget ornamental Citharexylum spinosum (Verbenaceae) and the target weed L. camara. It is found on other nontarget plant species only when populations on C. spinosum and L. camara are high, suggesting that the presence of populations on nontarget species may be a spill-over effect. Some of the incidence and abundance on nontarget plants could have been anticipated from host specificity studies done on this agent before release, whereas others could not. This raises important issues about predicting risks posed by weed biological control agents and the need for long-term postintroduction monitoring on nontarget species.

Development of cat's claw creeper leaf-tying moth Hypocosmia pyrochroma (Lepidoptera: Pyralidae) at different temperatures: Implications for establishment as a biological control agent in Australia and South Africa

The leaf-tying moth Hypocosmia pyrochroma Jones (Lepidoptera: Pyralidae), a native of sub tropical South America, has been introduced as a biological control agent for cat’s claw creeper, Dolichandra unguis-cati (L.) Lohman (Bignoniaceae), in Australia and South Africa. So far there has been no evidence of its field establishment in either country. A narrow temperature tolerance is a potential limiting factor for the establishment of weed biological control insects in novel habitats. In this study, we evaluated the effect of seven constant temperatures (12–40 °C) on the survival and development of H. pyrochroma in temperature-controlled cabinets. Temperatures between 20 and 30 °C were the most favorable for adult survival, oviposition, egg hatching, and larval and pupal development. Adult survival (12–40 °C) and egg development (15–35 °C) showed tolerance for wider temperature ranges than oviposition, and larval and pupal development, which were all negatively affected by both high (>30 °C) and low (<20 °C) temperatures. The degree-day (DD) requirement to complete a generation was estimated as 877 above a threshold temperature of 12 °C. Based on DD requirements and an obligatory winter diapause of pupae from mid-autumn to mid-spring, the potential number of generations (egg to adult) the leaf-tying moth can complete in a year in Australia or South Africa range from one to three. A climate-matching model predicted that the inland regions of both Australia and South Africa are less favorable for H. pyrochroma than the coastal areas. The study suggested that H. pyrochroma is more likely to establish in the coastal areas of Australia where most of the cat’s claw creeper infestations occur, than in South Africa where most of the cat’s claw creeper infestations are inland.

Development of cat’s claw creeper leaf-tying moth Hypocosmia pyrochroma (Lepidoptera: Pyralidae) at different temperatures: Implications for establishment as a biological control agent in Australia and South Africa

The leaf-tying moth Hypocosmia pyrochroma Jones (Lepidoptera: Pyralidae), a native of sub tropical South America, has been introduced as a biological control agent for cat’s claw creeper, Dolichandra unguis-cati (L.) Lohman (Bignoniaceae), in Australia and South Africa. So far there has been no evidence of its field establishment in either country. A narrow temperature tolerance is a potential limiting factor for the establishment of weed biological control insects in novel habitats. In this study, we evaluated the effect of seven constant temperatures (12–40 °C) on the survival and development of H. pyrochroma in temperature-controlled cabinets. Temperatures between 20 and 30 °C were the most favorable for adult survival, oviposition, egg hatching, and larval and pupal development. Adult survival (12–40 °C) and egg development (15–35 °C) showed tolerance for wider temperature ranges than oviposition, and larval and pupal development, which were all negatively affected by both high (>30 °C) and low (<20 °C) temperatures. The degree-day (DD) requirement to complete a generation was estimated as 877 above a threshold temperature of 12 °C. Based on DD requirements and an obligatory winter diapause of pupae from mid-autumn to mid-spring, the potential number of generations (egg to adult) the leaf-tying moth can complete in a year in Australia or South Africa range from one to three. A climate-matching model predicted that the inland regions of both Australia and South Africa are less favorable for H. pyrochroma than the coastal areas. The study suggested that H. pyrochroma is more likely to establish in the coastal areas of Australia where most of the cat’s claw creeper infestations occur, than in South Africa where most of the cat’s claw creeper infestations are inland.

Australia's newest quarantine for biological control

The paper describes the QC3 quarantine facility and supporting infrastructure which were purpose built for weed biological control at the Ecosciences Precinct. The quarantine is one of two new weed quarantine facilities in Australia and will service northern Australia. An account of the sharing philosophy between CSIRO and the Queensland Government and the necessity of working very closely with architects, project managers, builders and quarantine personnel is also given. This philosophy contributed to certification of the facility without any undue delays.

Australia’s present scientific capacity to progress the biological control of weeds

Australia has a very proud record of achievement in biological control of weeds and the underpinning science. From the earliest campaigns against prickly pear and lantana, weed biocontrol developed with major contributions from CSIRO and state governments to produce outstanding successes against weeds such as salvinia, rubber vine, Noogoora burr, bridal creeper and prickly pear. Maximum research activity occurred in the 1980s when some 30 scientists were working world wide on Australia’s weed problems. Activity declined gradually until the last few years when government divestment in agricultural research greatly diminished capacity. There are now approximately eight full-time scientist equivalents supporting Australia’s weed biocontrol effort. Australia may now need to adopt a team approach to tackle future major weed biological control projects.

Use of CLIMEX modelling to identify prospective areas for exploration to find new biological control agents for prickly acacia

Selection of biocontrol agents that are adapted to the climates in areas of intended release demands a thorough analysis of the climates of the source and release sites. We present a case study that demonstrates how use of the CLIMEX software can improve decision making in relation to the identification of prospective areas for exploration for agents to control the woody weed, prickly acacia Acacia nilotica ssp. indica in the arid areas of north Queensland.