Target For Biological Control Research Articles

Biology and host specificity of the stem-boring weevil Gasteroclisus tricostalis, a candidate agent for the biological control of fireweed (Senecio madagascariensis) in Australia

ABSTRACT Senecio madagascariensis Poiret (Asteraceae) is a target for biological control in Australia, due to substantial impacts on agriculture and native environments. Studies in the plant’s native range in South Africa prioritised the stem-boring weevil Gasteroclisus tricostalis (Thunberg) (Curculionidae) as a candidate agent. In this study, we assessed the biology and host specificity of G. tricostalis during laboratory trials conducted in both South Africa and Australia. No-choice trials in South Africa revealed that, despite oviposition on 15 non-target Senecio species (seven Australian and eight South African), there was significantly lower oviposition relative to S. madagascariensis, with no survival to pupation or adulthood on any non-target species. In contrast, no-choice tests in quarantine in Australia, recorded oviposition on 12 non-target Australian native Senecio species, with oviposition on two species not significantly different to that on S. madagascariensis. Furthermore in Australia, larvae developed to adulthood on five non-target species, in numbers that were not significantly different to S. madagascariensis. These discrepancies can mostly be explained by the lower phylogenetic distance from S. madagascariensis to the susceptible non-target species tested in Australia and, likely, optimal plant growth conditions in quarantine in two cases. Although no-choice tests are renowned for their conservative nature, preliminary paired-choice trials in both South Africa and Australia failed to demonstrate clear oviposition preferences for S. madagascariensis. These results suggest that, given the high diversity of the genus Senecio in Australia, the weevil is likely unsuitable for release and further trials were suspended.

Prioritizing weeds for biological control development in the western USA: Results from the adaptation of the biological control target selection system

Nonnative invasive plants (weeds) negatively impact native ecosystems, and their effects are likely to increase with continuing global trade. Biological weed control has been employed as a cost-effective and sustainable management option for weeds in the USA since 1902. Biological control programs require careful prioritization of target weeds to ensure the most appropriate targets are selected to obtain the greatest beneficial outcomes with available resources. The Biological Control Target Selection (BCTS) system was developed by researchers in South Africa as an objective, transparent approach to prioritizing new weed biological control targets. The BCTS system was recently modified and applied to 295 state-regulated weeds in the western USA for which no biological control agents have yet been released. This paper presents the results of that application, identifying the most suitable candidates for new biological control programs as well as problematic weeds for which the likelihood of successful biological control is low.Top-ranked species in the western USA are biennial or perennial weeds that occur in stable habitats, are established in more than one state, have traits deemed difficult to control with conventional methods, have large negative impacts and no conflicts of interest outside of the horticultural industry, and have substantial information available on potential biocontrol agents. Fifteen of the 20 top-ranked species are already targets of ongoing biological control programs in the USA. When species with current programs are excluded from the analysis, the next 20 top-ranked species largely differ by having less information available on potential biological control agents and having native or economically important congeners in the USA. Results from this framework provide valuable insights to the prioritization of current and future biocontrol research programs in the western USA.

The benefits and potential of pre-emptive weed biological control: Three case studies in Queensland, Australia

Invasive weed species can have significant impacts on agriculture, biodiversity and livelihoods. The cost and feasibility of managing these species using conventional means can be prohibitive depending on the size of the infestations or the habitats in which they invade. Under these conditions, biological control is seen as a viable, sustainable means to manage many weeds. However, biological control can take many years and at considerable cost to achieve the desired level of control, due to the numerous steps that are involved, including native range surveys and host-specificity testing of potential agents. Pre-emptive biological control targeting particularly high-risk species prior to their arrival in a country or emerging weeds can be cost-effective, especially if the respective biological control agents have been utilized in other countries. While pre-emptive biological control of arthropods has been investigated previously, there are few examples of pre-emptive biological control of weed species. The invasive weed species, Chromolaena odorata, Mikania micrantha and Coccinia grandis have all been or are currently targets of pre-emptive biological control in Australia. Research on the gall fly Cecidochares connexa was initiated prior to its host, C. odorata being detected in Australia. Cecidochares connexa was eventually released in Australia to control C. odorata, after initial research on the agent found it to be suitably host specific and effective against the target weed. Cecidochares connexa has also been released in numerous other countries in Africa, Asia and the Pacific, where it is providing very good control. Australia funded research on the rust Puccinia spegazzinii as part of a project involving Fiji and Papua New Guinea while the target weed, M. micrantha was a target for eradication in Queensland. The rust was later approved for release in Australia to control M. micrantha following additional host-specificity testing. However, research funded by Australia overseas suggests that the rust may not be able to suppress M. micrantha populations below current levels. Consequently, while P. spegazzinii has been released in numerous countries now, it has not yet been field released in Australia. Biological control research in Australia on C. grandis is relatively new as the weed is relatively minor and not yet declared a target for biological control. Consequently, no biological control agents have yet been released in the country. Pre-emptive biological control of C. odorata and M. micrantha has been particularly cost-effective, not just for Australia, but subsequently for numerous other countries where these weeds were well-established and problematic and the respective biological control agents were later released.

Life cycle, host specificity and potential impact of a gall-inducing thrips Acaciothrips ebneri, a biological control agent for prickly acacia (Vachellia nilotica subsp. indica) in Australia

Prickly acacia (Vachellia nilotica subsp. indica (Benth.) Kyal. & Boatwr.; Fabales: Fabaceae) is a Weed of National Significance and a target for biological control in Australia. Currently there are no effective biological control agents for the weed in Australia. Based on genetic and climate matching, a gall thrips (Acaciothrips ebneri Karny; Thysanoptera: Phlaeothripidae) inducing rosette galls resulting in shoot tip dieback, was identified as a prospective biological control agent from Ethiopia. No-choice host-specificity tests were conducted on 59 test plant species in a high security quarantine in Brisbane, Australia. Acaciothrips ebneri is host-specific, inducing galls and reproducing only on prickly acacia. Acaciothrips ebneri, as predicted by the CLIMEX model, is suited to hot and arid western Queensland where major prickly acacia infestations occur. The Australian Government approved A. ebneri for field release in October 2022. This is the first time a true gall-inducing thrips has ever been approved as a weed biological control agent. Field releases commenced in January 2023 and are in progress. There are early signs of field establishment resulting in shoot tip die back in the field, and field release and monitoring will continue.

Pathogens of the oak processionary moth Thaumetopoea processionea: Developing a user-friendly bioassay system and metagenome analyses for microorganisms

The oak processionary moth (OPM) Thaumetopoea processionea is a pest of oak trees and poses health risks to humans due to the urticating setae of later instar larvae. For this reason, it is difficult to rear OPM under laboratory conditions, carry out bioassays or examine larvae for pathogens. Biological control targets the early larval instars and is based primarily on commercial preparations of Bacillus thuringiensis ssp. kurstaki (Btk). To test the entomopathogenic potential of other spore-forming bacteria, a user-friendly bioassay system was developed that (i) applies bacterial spore suspensions by oak bud dipping, (ii) targets first instar larvae through feeding exposure and (iii) takes into account their group-feeding behavior. A negligible mortality in the untreated control proved the functionality of the newly established bioassay system. Whereas the commercial Btk HD-1 strain was used as a bioassay standard and confirmed as being highly efficient, a Bacillus wiedmannii strain was ineffective in killing OPM larvae. Larvae, which died during the infection experiment, were further subjected to Nanopore sequencing for a metagenomic approach for entomopathogen detection. It further corroborated that B.wiedmannii was not able to infect and establish in OPM, but identified potential insect pathogenic species from the genera Serratia and Pseudomonas.

PROSPECTS FOR THE BIOLOGICAL CONTROL OF WEEDS IN ARGENTINA

Argentina hosted pioneering classical weed biological control projects that were carried out by state institutions between the 1970s and 1990s, at a time when the practice was almost unheard of in Latin America. Despite the early development of these initiatives, the discipline did not prosper and all projects were discontinued. Notwithstanding, Argentina continued to provide biological control agents for the control of weeds in many other parts of the world, ensuring the expertise persisted. Although public concern about invasive plants and chemical-dependent agricultural practices has increased over time, it did not lead to a greater acceptance of classical biological control of weeds, which is still regarded with mistrust or ignored in many public and academic circles alike. Furthermore, there are no systems in place to reach a consensus on declaring weeds as targets for biological control in Argentina. In this paper we discuss different ways in which the community of researchers working in the field in Argentina can help relaunch the biological control of weeds, including the preparation of a prioritized list of target species. A list of this kind would not only reduce costs, but also help in developing trust in the discipline of biological control informing regulators and decision makers in this regard. Prospects are brighter today than a few years ago, but considerable communication and educational work on the benefits of this practice is still required to gain more support before it can effectively be re-implemented.

Involvement of a catalase gene in lignin catalysis and immune defense against pathogenic fungus in Coptotermes formosanus: a potential new target for termite control.

Detoxifying enzymes are likely involved in lignin feeding and immune defense mechanisms within termites, rendering them potential targets for biological control. However, investigations into the dual functionality of termite detoxification enzymes in vivo have not been documented. In this study, the complete cDNA of the catalase gene (Cfcat) derived from Coptotermes formosanus Shiraki was amplified. CFCAT comprises an open reading frame spanning 1527 bp, encoding a 508-amino acid sequence. The highest expression was observed in the epidermal tissues (including the fat body and hemolymph) followed by the foregut/salivary gland. Furthermore, we confirmed the catalase activity of the recombinant Cfcat protein. Using RNA interference (RNAi) technology, the importance of Cfcat in the lignin-feeding of C. formosanus was demonstrated, and the role of Cfcat in innate immunity was investigated. Survival assays showed that Cfcat RNAi significantly increased the susceptibility of C. formosanus to Metarhizium anisopliae. Irrespective of the infection status, Cfcat inhibition had a significant impact on multiple factors of humoral and intestinal immunity in C. formosanus. Notably, Cfcat RNAi exhibited a more pronounced immunosuppressive effect on humoral immunity than on intestinal immunity. Cfcat plays an important role in the regulation of innate immunity and lignin feeding in C. formosanus. Cfcat RNAi can weaken the immune response of termites against M. anisopliae, which may aid the biocontrol efficiency of M. anisopliae against C. formosanus. This study provides a theoretical basis and technical reference for the development of a novel biocontrol strategy targeting detoxifying enzymes of termites. © 2024 Society of Chemical Industry.

Will climate affect the establishment and efficacy of Agnippe sp. #1 (Lepidoptera: Gelechiidae), a promising biological control agent of Mesquite in South Africa?

Several spiny leguminous tree species within the genus Neltuma Raf. (formerly Prosopis L.) (Fabaceae) occur as widespread invasive alien plants in South Africa, exerting severe negative socio-economic and ecological impacts. Given these impacts, South Africa recently released the leaf-tying moth Agnippe sp. #1 (syn. Evippe sp. #1) (Lepidoptera: Gelechiidae) as a biological control agent against invasive Neltuma species in 2021. The widespread invasion of Neltuma spp. across a vast and climatically diverse range of South Africa has led to concerns regarding the establishment and impact of the agent. Therefore, this study aimed to assess the constraints posed by climate to the potential establishment and efficacy of Agnippe sp. #1 using both climatic matching (CLIMEX) and thermal-physiology assessments. Climatic analyses revealed relatively high (71%) and moderate (66%) matches of South Africa to the native (Argentina) and introduced (Australia) ranges of Agnippe sp. #1 respectively. Thermal assessments of Agnippe sp. #1, particularly the 4th instar larvae, determined a CTmin = 0.9 ± 0.3 °C and LLT50 = −11.1 ± 0.4 °C, which suggest the moth is suited mainly to warmer regions of South Africa. Overall, these assessments propose that the establishment and performance of Agnippe sp. #1 is likely to be constrained by climate in parts of South Africa, particularly within the cold semi-arid and temperate provinces of the country. Promisingly, these climatic comparisons suggest that Agnippe sp. #1 may become more widely established in the hottest parts of the Northern Cape province, which remains a major biological control target region for Mesquite in South Africa.

Anthropogenic disturbance affects specialist, but not generalist, endophagous insects associated with two African grasses: implications for biological control

ABSTRACT The specialisation-disturbance hypothesis (SDH) predicts that specialist and generalist taxa respond differently to disturbance, with generalists more tolerant of disturbance, while habitat stability (i.e. no/limited disturbance) should favour specialist species. If the SDH holds true, this would have implications for the design and implementation of biological control programmes, in terms of performing native-range surveys in search of candidate agents and subsequent development of management programmes for their release in the weeds invaded range. We assessed the effect of anthropogenic disturbance (mowing/slashing and fire) on the endophagous insect communities associated with two African grasses, Sporobolus pyramidalis and Sporobolus natalensis (Poaceae), that are targets for biological control in Australia. Comparisons, of insect community structure and presence/abundance of each species between disturbed and undisturbed sites, were made at 19 sites in South Africa. Disturbance caused a shift in insect species composition and abundance, whereby specialist insects were less frequently encountered and less abundant at disturbed versus undisturbed sites. If the potential agents for Sporobolus spp. are released in Australia they may be negatively affected by disturbance and may therefore be incompatible with certain integrated management strategies, such as mowing and prescribed burning. Moreover, our results suggest that field sites with limited disturbance should be prioritised during native-range surveys to maximise the chances of locating specialist natural enemies. The effect disturbance has on insect community composition may be particularly relevant for the biological control of invasive grasses, due to the intensity of disturbance of grasslands worldwide.

Interactions between Phaedrotoma scabriventris Nixon (Hymenoptera: Braconidae) and Zaeucoila unicarinata Ashmead (Hymenoptera: Figitidae), endoparasitoids of Liriomyza sativae Blanchard (Diptera: Agromyzidae)

Liriomyza sativae Blanchard is a key pest of melon (Cucumis melo L.) in Brazil and a target of biological control using parasitoids. Even though they share similar niches and competitive interactions can occur, Phaedrotoma scabriventris Nixon and Zaeucoila unicarinata Ashmead are potential candidates for controlling L. sativae in melon. Here, we investigated interactions between P. scabriventris (Ps) and Z. unicarinata (Zu) under laboratory conditions. We evaluated: (1) puparia to verify both parasitism and the interactions between parasitoid immature stages; and (2) emerged adults to verify host mortality due to parasitism, host stinging, host feeding, and parasitoid sex ratios. We observed in the dissected puparia that P. scabriventris predominated in all three forms of interaction evaluated. In addition, predation and physical combats were observed between immature stages of both parasitoids. When we consider the emerged adults, both species showed a similar parasitism rate in isolation (P. scabriventris, 19.40 ± 3.57 % and Z. unicarinata, 17.60 ± 4.54 %). The sequential interaction (Zu → Ps) significantly decreased the parasitism by Z. unicarinata (4.92 ± 0.14 %) compared to its parasitism rate in isolation. The greatest total parasitism rate was observed when both species simultaneously (Ps + Zu) parasitised the larvae (51.28 ± 3.08 %). Phaedrotoma scabriventris and Z. unicarinata caused the greatest non-reproductive larvae mortality under the isolated exposure forms (35.90 ± 2.55 % and 37.00 ± 4.60 %, respectively). The sex ratio decreased significantly only in P. scabriventris (22.62 % of females) in the sequential interaction (Ps → Zu). Our results indicate that both P. scabriventris and Z. unicarinata should be used in combination in the control of L. sativae in melon.

Prioritization of alien plant targets for biological control in South Africa's offshore sub-Antarctic islands

AbstractInvasive alien plants (IAPs) are a significant threat to the biodiversity and ecological functioning of the sub-Antarctic Prince Edward Islands (PEIs); however, weed biological control has not yet been implemented as a management tool. The PEIs have had 23 alien plants recorded, of which several are considered beyond eradication and therefore could benefit from the release of safe and effective biocontrol agents. We used the South African Biological Control Target Selection (BCTS) system to provide a ranked list of the target species in order of priority for further biocontrol research. The highest-scoring species, and therefore those that should be considered first to be targeted, were Sagina procumbens and Cerastium fontanum. No biocontrol agents for IAPs have been released in any climate with as consistent low temperatures as in the PEIs, so the climatic compatibility of agents will be essential prior to any decision to release. However, with very few native species present on the PEIs, the programmes would involve limited host specificity testing, which would improve the feasibility and speed with which new biocontrol agents could be developed. Biocontrol may offer an environmentally safe and sustainable method of reducing the negative impacts of these priority species and thus warrants further investigation.

Contrasting effects of climate change on the invasion risk and biocontrol potential of the invasive Iris pseudacorus L. between Northern and Southern Hemisphere

Iris pseudacorus is both a prized ornamental and an invasive aquatic plant that tends to grow dense monospecific stands, displacing the local vegetation and altering the hydrology of freshwater ecosystems. Originally from Europe, this species has historically invaded North America, China and Japan, and more recently spread through Argentina, South Africa and Australasia, where it is now a target for biological control. Field surveys within its native range have led to the selection of three candidate biocontrol agents. Prioritizing the best candidates for different regions constitutes a critical step, which could save significant time and resources before further cost-intensive experimental studies are conducted. Climate change is seldom taken into consideration in the prioritization process. In this regard, climatic suitability can be used to model the potential distributions of weeds and their candidate agents, both in space and time, thus allowing to identify areas at risk of invasion and predict where agents will be able to establish long-term. Accordingly, the objectives of this work were (i) to predict I. pseudacorus invasions and range shifts in the context of climate change; (ii) to identify wetland areas most at risk of invasion under present and future climatic conditions; and (iii) to prioritize the best suite of candidate biocontrol agents for different invaded ranges, worldwide. To do so, we modelled the present and future (2040–2060) climatic suitability of I. pseudacorus and its candidate agents using the software MaxEnt. Our results highlight a clear distinction between predictions for the Northern and Southern Hemispheres. In North America and eastern Asia, the area climatically suitable for I. pseudacorus is expected to increase and shift northwards. As for its biocontrol agents, very low suitability is predicted across these regions, further decreasing under future climatic conditions. On the other hand, climatically suitable areas for the plant in South America, southern Africa and Australasia are predicted, on average, to reduce in response to climate change. A decrease in climatic suitability is also expected for its candidate biocontrol agents which, however, would still maintain a significant range overlap with their host. These results can be used to prioritize areas most at risk of invasion and identify which combination of candidates could potentially provide the best level of control across different invaded ranges.

Effects of elevated CO2 on feeding responses of biological control agents of Pontederia crassipes

AbstractElevated carbon dioxide (eCO2) and rising temperatures will have far‐reaching effects on global plant‐insect interactions, yet their implications for future biological control programs are not fully understood. Studies have shown that elevated CO2 will affect insect feeding guilds differently and these responses can be predicted with some confidence. Water hyacinth, Pontederia crassipes Mart. (Pontederiaceae), is a native and representative species of the Del Plata wetlands (Argentina) that invades outside of its native environment. It is considered one of the world's worst aquatic weeds and a target for biological control. In this study, water hyacinth plants were grown under two CO2 concentrations – current (400 p.p.m.) or elevated (800 p.p.m.) –, with and without two biocontrol agents representing different feeding guilds, the leaf‐chewing Cornops aquaticum Brüner (Orthoptera: Acrididae) and the phloem‐feeding Megamelus scutellaris Berg (Hemiptera: Delphacidae). Under eCO2 concentration, photosynthetic rate, total dry weight, and relative growth rate of P. crassipes acclimated to eCO2 conditions and plants showed very little CO2 fertilization response in eutrophic water. Insect herbivory varied depending on feeding guilds at eCO2; however, P. crassipes growth responses increased when exposed to insect herbivory. Chewing herbivory by C. aquaticum was consistent across CO2 conditions, whereas the feeding by M. scutellaris increased substantially at eCO2. These results indicate that successful biological control of P. crassipes under conditions of elevated CO2 might rely on phloem‐feeding insects, with chewers playing a lesser role.

Host-plant affinities of stem-boring weevils and moths associated with fireweed (Senecio madagascariensis) in South Africa: evaluating native host ranges of candidate biocontrol agents using DNA barcoding

ABSTRACT Native to South Africa and Madagascar, the invasive fireweed, Senecio madagascariensis Poiret (Asteraceae), is a target for biological control in Australia and Hawaii, where substantial infestations persist. Earlier studies in the weed’s region of origin, namely KwaZulu-Natal Province in South Africa, assessed the seasonal abundance of stem-boring insect herbivores in S. madagascariensis populations. The weevil Gasteroclisus tricostalis (Thunberg) (Curculionidae) and moth Metamesia elegans (Walsingham) (Tortricidae) were prioritised as candidate agents for Australia due to their persistence across seasons. In this study, the host ranges of these two candidate agents were assessed by comparing the stem-boring curculionids and lepidopterans that are associated with S. madagascariensis with those associated with non-target Senecio species in the KwaZulu-Natal Midlands region. DNA barcoding of the adults and endophagous larvae recovered during field sampling of S. madagascariensis and 17 non-target Senecio species in 2017/18, as well as those from earlier field surveys, was used to differentiate the insect species and elucidate their host-plant affinities. Although weevil larvae were recovered from the stems of seven non-target Senecio species, G. tricostalis was associated only with Senecio inaequidens DC. and Senecio skirrhodon DC., both in the S. madagascariensis species complex. Lepidopteran larvae were associated with three non-target Senecio species, all in the S. madagascariensis species complex, with M. elegans associated only with Senecio harveianus MacOwan and S. inaequidens. These results suggest that G. tricostalis and M. elegans have restricted host ranges and that further host-specificity studies in quarantine are warranted to demonstrate their suitability for release.

Seasonal abundance of capitulum-boring insects considered for the biological control of fireweed (Senecio madagascariensis), including molecular phylogenetic analyses to reveal the field host range of lepidopteran candidate agents

Senecio madagascariensis Poiret (Asteraceae; fireweed) is a target for biological control in Australia and Hawaii, due to its severe impacts on agriculture and grazed rangelands. Prioritized candidate biocontrol agents recorded in KwaZulu-Natal Province, South Africa (accepted as the plant’s region of origin) include capitulum-boring Lepidoptera. The seasonal abundance of capitulum-boring insects was studied on S. madagascariensis populations in KwaZulu-Natal during 2017/18. The host-plant affinities of lepidopteran associates were subsequently assessed by surveying 34 non-target native Senecio species in the same region. Cytochrome c oxidase subunit 1 mitochondrial gene barcoding was used to differentiate the endophagous larvae associated with the various host plants and link them with their adult stages. Monthly sampling revealed low numbers of capitulum-boring insects in relation to available capitula, with no significant variation amongst sites or months. Larvae largely comprised Coleoptera (72.8%), with fewer Lepidoptera (15.8%) and Diptera (11.4%). Adults reared from the capitula comprised Coleoptera (Nitidulidae), Diptera (Agromyzidae, Cecidomyiidae, Tephritidae) and Lepidoptera (Pterophoridae, Pyralidae). The host-range study revealed 14 lepidopteran taxa on 13 Senecio species, with Homoeosoma stenotea Hampson (Pyralidae) and an unidentified species of Platyptilia Hübner (Pterophoridae) comprising the most abundant species and recorded mostly on S. madagascariensis. However, H. stenotea was recorded on six, and Platyptilia sp. on two, non-target Senecio species. These results suggest unacceptably broad host ranges for countries like Australia that host a diverse Senecio flora and require highly specific biocontrol agents. Both species may warrant further investigation in Hawaii, where there are no native Senecio species.

Suppression of yolk formation, oviposition and egg quality of locust (Locusta migratoria manilensis) infected by Paranosema locustae.

Locusta migratoria manilensis is one of the most important agricultural pests in China. The locust has high fecundity and consumes large quantities of food, causing severe damage to diverse crops such as corn, sorghum, and rice. Immunity against pathogens and reproductive success are two important components of individual fitness, and many insects have a trade-off between reproduction and immunity when resources are limited, which may be an important target for pest control. In this study, adult females L. migratoria manilensis were treated with different concentrations (5 × 106 spores/mL or 2 × 107 spores/mL) of the entomopathogenic fungus Paranosema locustae. Effects of input to immunity on reproduction were studied by measuring feeding amount, enzyme activity, vitellogenin (Vg) and vitellogenin receptor (VgR) production, ovary development, and oviposition amount. When infected by P. locustae, feeding rate and phenol oxidase and lysozyme activities increased, mRNA expression of Vg and VgR genes decreased, and yolk deposition was blocked. Weight of ovaries decreased, with significant decreases in egg, length and weight.Thus, locusts used nutritive input required for reproduction to resist invasion by microsporidia. This leads to a decrease in expression of Vg and VgR genes inhibited ovarian development, and greatly decreased total fecundity. P. locustae at 2 × 107 spores/mL had a more obvious inhibitory effect on the ovarian development in migratory locusts. This study provides a detailed trade-off between reproduction and immune input of the female, which provides a reliable basis to find pest targets for biological control from those trade-off processes.

Prioritisation of damaging weed biological control agents for prickly acacia (Vachellia nilotica subsp. indica) based on insect exclusion studies in the native range

Prickly acacia, Vachellia nilotica subsp. indica (Benth.) Kyal. & Boatwr. (Fabaceae), native to India, is a target for biological control in Australia. Native range insecticide exclusion studies were conducted at two sites (Coimbatore and Thoppur) in India to evaluate the impact of insect herbivores on prickly acacia, to prioritise agents. At each site, prickly acacia plants were either exposed to or protected from insect herbivores and the incidence of insects were recorded at quarterly intervals. More insect species occurred at Thoppur (12) than at Coimbatore (9) and among them the scale insect Anomalococcus indicus Ayyar (Hemiptera: Lecanodiaspididae) was the predominant species at both sites. Insect herbivory significantly reduced plant height, basal stem diameter, number of branches, the number of leaves, and stem biomass at Coimbatore, while the impact was evident only for plant height at Thoppur. However, there were significant reductions in plant height (38–55%), basal stem diameter (20–31%), number of branches (21–45%), number of leaves (79–99%), leaf biomass (81–96%), stem biomass (67–84%) and root biomass (61–84%) in plants infested with A. indicus than in plants without A. indicus in insects excluded plots. Infestation by A. indicus resulted in 18 and 27% plant mortality in Coimbatore and Thoppur, respectively. Based on potential impact, A. indicus was prioritised for importation and detailed host-specificity testing in Australia.

MicroRNAs shape social immunity: a potential target for biological control of the termite Reticulitermes chinensis

Eusocial insects can employ various behavioural and physiological disease defences to avoid, resist and tolerate pathogen infections in their closely related and packed colonies, termed social immunity. Recent studies have shown that several molecules serve insect social immunity, including chemical odours, insect venoms, immune-related proteins, etc. However, whether and how microRNAs (miRNAs), whose precursors are processed by Dicer-1, drive social immunity in insect colonies is still unknown. Here, we used a ‘host–pathogen’ system (host: Reticulitermes chinensis; pathogen: Metarhizium anisopliae) to explore the impact of miRNAs on social immunity in termite colonies. We found that RNAi-mediated silencing of Dicer-1 led to decreased miRNA concentration, significantly inhibited carbohydrate and energy metabolism and affected other life processes, such as the immune response and oxidation–reduction reactions, in whole body of the termite. In behavioural defence, silencing Dicer-1 significantly diminished defensive social behaviours such as locomotion, grooming, cannibalism and burial in termite groups when encountering fungal contamination. In physiological defence, Dicer-1 silencing and miR-71-5 stimulation resulted in significantly decreased antifungal activities of termites. Furthermore, both Dicer-1-silenced and miR-71-5 stimulant-treated termite groups exhibited a high level of mortality during fungal contamination. Our findings demonstrated the important role of miRNAs in shaping social immunity in termite colonies, providing insights necessary to understand the potential mechanisms underlying behavioural and physiological disease defences in insects and hence laying the groundwork for miRNA-based pest control.

Seasonal abundance of stem-boring insects associated with the invasive Senecio madagascariensis in its native range (KwaZulu-Natal, South Africa) and their potential for biological control

ABSTRACT Fireweed, Senecio madagascariensis Poiret (Asteraceae), is a target for biological control in Australia and Hawaii. Candidate agents recorded in KwaZulu-Natal Province, South Africa, the region of origin of the invasive populations, include stem-boring insects. The seasonal abundance of stem borers associated with S. madagascariensis populations was studied at four field sites in the KwaZulu-Natal Midlands region, during 2017/18. DNA barcoding was used to differentiate and link insect taxa with their endophagous larvae. Monthly sampling revealed that stem-boring larvae comprised largely Diptera (42% of specimens) and Curculionidae (38.9%), with Lepidoptera (19.8%) the least abundant. Differences in larval herbivore loads between sites were statistically significant, with the warmer and drier sites supporting 59% higher larval numbers. DNA barcoding focused on Curculionidae and Lepidoptera, which took precedence due to restricted host ranges. Of the four lineages of weevil larvae recorded, 95% of sequenced specimens comprised two maternal lineages of Gasteroclisus tricostalis (Thunberg). Collectively, G. tricostalis was detected across nine months of the year, with peaks in abundance in autumn and summer. Similarly, of the three lineages of lepidopteran larvae recorded, 83% of sequenced specimens comprised Metamesia elegans (Walsingham) (Tortricidae). Metamesia elegans was collected across six months of the year, with an autumn peak. These results support the prioritisation of G. tricostalis and M. elegans as the most promising stem-boring agents for S. madagascariensis. The higher seasonal abundance of G. tricostalis, together with the good track record of weevils in weed biocontrol, suggest that it should take precedence in subsequent laboratory host-range assessments.

Recent Advances in the Biological Control of Tecoma stans L. (Bignoniaceae) in South Africa

Tecoma stans (L.) Juss ex Kunth var. stans (Bignoniaceae) is an invasive shrub or small tree from Central America that continues to extend its range in all nine provinces of South Africa and in neighbouring countries. The weed has been a target for biological control (biocontrol) in South Africa since 2003. The gall-forming rust fungus Prospodium transformans (Ellis & Everh.) Cummins (Pucciniales: Uropyxidaceae) was released in 2010, but failed to establish. Two leaf-feeding agents, Mada polluta (Mulsant) (Coleoptera: Coccinellidae) and Pseudonapomyza sp. Hendel (Diptera: Agromyzidae), were subsequently released in South Africa in 2013 and 2014, respectively. Mada polluta has become established at seven sites in the low elevation coastal regions of the Eastern Cape and KwaZulu-Natal provinces, but not in high elevation inland areas. The leaf-mining Pseudonapomyza sp. has established at seven sites in four provinces, namely the Eastern Cape, KwaZulu-Natal, Limpopo and Mpumalanga, but at low population densities. The deliberate destruction of release sites by landowners and inadvertent veld fires have confounded the establishment and proliferation of both agents, as well as progress on their post-release evaluation. A root-feeding flea beetle Heikertingerella sp. Csiki (Chrysomelidae: Galerucinae), initially collected in Mexico in 2007, was determined to be host specific and potentially effective as a new biocontrol agent of T. stans. An application for the release of Heikertingerella sp. in South Africa will shortly be submitted to the regulatory authorities. Additional mass-rearing and releases of the two established agents will be undertaken to improve their establishment and impact.