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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. [ABSTRACT FROM AUTHOR]

Delairea odorata Lemaire, Cape ivy (Asteraceae: Senecioneae), is native to South Africa but invasive in several countries. The plant is a target for biological control in the USA (California and Hawaii) and Australia, where its aggressive smothering tendencies threaten native ecosystems. The beetle Ageniosa cf. badenii (Vogel) (Chrysomelidae) was investigated in South Africa as a potential agent for D. odorata in invaded countries. Adults are wingless and nocturnal. Females deposit clusters of 1–10 eggs on the leaf undersides. Neonate larvae are highly mobile and feed on the leaves during the four instars, before pupating in the soil. Mean (± SE) developmental time from egg hatch to adult emergence was 30.8 ± 0.4 days on D. odorata. During larval no-choice tests with 34 asteraceous plant species, survival to adulthood was confined to 10 species in the tribe Senecioneae. Neonate larvae completed development (with sustained fitness ≥ 65% in relation to the highest ranked host) on three native (Senecio tamoides DC., D. odorata and S. skirrhodon DC.) and one exotic (Gynura procumbens (Lour.) Merr.) species. The beetle's narrow host range was confirmed by larval paired-choice and adult multi-choice tests and field observations. Ageniosa cf. badenii may be a suitable agent for Hawaii, where the tribe Senecioneae is not represented in the native flora. However, since Senecioneae are well represented in the native flora of Australia and California, more intensive testing is needed to determine if the beetle is a candidate for introduction into these areas. [ABSTRACT FROM AUTHOR]

Native to southern Africa, Senecio madagascariensis Poir. (fireweed, Asteraceae) has invaded agricultural lands and disturbed areas in several countries worldwide and is currently a target for biological control in Australia and the USA (Hawaii). Quantitative surveys of the plant in KwaZulu-Natal, South Africa, considered the origin of the Australian and Hawaiian populations, revealed several insect herbivore taxa that are frequently associated with the plant's foliar, floral and structural tissues. These largely comprised ectophagous sap suckers (34%), chewers (29%) and root feeders (1%), but also endophagous stem borers (21%), capitulum feeders (13%) and leaf miners (2%). Many of these taxa were encountered only occasionally or rarely during sampling, with some displaying low to very low abundance. Based on these surveys and earlier precedents in biocontrol programmes against other invasive Asteraceae, 15 taxa were shortlisted as candidate agents. Of these, four were prioritised for host-range assessments which are currently in progress. These include the capitulum-feeding Homoeosoma stenotea Hampson (Lepidoptera: Pyralidae), the stem-boring Gasteroclisus tricostalis (Thunberg) (Coleoptera: Curculionidae) and Metamesia elegans (Walsingham) (Lepidoptera: Tortricidae) and the root-feeding Longitarsus basutoensis Bechyné (Coleoptera: Chrysomelidae: Alticinae). Although the diversity of native Senecio species in Australia may present challenges during routine host-specificity testing, prospects for the biocontrol of S. madagascariensis in Hawaii appear very promising, since the native flora does not include any species in the tribe Senecioneae. [ABSTRACT FROM AUTHOR]

• DNA barcoding revealed host-plant affinities in endophagous fireweed insects. • Capitulum-feeding flies and stem-boring weevils and moths had narrow host ranges. • Stem-boring flies utilized host plants outside the fireweed species complex. • Native-range surveys and COI phylogenies facilitated fireweed agent selection. Senecio madagascariensis Poiret (Asteraceae), an invasive herb from southern Africa that inflicts high economic losses in several countries worldwide, is currently a target for biological control in Australia and Hawaii. Several candidate insect agents were identified from the weed's native range in South Africa. Confirmation of narrow host ranges, prior to agent importations into quarantine, is important for Australia given its rich native Senecio flora. In particular, surveys for candidate agents on closely related non-target plants in the native range can differentiate between host specific and unsuitable agents at an early stage. This study focused on endophagous insects from families that were deployed in biocontrol programmes against other weedy Asteraceae. The host-plant affinities of stem-boring Coleoptera and stem-boring and capitulum-feeding Lepidoptera and Diptera were assessed across 18 native herbaceous Senecio species in KwaZulu-Natal, South Africa. Since larval morphology is typically unable to confirm insect identity, DNA barcoding was used to differentiate between insect species associated with different Senecio species to determine their host-plant affinities. COI phylogenies revealed that stem-boring Curculionidae and Tortricidae and capitulum-feeding Pterophoridae and Tephritidae that are associated with S. madagascariensis were restricted to plants in the S. madagascariensis species complex. In contrast, none of the stem-boring Agromyzidae were restricted to S. madagascariensis or its species complex. This study has supported the selection of several potentially host-specific agents for S. madagascariensis that could be imported for quarantine testing in Australia and Hawaii. [ABSTRACT FROM AUTHOR]

[Display omitted] • Stem-boring weevils are promising candidates for the biocontrol of fireweed. • Shoot production and flowering decreased with increasing larval densities. • Aggressive intraspecific interactions may increase larval mortality. • Reducing fireweed's high floral production may contribute to its control. The stem-boring weevil Gasteroclisus tricostalis (Thunberg) (Curculionidae) is under investigation as a biological control agent for Senecio madagascariensis Poiret (Asteraceae) in Australia and Hawaii. Besides mandatory host-specificity testing, pre-release studies on the weevil's impact can be a useful predictor of its efficacy when released in the invaded range. In this study, we investigated the response (i.e., growth, floral production, and biomass accumulation) of mature flowering S. madagascariensis plants to varying densities of G. tricostalis larvae in their stems. Although there were weak negative relationships between plant response variables and larval densities, these were only significant in the production of side branches (shoots) and floral components (capitula). Regression analyses estimated that six and 12 larvae per mature plant could prevent the production of new capitula and new shoots, respectively. A significant negative relationship between the percentage of eggs that resulted in larval recoveries and the number of eggs deposited per plant may suggest aggressive interactions between the larvae. Given precedents from other biocontrol programmes against asteraceous weeds, G. tricostalis may exhibit higher impacts on young pre-flowering plants than on mature plants, a possibility that requires confirmation. Because G. tricostalis is present is the field throughout most of the year, additional testing involving multiple generations of the weevil can assess the ultimate impact of sustained damage on plants. Since high floral production is a major driver of invasions by S. madagascariensis , substantial reductions in flowering by G. tricostalis would likely make a significant contribution to the weed's management. [ABSTRACT FROM AUTHOR]

[Display omitted] • Lepidoptera formed a small proportion of capitulum-boring larvae on fireweed. • DNA barcoding revealed the native host ranges of two capitulum-boring moths. • Homoeosoma stenotea utilized six non-target Senecio species in the field. • Platyptilia sp. was uncommon and recorded on two non-target Senecio species. • Both moths appear unsuitable for countries with a diverse Senecio flora. 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. [ABSTRACT FROM AUTHOR]

[Display omitted] • Native host ranges of flea beetles on fireweed were assessed by DNA barcoding. • Longitarsus basutoensis was abundant but limited by site rather than season. • Field surveys detected L. basutoensis on four non-target Senecio species. • Six non-target plant species were utilized as hosts in multi-choice tests. • This flea beetle is unsuitable for countries with a diverse Senecio flora. Senecio madagascariensis Poiret (Asteraceae) is a target for biological control in Australia and Hawaii, with several candidate insect agents recorded in KwaZulu-Natal, South Africa, the confirmed origin of the invasive populations. Although the root-feeding Longitarsus basutoensis Bechyné (Chrysomelidae: Galerucinae: Alticini) was prioritised for assessment, similar flea beetle taxa were also considered. We first investigated the seasonal abundance of L. basutoensis and related taxa on S. madagascariensis populations in the KwaZulu-Natal Midlands. Second, we assessed their host-plant affinities by surveying 17 non-target native Senecio species in the region. We used DNA CO1 barcoding to differentiate flea beetle taxa and their root-feeding larvae in both studies. Monthly sampling revealed three root-feeding taxa associated with S. madagascariensis , with L. basutoensis the most abundant. Longitarsus basutoensis was recorded throughout the year, with no clear patterns in seasonal abundance but significantly higher numbers at sites with deep, well drained soils that have high water holding capacity. Two unidentified flea beetle taxa, represented by larval specimens only, were recorded infrequently and in low numbers. The host-range study revealed 18 flea beetle taxa on 11 Senecio species, with L. basutoensis the most abundant species and recorded mostly on S. madagascariensis. Longitarsus basutoensis was also detected on four non-target Senecio species which, together with the results of preliminary host-specificity tests, indicated insufficient host-range restriction for countries like Australia that host a diverse Senecio flora. However, L basutoensis may have potential for release in Hawaii, due to a lack of native Senecio species on any of its islands. [ABSTRACT FROM AUTHOR]