No abstract

Tibraca limbativentris (Hemiptera: Pentatomidae) is a major pest in Neotropical rice agroecosystems. In autumn–winter, this pest takes refuge in rice stubble and in native vegetation, which allows it to re-colonize the crop during the rice growing season. However, it is still unknown whether this vegetation is a pest sink or is actually a natural trap that contributes to pest population biocontrol. Here we present information on the insect's alternative host plants, a preliminary outline of the relationship between plant phylogeny and insect abundance, and the impact that winter natural enemies have in pest population. Also, we include a proposed methodology for pest density analysis in winter hosts. Our results show significant differences in the abundance/density that T. limbativentris reaches in the 12 host plant species present in our study areas, with a plant-use pattern significantly related to the phylogenetic clade of Poales. Stink bug winter populations mainly comprised diapause adults, and 40% of insect digestive tracts had content. Survival of T. limbativentris was 56.92% in winter hosts. About mortality, 10% was due to undetermined causes and 33.08% due to entomopathogenic fungi, showing a natural regulation of the pest population. Our results suggest that native vegetation impacts winter survival of T. limbativentris. Although these plants offer shelter, they offer a greater contribution to Integrated Pest Management: the natural regulation of winter pest populations through entomopathogenic attack. Further studies on T. limbativentris population dynamics and the preservation of native areas near rice fields will be required for the development of best control practices.

Tibraca limbativentris is a major stink bug pest in paddies of the Neotropics. In Argentina, its populations overwinter in twelve host-plant species that occur inside rice fields. However, it's unknown if there are local scale variations in the abundance of T. limbativentris. Likewise, the role of host-plant community composition (H p CC) as a factor involved in the winter host-plant selection by the insects is poorly understood.The aims of this work were (a) to assess variations at local scale on the abundance of T. limbativentris in the context of winter H p CC and incidence of entomopathogenic fungi (EPFs) and (b) to assess the abundance of T. limbativentris considering the relationship between the height of plants of rice cultivars present in target sites during summer, and the height of the hosts selected by T. limbativentris during winter in grassland adjoining rice plots. Sampling was carried out during summer-winter in different commercial rice fields, to assess winter abundance of T. limbativentris, H p CC in grasslands adjacent to rice plots and incidence of EPFs. Height measurements of winter hosts and summer rice plants in target plots were taken. Our results show that H p CC differed at the local scale, with significant differences in stink bug abundance between winter hosts in each site. Also, we found differences in the action of EPFs species recorded on the insects and variations in plant height between host species.A positive correlation was obtained between the height of the different rice cultivars used during spring-summer in target sites and the height of the hosts selected by T. limbativentris near to these plots during winter. This shows that the height of the rice cultivar could be a factor related to the local selection of winter hosts by T. limbativentris. These results serve as a framework for future research, contributing to integrated pest management for target sites. K E Y W O R D S entomopathogenic fungi, integrated pest management, paddies, plant height, rice cultivars, stink bug pest | 323 FUENTES-RODRÍGUEZ ET al. S U PP O RTI N G I N FO R M ATI O N Additional supporting information may be found online in the Supporting Information section.

Host specificity determination of weed biocontrol agents has historically relied on evidence generated through quarantine trials in the region of introduction. These trials could give ‘false positive’ results due to a maximum type I error probability, and where possible, more research under field conditions should be conducted in the region of origin. The oligophagous, semiaquatic grasshopper, Cornops aquaticum Bruner (Orthoptera: Acrididae, Tetrataeniini), was released in South Africa for the biological control of Pontederia crassipes Pellegrini and Horn (Pontederiaceae). The aim of this study was to assess how the performance and field host range of C. aquaticum varies according to its stages of development, and how this contributes to the understanding of the relationship between the fundamental (laboratory‐based) and the ecological (field‐based) host range of this grasshopper, and its implications for water hyacinth biocontrol. We conducted post‐release laboratory no‐choice trials, confining early instars (instars 1 and 2), later instars (instars 3–6), and adult females and males in mesh cages, to determine insect performance on wetland plants growing in sympatry with P. crassipes. Also, gut analysis from field‐collected C. aquaticum was done to determine the ecological host range of this insect, identifying epidermal tissue of consumed plants. In no‐choice trials, survival rates of the later instars and adult C. aquaticum were similar on Pistia stratiotes L. (Araceae), Oxycaryum cubense (Poepp. & Kunth) Lye (Cyperaceae), and P. crassipes. However, under field conditions, P. crassipes and the congeneric Pontederia azurea Sw. were the only plant contents in the guts of early instars and the most abundant species in later instars and adults. The results support the hypothesis that C. aquaticum is an oligophagous insect on the genus Pontederia, and that different life stages should be considered when conducting host‐specificity trials in externally feeding mobile herbivore species. Diet composition of field‐collected insects thus could help detect false positives in laboratory trials, being an additional and realistic approach in understanding and predicting the selection processes of the insect in the new environment. Retrospective analysis of potential agents that were rejected due to lack of host‐specificity, using the methods from this study, could add a suite of additional agents to programs where invasive weeds remain unmanaged.

Entomopathogenic fungi (EF) are important biocontrol agents due to their wide host range, easy application, and compatibility with phytosanitary products. Stink bugs (Hemiptera: Pentatomidae) are the most important rice pests in Argentina. Although there is information on the pathogenicity of EF against stink bug pests in rice fields, the natural incidence of EF, and especially their association with stink bug species and plant characteristics, is largely unexplored. The aims of this study were: (1) to monitor the natural incidence of EF on Pentatomidae pests in Argentinian rice paddies; (2) to assess the relationship between the incidence of EF, stink bug feeding guild, and rice cultivar; and (3) to perform a phylogenetic analysis of the EF recorded. Sampling was conducted in target rice fields throughout the rice‐growing season (2017–2018), during which adult individuals of Tibraca limbativentris Stål and Oebalus spp. were manually collected and visually examined for evidence of mycelial development. Of the 780 individuals examined, 182 infected individuals were recorded, from which 12 strains of EF were isolated and identified based on molecular characterization: three strains of Beauveria bassiana sensu lato (Bals.‐Criv.) Vuill., five of Metarhizium anisopliae s.l. (Metschn.) Sorokin, and four of Purpureocillium lilacinum (Thom) Luangsa‐ard et al. (Hypocreales). The occurrence of the three EF species was significantly higher in stem‐feeding T. limbativentris than in seed‐feeding Oebalus spp., thus, differed between feeding guilds. For T. limbativentris, the occurrence of EF was higher when feeding on a short than on a tall rice variety, thus, differed between plant varieties. The results illustrate the potential of using native strains of EF in integrated management of stink bugs in rice.