Browsing by Author "Littlefield, Jeffrey L."

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The effects of intraspecific hybridization on the host specificity of a weed biocontrol agent
(Elsevier BV, 2021-06) Szűcs, M.; Clark, E.I.; Schaffner, U.; Littlefield, Jeffrey L.; Hoover, C.; Hufbauer, R.A.
Hybridization can alter the host-specificity and fitness of herbivorous insects when the hybridizing populations are adapted to different hosts. It is less clear what the effects of admixture may be when genetically distinct populations are crossed that have similar and narrow host ranges. We tested the effects of hybridization between an Italian and Swiss population of the ragwort flea beetle, Longitarsus jacobaeae, a biocontrol agent for tansy ragwort, Jacobaea vulgaris, in the USA. Development success, development time, and fecundity of parental and first- and second-generation hybrids were assessed on the primary host and ten closely related plant species in no-choice larval transfer experiments. Four of the non-target species supported limited development but none represented novel host use of hybrids compared to the parents. Development time showed maternal effects on one of the non-target species where offspring of crosses with Italian mother developed slower. Percent larval development was significantly greater for one replication of a non-target species, indicating a plant genotype effect. Overall, hybridization did not result in changes of the fundamental host range or improved performance of hybrids on non-target species even when some hybrid lineages exhibited hybrid vigor on the primary host. These findings underscore the reliability of currently-employed host-specificity testing procedures that identify the fundamental host range of potential agents. Our results also support the newly advocated approach to promote intraspecific hybridization in biocontrol agents when the parental populations have similar and narrow host ranges to increase genetic variation and create novel genotypes to facilitate adaptation and persistence in the new range.
Eriophyid Mites in Classical Biological Control of Weeds: Progress and Challenges
(MDPI AG, 2021-06) Marini, Francesca; Weyl, Philip; Vidović, Biljana; Petanović, Radmila; Littlefield, Jeffrey L.; Simoni, Sauro; de Lillo, Enrico; Cristofaro, Massimo; Smith, Lincoln
A classical biological control agent is an exotic host-specific natural enemy, which is intentionally introduced to obtain long-term control of an alien invasive species. Among the arthropods considered for this role, eriophyid mites are likely to possess the main attributes required: host specificity, efficacy, and long-lasting effects. However, so far, only a few species have been approved for release. Due to their microscopic size and the general lack of knowledge regarding their biology and behavior, working with eriophyids is particularly challenging. Furthermore, mites disperse in wind, and little is known about biotic and abiotic constraints to their population growth. All these aspects pose challenges that, if not properly dealt with, can make it particularly difficult to evaluate eriophyids as prospective biological control agents and jeopardize the general success of control programs. We identified some of the critical aspects of working with eriophyids in classical biological control of weeds and focused on how they have been or may be addressed. In particular, we analyzed the importance of accurate mite identification, the difficulties faced in the evaluation of their host specificity, risk assessment of nontarget species, their impact on the weed, and the final steps of mite release and post-release monitoring.
Temporal and density dependent impacts of an invasive plant on pollinators and pollination services to a native plant
(2016-02) Herron-Sweet, Christina R.; Lehnhoff, Erik A.; Burkle, Laura A.; Littlefield, Jeffrey L.; Mangold, Jane M.
Pollinators and pollination services are under threat globally, and invasive plants have been implicated in their decline. Results of previous studies suggest that consequences of invasion for pollinators and plant–pollinator interactions are context specific. Investigating factors such as the density of an invasive plant and its phenology may provide a nuanced understanding of invasive species impacts. We conducted a 2-yr study in Montana to investigate how local pollinator abundance, richness, community composition, and visitation patterns varied with invasive Centaura stoebe density and phenology, and whether C. stoebe altered the reproduction of a co-flowering native plant, Heterotheca villosa, through changes in pollinator visitation. In an observational study, we found that during its peak bloom in August, Centaurea stoebe provided abundant floral resources to late-season pollinators. However, prior to C. stoebe bloom, native floral density and pollinator abundance and richness of these plots were lower compared to plots where C. stoebe was low or absent. Pollinator community composition in plots without C. stoebe was different compared to plots with C. stoebe (both high and low C. stoebe density), and these differences in pollinator composition strongly depended on the time of season. In an experimental study, we found that there was little evidence of competition between C. stoebe and H. villosa for pollinators at low relative densities of C. stoebe. Using experimental pollen supplementation, we observed no evidence of pollen limitation of seed set in H. villosa with increasing density of experimentally added C. stoebe. Our results suggest that the impact of an invasive plant on pollinators and plant–pollinator interactions depends on the relative density of the invasive plant and the timing of its bloom. Differences in pollinator visitation patterns over the growing season suggest that although C. stoebe provides abundant resources to late-season pollinators, displacement of native plants at high C. stoebe density may indirectly harm pollinators that are active before C. stoebe blooms or that prefer native plants. Based on our results, restricting C. stoebe to low densities may help mitigate negative repercussions to native plant reproduction and may even be beneficial to some pollinators.
Variation in reproductive mode across the latitudinal range of invasive Russian knapweed
(Oxford University Press, 2022-07) Gaskin, John F.; Littlefield, Jeffrey L.; Rand, Tatyana A.; West, Natalie M.
For invading species, reproduction is a critical determinant of population establishment as well as spread into new areas. When species have multiple modes of reproduction, the prevalence of different modes can influence management decisions. We used genetic markers to determine the prevalent method of recruitment for invasive Russian knapweed (Acroptilon repens). This species forms patches and can spread by both rhizomic growth and seed from outcrossing. We found no shared genotypes between 41 western North American populations, indicating at the macroscale, Russian knapweed is spreading via seed to distant locations. We also examined drivers of reproductive mode by comparing clonality with large-scale environmental factors across the invasion. We found a correlation between latitude and clonal versus seed reproduction, with clonality higher in northern latitude populations. This trend was associated most parsimoniously with decreasing maximum annual temperature and 30-year average of available growing degree days, and increasing soil organic carbon content. These results have management implications: if not properly temporally implemented, grazing or herbicide applications that create open spaces for recruitment may increase the likelihood of Russian knapweed patch persistence through seed, and recently released galling biological control agents in North America may be less effective in northern latitudes where Russian knapweed spread by seed is less prevalent.