Christopher P. Brooks

Spatial and Temporal Heterogeneity Explain Disease Dynamics in a Spatially Explicit Network Model

There is an increasing recognition that individual‐level spatial and temporal heterogeneity may play an important role in metapopulation dynamics and persistence. In particular, the patterns of contact within and between aggregates (e.g., demes) at different spatial and temporal scales may reveal important mechanisms governing metapopulation dynamics. Using 7 years of data on the interaction between the anther smut fungus (Microbotryum violaceum) and fire pink (Silene virginica), we show how the application of spatially explicit and implicit network models can be used to make accurate predictions of infection dynamics in spatially structured populations. Explicit consideration of both spatial and temporal organization reveals the role of each in spreading risk for both the host and the pathogen. This work suggests that the application of spatially explicit network models can yield important insights into how heterogeneous structure can promote the persistence of species in natural landscapes.

Geographic patterns of genetic diversity from the native range of Cactoblastis cactorum (Berg) support the documented history of invasion and multiple introductions for invasive populations

Spread of the invasive cactus-feeding moth Cactoblastis cactorum has been well documented since its export from Argentina to Australia as a biocontrol agent, and records suggest that all non-native populations are derived from a single collection in the moth’s native range. The subsequent global spread of the moth has been complex, and previous research has suggested multiple introductions into North America. There exists the possibility of additional emigrations from the native range in nursery stock during the late twentieth century. Here, we present mitochondrial gene sequence data (COI) from South America (native range) and North America (invasive range) to test the hypothesis that the rapid invasive spread in North America is enhanced by unique genetic combinations from isolated portions of the native range. We found that haplotype richness in the native range of C. cactorum is high and that there was 90% lower richness in Florida than in Argentina. All Florida C. cactorum haplotypes are represented in a single, well-defined clade, which includes collections from the reported region of original export from Argentina. Thus, our data are consistent with the documented history suggesting a single exportation of C. cactorum from the eastern region of the native range. Additionally, the presence of geographic structure in three distinct haplotypes within the same clade across Florida supports the hypothesis of multiple introductions into Florida from a location outside the native range. Because the common haplotypes in Florida are also known to occur in the neighboring Caribbean Islands, the islands are a likely source for independent North American colonization events. Our data show that rapid and successful invasion within North America cannot be attributed to unique genetic combinations. This suggests that successful invasion of the southeastern US is more likely the product of a fortuitous introduction into favorable abiotic conditions and/or defense responses of specific Opuntia hosts, rapid adaptation, or a release from native enemies.

The role of demography and markets in determining deforestation rates near Ranomafana National Park, Madagascar.

The highland forests of Madagascar are home to some of the worlds most unique and diverse flora and fauna and to some of its poorest people. This juxtaposition of poverty and biodiversity is continually reinforced by rapid population growth, which results in increasing pressure on the remaining forest habitat in the highland region, and the biodiversity therein. Here we derive a mathematical expression for the subsistence of households to assess the role of markets and household demography on deforestation near Ranomafana National Park. In villages closest to urban rice markets, households were likely to clear less land than our model predicted, presumably because they were purchasing food at market. This effect was offset by the large number of migrant households who cleared significantly more land between 1989–2003 than did residents throughout the region. Deforestation by migrant households typically occurred after a mean time lag of 9 years. Analyses suggest that while local conservation efforts in Madagascar have been successful at reducing the footprint of individual households, large-scale conservation must rely on policies that can reduce the establishment of new households in remaining forested areas.

The Role of Host Identity in Determining the Distribution of the Invasive Moth Cactoblastis Cactorum (Lepidoptera: Pyralidae) in Florida

ABSTRACT We examined the association between the exotic South American cactus moth, Cactoblastis cactorum (Berg) (Lepidoptera: Pyralidae), and its host plants (prickly pear cacti, subfamily Opuntioideae) in Florida to assess the role of host plant identity and local host community on the prevalence of this invasive moth. From May to September 2008, we surveyed 4,243 plants across 165 sites throughout Florida for C. cactorum. The probability of C. cactorum presence at a particular site was best explained by the presence of either Opuntia humifusa var. ammophila (Small) L. D. Benson or O. stricta (Haworth) Haworth. Within infested sites, only O. stricta individuals were significantly more infested than other host plants. Our results suggest that understanding patterns of C. cactorum infestation, both in Florida and as it spreads towards the western United States relies, at least in part, on determining the mechanism by which O. stricta influences the suitability of specific host communities.

Larval morphology and host use confirms ecotypic variation in Cactoblastis cactorum (Berg)

Despite their recognized importance in the literature, the contribution of native-range species interactions to invasion success has been inadequately studied. Previous authors have suggested that biases in the sampling of propagules from the native range might influence invasion success, but most contemporary invasion hypotheses focus on the development of novel interactions or a release from native consumers and competitors. When ecotypic variation exists in native host-consumer associations, the specific pattern of sampling across ecotypes could determine invasion success, especially when the genetic diversity among exotic propagules is low. The South American cactus moth, Cactoblastis cactorum (Berg), is an oligophagous consumer whose larvae feed on prickly pear cacti (subfamily Opuntioideae). The moth was collected from a small geographic area along the Argentina-Uruguay border in 1925 and was introduced to multiple continents as a biological control species, which has subsequently invaded North America. Here we show that groups defined by genetic structure in this species’ native range are concordant with distinct patterns of host association and larval morphology. Furthermore, in Florida populations, morphological traits have diverged from those found in the native range, and patterns of host association suggest that strong biases in host preference also occur in invasive populations. The documented history of C. cactorum introductions confirms that multiple attempts were made to export the moth, but that only a single ecotype was exported successfully. Additional work will be necessary to determine whether the observed host biases in North America reflect a rapid adaptation to naïve hosts or a conservation of traits related to specific aspects of the host-consumer association.

Covariance between predation risk and nutritional preferences confounds interpretations of giving‐up density experiments

Giving-up density (GUD) experiments have been a foundational method to evaluate perceived predation risk, but rely on the assumption that food preferences are absolute, so that areas with higher GUDs can be interpreted as having higher risk. However, nutritional preferences are context dependent and can change with risk. We used spiders and grasshoppers to test the hypothesis that covariance in nutritional preferences and risk may confound the interpretation of GUD experiments. We presented grasshoppers with carbohydrate-rich and protein-rich diets, in the presence and absence of spider predators. Predators reduced grasshopper preference for the protein-rich food, but increased their preference for the carbohydrate-rich food. We then measured GUDs with both food types under different levels of risk (spider density, 0-5). As expected, GUDs increased with spider density indicating increasing risk, but only when using protein-rich food. With carbohydrate-rich food, GUD was independent of predation risk. Our results demonstrate that predation risk and nutritional preferences covary and can confound interpretation of GUD experiments.

Phylogeographic evidence for a Florida panhandle–peninsula discontinuity in the distribution of Melitara prodenialis Walker (Lepidoptera: Pyralidae), a native cactus-boring moth

Insects are highly underrepresented in the phylogeographic literature of the coastal plain region of the southeastern U.S., but they may contribute much to understanding the phylogeographic history of the area. The present study uses Melitara prodenialis Walker, a cactus‐boring moth, to test two alternative hypotheses: Pleistocene changes in environment and coastline associated with population geographic change resulted in (i) a homogeneous Florida, USA, population of M. prodenialis or (ii) isolated subpopulations that gave rise to genetic divergence between regions. Melitara prodenialis larvae were collected from 23 sites (n = 42 larvae sampled). For each larva, a 791 bp sequence of the COI mitochondrial gene was sequenced. Bayesian and parsimony approaches were used to investigate relationships among haplotypes. Phylogeographic and demographic analyses were conducted to identify geographic patterns in haplotype diversity distribution and infer population dynamics over time. Bioclim climate variables from the last interglacial period and the present were used to assess the potential contribution of environmental conditions to phylogeographic patterns observed. Melitara prodenialis populations in the Florida panhandle and peninsula are distinct, and the geographic segregation between these regions is correlated with current and historic climate patterns. Results suggest that populations of M. prodenialis in the Florida peninsula have more recently expanded than those in the panhandle. These findings are consistent with M. prodenialis populations changing in size and distribution following land area and climatic shifts associated with North American cycles of glaciation, with panhandle and peninsula populations remaining segregated over the relevant timeframes.

First Records of The Parasitoid Temelucha sinuata Cushman (Hymenoptera: Ichneumonidae) in Mississippi and Florida, U.S.A.

Larvae of the native eastern blue cactus borer Melitara prodenialis Walker (Lepidoptera: Pyralidae) were collected on single occasions from cladodes of prickly-pear cactus (Opuntia spp.) at Sweetwater (Liberty Co.), Florida (30. 50483N, 84.95512W), in April 2009 and Town Creek Campground, West Point (Clay Co.), Mississippi (33.60667N, 88.49195W) in July 2011. A total of 91 larvae were collected from the Mississippi location, but the total number of Florida larvae collected is unknown. The larvae from Florida were provisioned with wild-collected cladodes of O. humifusa var. humifusa and reared at 26.7°C, whereas the Mississippi larvae were provisioned with wild-collected O. pusilla and reared at 28°C. Both collections were maintained at ~70% relative humidity and on a 12:12 day-night cycle. Two female and 28 mixed sex (20 male, 8 female) parasitoid wasps eclosed from the M. prodenialis pupae reared from the Florida and Mississippi collections, respectively. The wasps from Florida were identified as Temelucha sinuata Cushman (Hymenoptera: Ichneumonidae) by Rob ert Kula, USDA-ARS Systematic Entomology Laboratory. The wasps from Mississippi were identified as T. sinuata by R. Brown, Mississippi Ento molog ical Museum, based on their similarity to the Florida specimens. Wasps from both collections have similar body size and color, and a sinuous ovipositor consistent with the descriptions of Cushman (1926) and Dasch (1979). Voucher speci mens from the Florida and Mississippi collections have been deposited in the Mississippi Entomological Museum (Fig. 1). The previous known distribution of T. sinuata has been reported as ranging from California, Arizona, Texas, and Arkansas to the Yucatan of Mexico (Dasch 1979, Carlton and Kring 1994, Gonzalez-Moreno and Bordera 2011). This report represents the first records of T. sinuata from Mississippi and Florida. Parasitoids of the subfamily Cremastinae, of which T. sinuata is a member, frequently parasitize pyralid moths, as well as other lepidopterans (Cushman 1926, Dodd 1940, Dasch 1979). Temelucha sinuata has only been collected from pyralid hosts: Cactobrosis strigalis and Rumatha glaucatella (Dasch 1979), in 376 ENTOMOLOGICAL NEWS

Using MODIS land-use/land-cover data and hydrological modeling for estimating nutrient concentrations

This paper presents results on nutrient concentrations estimations in the Upper Tombigbee watershed (northern Mississippi-Alabama region, USA). It details the hydrological model development and its use for providing stream flow, runoff, and nutrient concentrations (total phosphorus, TP, and total nitrogen, TN) for subsequent biological studies. Geographical locations of data collection on fish and mussel were used to perform a watershed delineation of the area of study. The delineated catchment was enriched with land use information from USGS GIRAS (1986) and NASA MODIS MOD12Q1 (2001-2004) datasets. An increase of 34% in agricultural lands is shown to have occurred from 1986 to 2003. The Hydrological Program Fortran (HSPF) was used for estimating stream flow and run-off rates for two hydrological models (one per each land use dataset). Export coefficients representative for the regions were used for estimating TN and TP concentrations. It is shown that only maximum concentrations of total nitrogen and total phosphorus have increased from 1986 to 2003. The percent increase ranges from 5 to 16% when comparing a sub-set of sub-basins, and 34% to 37% when taking into account all sub-basins. This seems to be consistent with the increase in agricultural areas in the same time period.