Local dispersal pathways during the invasion of the cactus moth, Cactoblastis cactorum, within North America and the Caribbean.

Cactoblastis cactorum, a species of moth native to Argentina, feeds on several prickly pear cactus species (Opuntia) and has been successfully used as a biological control of invading Opuntia species in Australia, South Africa and native ruderal Opuntia species in some Caribbean islands. Since its introduction to the Caribbean its spread was uncontrolled, invading successfully Florida, Texas and Louisiana. Despite this long history of invasion, we are still far from understanding the factors determining the patterns of invasion of Cactoblastis in North America. Here, we explored three non-mutually exclusive explanations: a) a stepping stone model of colonization, b) long distance colonization due to hurricanes, and/or c) hitchhiking through previously reported commercial routes. Genetic diversity, genetic structure and the patterns of migration among populations were obtained by analyzing 10 nuclear microsatellite loci. Results revealed the presence of genetic structure among populations of C. cactorum in the invaded region and suggest that both marine commercial trade between the Caribbean islands and continental USA, as well as recurrent transport by hurricanes, explain the observed patterns of colonization. Provided that sanitary regulations avoiding human-mediated dispersal are enforced, hurricanes probably represent the most important agent of dispersal and future invasion to continental areas.

Developmental and Transcriptomal Responses to Seasonal Dietary Shifts in the Cactophilic Drosophila mojavensis of North America.

Drosophila mojavensis normally breeds in necrotic columnar cactus, but they also feed and breed in Opuntia fruit (prickly pear) which serves as a seasonal resource. The prickly pear fruits (PPFs) are much different chemically from cacti, mainly in their free sugars and lipid content, raising the question of the effects of this seasonal shift on fitness and on gene expression. Here we reared 3 isofemale strains of D. mojavensis collected from different parts of the species' range on semi-natural medium of either cactus or PPF and measured the development time, survival, body weights, and desiccation resistance. All these parameters were affected by diet and by interaction with strain and or sex. Interestingly, however, there appear to be tradeoffs: flies developed faster in prickly pear and the emerging adults were heavier, but those having grown in cactus were more resistant to desiccation. We also evaluated the gene expression of emerging male and female adult flies using RNA-Seq. While more genes were down-regulated in PPF than up-regulated in both sexes, the sexes did differ in expression patterns. The majority of the genes that were preferentially expressed comparing PPF versus cactus underlie metabolism. Genes involved with carbohydrate and lipid metabolism, as well as with the amino acid serine, and their relationship to growth and development reflect the ways in which these dietary differences affect the flies.

Morphological and molecular characterization of a new succulenticolous Physarum (Myxomycetes, Amoebozoa) with unique polygonal spores linked in chains.

A new plasmodiocarpic and sporocarpic species of myxomycete in the genus Physarum is described and illustrated. This new species appeared on decayed leaves and remains of succulent plants (Agave, Opuntia, Yucca) growing in arid zones. It differs from all other species in the genus in having polyhedral spores linked in chains like a string of beads, a unique feature within all known myxomycetes. Apart from detailed morphological data, partial sequences of both the small-subunit ribosomal RNA and elongation factor 1-alpha genes, generated from four isolates collected in two distant regions, i.e., Mexico and Canary Islands, are also provided in this study. Combined evidence supports the identity of the specimens under study as a new species.

The matrix alters the role of path redundancy on patch colonization rates.

Landscape connectivity is central to many problems in ecology and conservation. Recently, the role of path redundancies on movement of organisms has been emphasized for understanding connectivity, because increasing the number of potential paths (i.e., redundancy) is predicted to increase movement rates, which can alter predictions for foraging theory and population dynamics. Nonetheless, experiments that test for the effects of path redundancies on connectivity remain scarce. We tested for the role of path redundancies on the movements of a habitat specialist, Chelinidea vittiger, using experimental arenas that altered path redundancy by varying the amount and configuration of stepping stones across a gradient of matrix resistance. We found that stepping-stone redundancies increased colonization rates to target patches, but the effects differed depending on the configuration of redundancy and the structure of the matrix. In addition, matrix effects were better explained through the use of effective distance measures that incorporate redundancy in the matrix than those that ignore redundancy. Our results provide experimental evidence that measures that ignore redundancies may be inadequate for capturing functional connectivity, illustrate the ways in which redundancies alter colonization rates, and emphasize how habitat configuration and matrix structure can interact to guide movement of individuals across landscapes.

Predation potential of Chilocorus cacti (Coleoptera: Coccinellidae) to the prickly pear cacti pest Dactylopius opuntiae (Hemiptera: Dactylopiidae).

Functional response of the predator Chilocorus cacti (Linnaeus) (Coleoptera: Coccinellidae) on five densities of Dactylopius opuntiae (Cockerell) (Hemiptera: Dactylopiidae) female adults was assessed under laboratory conditions. The searching efficiency of C. cacti significantly decreased as prey density increased. The logistic regression for the predator had a negative and significant linear parameter indicating a type II functional response. Non-linear regression for Holling predator equation estimated a handling time of 1.79 ± 0.129 h and attack rate coefficient of 0.1003 ± 0.030. Most of this handling time was because the predator spent a lot of time removing the waxy coating that protects adult females of D. opuntiae. Chilocorus cacti consumes females of D. opuntiae in their reproductive stage; therefore, it could be an effective natural enemy to suppress or regulate low density populations of D. opuntiae, preventing them to reach high densities.

Development of cell lines from the cactophagous insect: Cactoblastis cactorum (Lepidoptera: Pyralidae) and their susceptibility to three baculoviruses.

The unintentional introduction of the cactus moth, Cactoblastis cactorum, a successful biological control agent formerly employed in the control of invasive prickly pear cactus species (Opuntia spp.) in Australia, Hawaii, South Africa, and various Caribbean islands, has posed great concern as to the possible threat to native, endangered species of cactus in the southeastern USA as well as with the potential to cause a major infestation of commercial and agricultural cactus crops in Mexico. A number of control measures have been investigated with varying degrees of success including, field exploration for cactus moth-specific parasitoids, insecticides, fungal, bacterial, and nematode agents. Current tactics used by the USA-Mexico binational program to eradicate cactus moth from Mexico and mitigate its westward movement in the USA include host plant removal, the manual removal and destruction of egg sticks and infected cacti stems, and the Sterile Insect Technique. One other approach not taken until now is the development of a cactus moth cell line as a tool to facilitate the investigation of baculoviruses as an alternative biocontrol method for the cactus moth. Consequently, we established C. cactorum cell lines derived from adult ovarian tissue designated as BCIRL-Cc-AM and BCIRL-Cc-JG. The mean cell population doubling time was 204.3 and 112 h for BCIRL-Cc-AM and BCIRL-Cc-JG, respectively, with weekly medium change, while the doubling time was 176.6 and 192.6 h for BCIRL-Cc-AM and BCIRL-Cc-JG, respectively, with a daily change of medium. In addition, the daily versus weekly change in medium was reflected in the percentage viability with both cell lines showing higher levels with a daily medium change. Of the three baculoviruses tested, only the recombinant AcMNPV-hsp70Red and GmMNPV at a multiplicity of infection (MOI) of 1.0 were able to demonstrate significant production of extracellular virus (ECV) in each of the cell lines, whereas both cell lines were refractive to an HzSNPV challenge at an MOI of 10. In this study, we have demonstrated both the successful development of a C. cactorum cell line and its ability to support a complete baculovirus infection. The potential is also there to pursue further investigations to determine the susceptibility of the cactus moth cell line to other viruses. Additionally, the availability of a cactus moth cell line will facilitate the analysis of viruses prior to using the more expensive bioassay test. Finally, it is hoped with the knowledge presented here that baculoviruses may also be considered as an alternative biocontrol method for the cactus moth.

Native ecotypic variation and the role of host identity in the spread of an invasive herbivore, Cactoblastis cactorum.

Environmental niche models (ENMs) have gained enormous popularity as tools to investigate potential changes in species distributions resulting from climate change and species introductions. Despite recognition that species interactions can influence the dynamics of invasion spread, most implementations of ENMs focus on abiotic factors as the sole predictors of potential range limits. Implicit in this approach is the assumption that biotic interactions are relatively unimportant, either because of scaling issues, or because fundamental and realized niches are equivalent in a species' native range. When species are introduced into exotic landscapes, changes in biotic interactions relative to the native range can lead to occupation of different regions of niche space and apparent shifts in physiological tolerances. We use an escaped biological control organism, Cactoblastis cactorum (Berg.), to assess the role of the environmental envelope as compared with patterns of host-herbivore associations based on collections made in the native range. Because all nonnative populations are derived from a single C. cactorum ecotype, we hypothesize that biotic interactions associated with this ecotype are driving the species' invasion dynamics. Environmental niche models constructed from known native populations perform poorly in predicting nonnative distributions of this species, except where there is an overlap in niche space. In contrast, genetic isolation in the native range is concordant with the observed pattern of host use, and strong host association has been noted in nonnative landscapes. Our results support the hypothesis that the apparent shift in niche space from the native to the exotic ranges results from a shift in biotic interactions, and demonstrate the importance of considering biotic interactions in assessing the risk of future spread for species whose native range is highly constrained by biotic interactions.

Host plant adaptation in Drosophila mettleri populations.

The process of local adaptation creates diversity among allopatric populations, and may eventually lead to speciation. Plant-feeding insect populations that specialize on different host species provide an excellent opportunity to evaluate the causes of ecological specialization and the subsequent consequences for diversity. In this study, we used geographically separated Drosophila mettleri populations that specialize on different host cacti to examine oviposition preference for and larval performance on an array of natural and non-natural hosts (eight total). We found evidence of local adaptation in performance on saguaro cactus (Carnegiea gigantea) for populations that are typically associated with this host, and to chemically divergent prickly pear species (Opuntia spp.) in a genetically isolated population on Santa Catalina Island. Moreover, each population exhibited reduced performance on the alternative host. This finding is consistent with trade-offs associated with adaptation to these chemically divergent hosts, although we also discuss alternative explanations for this pattern. For oviposition preference, Santa Catalina Island flies were more likely to oviposit on some prickly pear species, but all populations readily laid eggs on saguaro. Experiments with non-natural hosts suggest that factors such as ecological opportunity may play a more important role than host plant chemistry in explaining the lack of natural associations with some hosts.

First record of Hesperolabops nigriceps Reuter (Hemiptera: Miridae) on Opuntia ficus-indica in Milpa Alta, Mexico City.

In recent years a species of Hesperolabops has become a problem as a pest of nopalitos, Opuntia ficus-indica, in Milpa Alta, in the south of Mexico City, which is the most important production region of this vegetable in the country. A survey of Hesperolabops in Milpa Alta has resulted in the first report of Hesperolabops nigriceps Reuter. This occurrence should be monitored and considered in future studies in order to avoid misidentification of Hesperolabops spp. Kirkaldy native populations there, and to avoid the confusion of the damage that may be caused on O. ficus-indica.

First record of Hesperolabops nigriceps Reuter (Hemiptera: Miridae) on Opuntia ficus-indica in Milpa Alta, Mexico City

In recent years a species of Hesperolabops has become a problem as a pest of nopalitos, Opuntia ficus-indica, in Milpa Alta, in the south of Mexico City, which is the most important production region of this vegetable in the country. A survey of Hesperolabops in Milpa Alta has resulted in the first report of Hesperolabops nigriceps Reuter. This occurrence should be monitored and considered in future studies in order to avoid misidentification of Hesperolabops spp. Kirkaldy native populations there, and to avoid the confusion of the damage that may be caused on O. ficus-indica.

Targets of an invasive species: oviposition preference and larval performance of Cactoblastis cactorum (Lepidoptera: Pyralidae) on 14 North American opuntioid cacti.

Cactoblastis cactorum Berg (Lepidoptera: Pyralidae), the cactus moth, is a well-known biological control agent of prickly pear cactus (Cactaceae: Opuntia Miller). The arrival of the moth in Florida and its subsequent spread through the southeastern United States poses a threat to opuntioid diversity in North America. Of particular concern are the ecological and economic impacts the moth could have in the southwestern United States and Mexico, where both native and cultivated Opuntia species are important resources. It is unknown which species would best support larval development if the moth were to spread further westward in North America. This study aimed to determine if ovipositing females demonstrate preferences for any of 14 common opuntioids native to or naturalized in Mexico and the southwestern United States; which of these opuntioids best support larval development; and if oviposition preference correlates with larval performance, as predicted by simple adaptive models. Results from a field experiment showed that female moths preferred O. engelmannii Salm-Dyck ex Engelmann variety linguiformis (Griffiths) Parfitt and Pinkava and O. engelmannii variety engelmannii for oviposition. A generalized linear model showed number of cladodes and degree of spininess to be significant predictors of oviposition activity. Results from a no-choice larval survival experiment showed Consolea rubescens (Salm-Dyck ex de Candolle.) Lemaire and O. streptacantha Lemaire to be the best hosts. Epidermal toughness was a significant predictor of most larval fitness parameters. In general, oviposition preference was not correlated with larval performance. A lack of co-evolutionary history between C. cactorum and North American opuntioid species may help explain this disconnect.

Identification of factors influencing flight performance of field-collected and laboratory-reared, overwintered, and nonoverwintered cactus moths fed with field-collected host plants.

Environmental conditions during egg and larval development may influence the dispersal ability of insect pests, thus requiring seasonal adjustment of control strategies. We studied the longest single flight, total distance flown, and the number of flights initiated by wild Cactoblastis cactorum (Berg) (Lepidoptera: Pyralidae) to determine whether the flight performance of overwintered cactus moths with a prolonged feeding phase during development differs from nonoverwintered cactus moths. Pupae of field-collected and laboratory-reared moths were transported together from the United States to Switzerland, and flight mills were used to characterize the flight capacity of 24- to 48-h-old adults during their most active period of the diel cycle. The lack of seasonal variation in flight performance of those moths that developed under controlled environment but were fed with field-collected Opuntia cacti showed that seasonal changes in host plant quality did not affect flight. This consistent flight performance in the mass-reared laboratory population throughout the year is beneficial for sterile insect technique programs, which aim to limit the dispersal of this pest. For field-collected C. cactorum, the larger overwintered females performed similarly to nonoverwintered females, indicating that longer feeding time at lower temperature increases body size but does not influence female flight capacity. Young mated females had a similar flight capacity to unmated ones, suggesting that gravid females may play an important role in invading new habitats. For males, overwintering increased the proportion of long-distance flyers, suggesting that they are well-adapted to locate the more sparsely dispersed females in the spring.

Herbivore-mediated ecological costs of reproduction shape the life history of an iteroparous plant.

Plant reproduction yields immediate fitness benefits but can be costly in terms of survival, growth, and future fecundity. Life-history theory posits that reproductive strategies are shaped by trade-offs between current and future fitness that result from these direct costs of reproduction. Plant reproduction may also incur indirect ecological costs if it increases susceptibility to herbivores. Yet ecological costs of reproduction have received little empirical attention and remain poorly integrated into life-history theory. Here, we provide evidence for herbivore-mediated ecological costs of reproduction, and we develop theory to examine how these costs influence plant life-history strategies. Field experiments with an iteroparous cactus (Opuntia imbricata) indicated that greater reproductive effort (proportion of meristems allocated to reproduction) led to greater attack by a cactus-feeding insect (Narnia pallidicornis) and that damage by this herbivore reduced reproductive success. A dynamic programming model predicted strongly divergent optimal reproductive strategies when ecological costs were included, compared with when these costs were ignored. Meristem allocation by cacti in the field matched the optimal strategy expected under ecological costs of reproduction. The results indicate that plant reproductive allocation can strongly influence the intensity of interactions with herbivores and that associated ecological costs can play an important selective role in the evolution of plant life histories.

Wing morphology and fluctuating asymmetry depend on the host plant in cactophilic Drosophila.

As in most insect groups, host plant shifts in cactophilic Drosophila represent environmental challenges as flies must adjust their developmental programme to the presence of different chemical compounds and/or to a microflora that may differ in the diversity and abundance of yeasts and bacteria. In this context, wing morphology provides an excellent opportunity to investigate the factors that may induce changes during development. In this work, we investigated phenotypic plasticity and developmental instability of wing morphology in flies on the cactophilic Drosophila buzzatii and Drosophila koepferae raised on alternative breeding substrates. We detected significant differences in wing size between and within species, and between flies reared on different cactus hosts. However, differences in wing shape between flies emerged from different cactus hosts were not significant either in D. buzzatii or in D. koepferae. Our results also showed that morphological responses involved the entire organ, as variation in size and shape correlated between different portions of the wing. Finally, we studied the effect of the rearing cactus host on developmental instability as measured by the degree of fluctuating asymmetry (FA). Levels of FA in wing size were significantly greater in flies of both species reared in non-preferred when compared with those reared in preferred host cacti. Our results are discussed in the framework of an integrative view aimed at investigating the relevance of host plant shifts in the evolution of the guild of cactophilic Drosophila species that diversified in South America.

Demographic models reveal the shape of density dependence for a specialist insect herbivore on variable host plants.

1. It is widely accepted that density-dependent processes play an important role in most natural populations. However, persistent challenges in our understanding of density-dependent population dynamics include evaluating the shape of the relationship between density and demographic rates (linear, concave, convex), and identifying extrinsic factors that can mediate this relationship. 2. I studied the population dynamics of the cactus bug Narnia pallidicornis on host plants (Opuntia imbricata) that varied naturally in relative reproductive effort (RRE, the proportion of meristems allocated to reproduction), an important plant quality trait. I manipulated per-plant cactus bug densities, quantified subsequent dynamics, and fit stage-structured models to the experimental data to ask if and how density influences demographic parameters. 3. In the field experiment, I found that populations with variable starting densities quickly converged upon similar growth trajectories. In the model-fitting analyses, the data strongly supported a model that defined the juvenile cactus bug retention parameter (joint probability of surviving and not dispersing) as a nonlinear decreasing function of density. The estimated shape of this relationship shifted from concave to convex with increasing host-plant RRE. 4. The results demonstrate that host-plant traits are critical sources of variation in the strength and shape of density dependence in insects, and highlight the utility of integrated experimental-theoretical approaches for identifying processes underlying patterns of change in natural populations.

Postharvest heat and cold treatment to control Ceratitis capitata on cactus pear fruit.

In order to work out a quarantine treatment for cactus pear fruit a factorial experimental plan was carried combining postharvest water dips at 20, 50, 54, 58 and 60 degrees C and storage at 1 degrees C for 3, 6 and 10 days. Cactus pear fruit cv 'Rossa' were artificially infested with Med. fly eggs (at least 20 eggs per fruit) then left in the lab at 25 degrees C for 4 days. Treatments took place by dipping the fruit at each water temperature for 2 mm. At each established time fruit was picked and checked for vital larvae and degree of chilling injury (CI). Probit 9 requirements were achieved in all cases when fruit was cold-stored for 10 days. When fruit was kept for 6 days the quarantine requirement was achieved only by dipping the fruit at 58 and 60 degrees C while none dip treatment was effective if fruit was stored for 3 days at 1 degrees C. All Fruit stored for 10 days at 1 degrees C showed severe CI symptoms and when kept for 6 days the same degree of CI was found on fruit dipped in water at 20, 58 and 60 degrees C. No CI was observed after 3 days at 1 degrees C. In conclusion only when fruit was dipped at 50-54 degrees C and stored for 10 days at 1 degrees C the probit 9 condition was attained with acceptable CI symptoms.