Cactoblastis Cactorum Research Articles

The Role of Host Identity in Determining the Distribution of the Invasive MothCactoblastis cactorum(Lepidoptera: Pyralidae) in Florida

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.

Selecting for Tolerance against Pathogens and Herbivores to Enhance Success of Reintroduction and Translocation

Some species have insufficient defenses against climate change, emerging infectious diseases, and non-native species because they have not been exposed to these factors over their evolutionary history, and this can decrease their likelihood of persistence. Captive breeding programs are sometimes used to reintroduce individuals back into the wild; however, successful captive breeding and reintroduction can be difficult because species or populations often cannot coexist with non-native pathogens and herbivores without artificial selection. In captive breeding programs, breeders can select for host defenses that prevent or reduce pathogen or herbivore burden (i.e., resistance) or traits that limit the effects of parasitism or herbivory on host fitness (i.e., tolerance). We propose that selection for host tolerance may enhance the success of reintroduction or translocation because tolerant hosts generally have neutral effects on introduced pathogens and herbivores. The release of resistant hosts would have detrimental effects on their natural enemies, promoting rapid evolution to circumvent the host resistance that may reduce the long-term probability of persistence of the reintroduced or translocated species. We examined 2 case studies, one on the pathogenic amphibian chytrid fungus (Batrachochytrium dendrobatidis [Bd]) and the other on the herbivorous cactus moth (Cactoblastis cactorum) in the United States, where it is not native. In each case study, we provide recommendations for how captive breeders and managers could go about selecting for host tolerance. Selecting for tolerance may offer a promising tool to rescue hosts species from invasive natural enemies as well as new natural enemies associated with climate change-induced range shifts.

Evolution and biological control

Opinions about the value of biological control are often extreme. Colloquially, biological control most often refers to classical biological control, in which one species is introduced from another region to control pests such as arthropod herbivores in agricultural systems, or weeds in managed and natural systems.1 As such, biological control has the potential to be a low-cost, chemical free, means to control pests. Numerous biological control programs have been unqualified successes (Bellows 2001), such as the control of cacti in Australia with the moth Cactoblastis cactorum (Raghu and Walton 2007), of cottony-cushion scale (Icerya purchasi) in California with the vedalia lady beetle, Rodolia cardinalis (Caltagirone and Doutt 1989), and of glassy-winged sharpshooters in French Polynesia with the egg parasitoid Gonatocerus ashmeadi (Grandgirard et al. 2009). Yet, classical biological control, as with any introduction of a species into a new area, necessarily involves the unknown and therefore carries some inherent risk (Simberloff and Stiling 1996) – what will these organisms actually do in a novel ecosystem? The most unpredictable element in biological control is the extent to which the realized niche is modified in the new environment. This effect has been responsible for some disastrous outcomes of classical biological control, many of which occurred during an era when vertebrates were being introduced around the world by Europeans for a variety of reasons (e.g., introducing the birds of Shakespeare to America, Mirsky 2008), including for biological control (Howarth 1991). The introductions as biological control agents of cane toad to Australia (Crossland et al. 2000) and mongoose to Hawaii (Hays and Conant 2007) are notorious. Introductions of generalist invertebrate agents also have had dire consequences, such as the introduction of predatory snails to French Polynesia (Murray et al. 1988; Coote 2007). In retrospect, some of the unintended consequences of biological control could have been avoided with more ecological knowledge (McEvoy and Coombs 2000) or more societal appreciation for native species (which has developed with time, Henneman and Memmott 2001), but with other introductions, it would have been impossible to know ahead of time what the risks would be (e.g., gall fly agents of knapweeds providing supplementary food to mice that harbor hantavirus, Pearson and Callaway 2006). Many of the unknown outcomes of biological control are purely ecological – what is the risk that a wasp, introduced to parasitize an agricultural pest, will also be able to feed on a native insect? Other unknowns involve evolution – will a herbivore adapt over time to be able to feed on a new nontarget host or hybridize with a closely related species? This volume explores the evolutionary aspects of biological control. Although often overlooked, evolutionary considerations are critical to all stages of classical biological control, from agent selection, to quarantine, release, establishment, and ultimately success in pest control (Ehler et al. 2004). Many questions are unresolved. For example, should agents be chosen that have a long history with the host or are ‘new associations’ more likely to succeed (Hokkanen and Pimentel 1989)? Can one improve effectiveness through artificial selection (Hopper et al. 1993)? Will postcolonization adaptation of the agent increase the likelihood of success, and/or are hosts equally likely to evolve resistance over time (Roderick 1992; Holt and Hochberg 1997; Hufbauer 2001)? Are generalist consumers more likely to survive in novel environments or are specialists more effective (Murdoch et al. 1985; Waage 1990; Brodeur 2012)? More recently, concern for the environment, as well as theory examining the reasons for success of generalist predators, prompted a shift to the release of specialized consumers typically preceded by extensive testing aimed at delimiting the host range of candidate biological control agents. While this approach has clearly made biological control more predictive ecologically, research focused on host range currently lacks measures of genetic variation in host use and responses of those hosts, and thus evolutionary uncertainties remain.

Effects of Cactoblastis cactorum on the survival and growth of North American Opuntia

Cactoblastis cactorum is known for being both a biological control agent and an invasive pest of opuntioid cacti. The spread of C. cactorum in the southeastern United States may threaten the biological and physical integrity of desert, scrub, and coastal habitats. However, the effects of invasive species are known to vary spatially and temporally, and C. cactorum’s efficacy as a biological control agent varies considerably from region to region. Therefore, the long term effects of C. cactorum within its U.S. range are still uncertain. Marked Opuntia stricta (n = 253) and O. humifusa (n = 327) plants along the west coast of Florida were censused for 6 years to determine the effects of C. cactorum attack on survival and growth rate of plants, and to examine host species differences and the effects of plant size. 78.1 % of the Opuntia plants were attacked by C. cactorum during the 6 year study and the overall survival rate was 75.8 %. Plants attacked by C. cactorum were more likely to die than unattacked plants and a plant’s odds of surviving the 6 year period decreased as C. cactorum attack frequency increased. However, plants that survived the 6 year period showed, on average, positive growth and there was no significant difference in growth rates between surviving attacked and unattacked plants. O. stricta plants were more likely to be attacked at least once, were attacked more frequently, and were more likely to die after being attacked than were O. humifusa plants. Plant size did not predict plant survival, but larger surviving plants lost proportionally more pads over the 6 years than smaller surviving plants. Although C. cactorum should still be considered a threat, particularly for rare opuntioids, overall survival along the west central Florida coast is currently high and plants that are able to survive C. cactorum attack are not being reduced in size, possibly because they possess traits that render them more tolerant of C. cactorum damage. Our findings suggest that an assumption of severe negative effects of an invasive species, based on its effects in other regions or over short periods of time, may not always be justified.

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.

Laboratory Biological Parameters ofTrichogramma fuentesi(Hymenoptera: Trichogrammatidae), an Egg Parasitoid ofCactoblastis cactorum(Lepidoptera: Pyralidae)

ABSTRACT Trichogramma fuentesi Torre was identified attacking Cactoblastis cactorum (Berg), a serious pest of Opuntia spp. in North America, raising the possibility of using this egg parasitoid as an inundative biological control agent. Studies were conducted to assess the biological parameters of this parasitoid under laboratory conditions. Nutritive quality influence of the rearing supplement on the parasitoid's longevity, mating, and age was evaluated based on the level of parasitism. The presence and type of food source had a positive impact on female longevity, and female parasitoids given a diet composed of pure honey lived the longest; an average of 11 d. Mated females parasitized a greater number of C. cactorum host eggs than did unmated females. Percent parasitism significantly decreased with female age. Two- to 3-day old female parasitoids had the highest level of parasitism. Two-day old host eggs were the optimal host egg age for parasitization by T. fuentesi. In the context of implementing an ...

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.

The South American Cactus Moth

These individuals of Cactoblastis cactorum are from the Northeastern ecotype and were found feeding on this large Opuntia ficus-indica plant near Puerto Tirol, Chaco Province, Argentina. Photograph by Christopher Brooks. Cactoblastis cactorum individuals burrow into the stem segments of Opuntia species where they feed gregariously. These individuals from the Western ecotype have hollowed out this prickly pear cactus cladode near El Quebrachal, Salta Province, Argentina. Photograph by Christopher Brooks. The South American cactus moth is a well-known insect, both because it represents one of the most successful biocontrol releases known (in Australia), and because it has now become an escaped biocontrol agent that threatens the native prickly pear diversity in the United States and Mexico. We used collections of individuals from sites across the core of the species' native range (Argentina) and from known infestations in Australia, South Africa, and Florida to show that environmental niche models do not capture the fundamental determinants of habitat. Instead it seems likely that host traits are the driving force determining the quality and availability of habitat, both within and outside of the native range. Cactoblastis cactorum individuals collected from an Opuntia ficus-indica plant near Puerto Tirol, Chaco Province, Argentina. These individuals are curled up on some dessicant that is used for rearing in the laboratory so that the unrooted, damaged cactus pads do not become too wet for the larvae. Photograph by Christopher Brooks. These photographs illustrate the article “Native ecotypic variation and the role of host identity in the spread of an invasive herbivore, Cactoblastis cactorum” by Christopher P. Brooks, Gary N. Ervin, Laura Varone, and Guillermo A. Logarzo, tentatively scheduled to appear in Ecology 93(2), February 2012.

Indian Fig Cactus (Opuntia Ficus-Indica(L.) Miller) in the Americas: an Uncertain History

Abstract: Opuntia ficus-indica (L.) Miller is a globally important cactus species with a long history of human use. In addition to the importance of O. ficus-indica as a food for humans and livestock, it also has long served a role in the production of cochineal, a once important textile dye. This cactus also is intimately interwoven into the story of Cactoblastis cactorum (Berg) (South American cactus moth), one of the best-known examples of biological weed control. In this regard, O. ficus-indica has been a target weed as well as an unintended host in C. cactorum invasion. Although the distribution and human-assisted movement of this cactus throughout much of the world is well documented, surprisingly little has been written about its history and movement within the Americas. Literature associated with Opuntia and their phytophagous pests in North and South America was examined in an attempt to determine the history of O. ficus-indica in the Americas. Available information suggests with some certainty t...

Ant predation on an invasive herbivore: can an extrafloral nectar-producing plant provide associational resistance to Opuntia individuals?

The legume Chamaecrista fasciculata attracts ants to its extrafloral nectar (EFN) which can lead to reduced herbivory and increased fecundity for the plant. In Florida, Opuntia stricta and O. humifusa, hosts of the invasive moth Cactoblastis cactorum, are often found growing in close association with C. fasciculata. We tested the hypotheses that O. stricta and O. humifusa individuals have higher ant abundance, lower levels of herbivore damage, and increased growth when growing in close association with C. fasciculata compared with individuals not growing near the plant. We also experimentally placed C. cactorum eggsticks and pupae on Opuntia individuals to see if ant predation of these stages occurred, and if so, whether predation rates were higher on individuals growing close to C. fasciculata. Opuntia plants near C. fasciculata were less likely to be attacked by C. cactorum and had higher ant abundance than plants far from C. fasciculata. Field surveys showed that Opuntia plants near C. fasciculata had a lower proportion of cladodes with C. cactorum damage of any type. Proportions of cladodes with damage from five native herbivores were not significantly different between treatments. In addition, Opuntia individuals growing near C. fasciculata added proportionately more pads during the growing season. We found evidence of ant predation on 15.9% of C. cactorum eggsticks and 17.6% of pupae. In August and October of 2008, there was significantly more evidence of predation on eggs and pupae placed on Opuntia individuals near C. fasciculata. No effect of distance to C. fasciculata was seen in November of 2008, potentially because plants were no longer producing EFN at this time. Our finding that Opuntia plants close to C. fasciculata show reduced herbivory from invasive C. cactorum, but not from the native herbivores examined, suggests that patterns of associational resistance may be influenced by the co-evolutionary history of the organisms in question.

Egg Parasitoids AttackingCactoblastis cactorum(Lepidoptera: Pyralidae) in North Florida

Interest in the natural enemies of Cactoblastis cactorum (Berg) has increased since the moth was found in Florida in 1989. Previous surveys for natural enemies in Argentina identified egg parasitoids in the family Trichogrammatidae as potentially important control agents of C. cactorum. A study was conducted in north Florida to identify and to assess occurrence of egg parasitoids attacking this invasive moth in its new homeland. Surveys undertaken at 6 locations in north Florida from Jul 2008 to Dec 2009 revealed that eggsticks of C. cactorum were attacked by egg parasitoids from the Trichogramma genus: T. pretiosum Riley, T. fuentesi Torre, and an additional unidentified Trichogramma species belonging to the T. pretiosum group. In order to assess the importance of these egg parasitoids, the fate of individual C. cactorum eggsticks was determined during weekly visits to each site. This assessment showed that the combined level of parasitism of C. cactorum eggsticks was very low with less than 0.2% of host eggs attacked at any one of the 6 sites. While parasitoids attacked smaller eggsticks, there was no correlation between the numbers of eggs in an eggstick attacked with increasing number of eggs/eggstick. Comparing the mean number of eggs/eggstick, there was no difference between the 3 flight periods of C. cactorum, but there was a difference between the 6 sites. Based on these results, the use of Trichogramma wasps as an inundative biological control agent, complementary to the Sterile Insect Technique application, is discussed.

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.

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 Detection of Bacillus thuringiensis in Mass Rearing of Cactoblastis cactorum (Lepidoptera: Pyralidae)

ABSTRACT A colony of the cactus moth, Cactoblastis cactorum Berg, suffered a die-off that involved 100% larval mortality in selected rearing containers. Preliminary microscope examination of wet mounts prepared from dead larvae revealed the presence of numerous uniform, highly refractive particles reminiscent of bacterial spores. Utilizing a combination of bacteriological, molecular, and chemical methods the causal agent responsible for this die-off was found to be a strain of the insecticidal Bacillus thuringiensis var. kurstaki. Significantly, larvae that were killed supported bacterial growth and sporulation. The gregarious feeding habit of this insect combined with the ability of this bacterium to amplify in dead larvae explains in part the observed rapid spread of sepsis in the rearing containers. Screening the various diet ingredients demonstrated that the cannellini bean flour harbored a variety of heat resistant bacilli including both Bacillus cereus and B. thuringiensis implicating it as the like...

Death and Decline of a Rare Cactus in Florida

Conseola corallicola is a rare cactus that is known from just two islands in Florida, Little Torch Key and Swan Key. The appearance of the cactus-eating moth, Cactoblastis cactorum, in the 1980s, threatened its survival. Outplantings at various locations were made in the 1990s and early in the 21st century to try to boost population sizes in the field and to determine optimal outplanting conditions. Here, I examine the survival of these cacti and compare it to the survival of volunteers around the bases of parent plants at Little Torch Key. I correlate percent survival in all locations with soil nutrients.Survival of recruits in outplantings was lower than that of volunteers around parent plants. Transplant experiments showed the physical act of replanting did not reduce survival. Cacti planted close to individuals of prickly pear cactus, Opuntia stricta, suffered from attack by Cactoblastis as they spilled over from O. stricta onto C. corallicola outplantings. Survival of cacti planted far away from O. stricta was often low because of poor soil quality and high mortality from crown rot. Where cacti were not killed by Cactoblastis, survival was greatest where soil nutrient content and water content were highest. Soil fertilization did not increase survival rates, but did increase survivor growth. Future restoration of C. corallicola in the Florida Keys is likely to prove difficult. As Cactoblastis spreads throughout the United States and Mexico, these same issues will likely be faced by Cactoblastis-susceptible cacti in many other locations.

Experimental test of biotic resistance to an invasive herbivore provided by potential plant mutualists

Understanding the influence of resident species on the success of invaders is a core objective in the study and management of biological invasions. We asked whether facultative food-for-protection mutualism between resident, nectar-feeding ants and extrafloral nectar-bearing plants confers biotic resistance to invasion by a specialist herbivore. Our research focused on the South American cactus-feeding moth Cactoblastis cactorum Berg (Lepidopetra: Pyralidae) in the panhandle region of Florida. This species has been widely and intentionally redistributed as a biological control agent against weedy cacti (Opuntia spp.) but arrived unintentionally in the southeast US, where it attacks native, non-target cacti and is considered a noxious invader. The acquired host-plants of C. cactorum in Florida secrete extrafloral nectar, especially on young, vegetative structures, and this attracts ants. We conducted ant-exclusion experiments over 2 years (2008 and 2009) at two sites using potted plants of two vulnerable host species (O. stricta and O. ficus-indica) to evaluate the influence of cactus-visiting ants (total of eight species) at multiple points in the moth life cycle (oviposition, egg survival, and larval survival). We found that the presence of ants often increased the mortality of lab-reared C. cactorum eggsticks (stacks of cohered eggs) and larvae that we introduced onto plants in the field, although these effects were variable across sites, years, host-plant species, ant species, and/or between old and young plant structures. In contrast to these “staged” encounters, we found that ants had little influence on the survival of cactus moths that occurred naturally at our field sites, or on moth damage and plant growth. In total, our experimental results suggest that the influence of cactus-visiting ants on C. cactorum invasion dynamics is weak and highly variable.

Field-Level Validation of a Climex Model forCactoblastis cactorum(Lepidoptera: Pyralidae) Using Estimated Larval Growth Rates

Invasive pests, such as the cactus moth, Cactoblastis cactorum (Berg) (Lepidoptera: Pyralidae), have not reached equilibrium distributions and present unique opportunities to validate models by comparing predicted distributions with eventual realized geographic ranges. A CLIMEX model was developed for C. cactorum. Model validation was attempted at the global scale by comparing worldwide distribution against known occurrence records and at the field scale by comparing CLIMEX "growth indices" against field measurements of larval growth. Globally, CLIMEX predicted limited potential distribution in North America (from the Caribbean Islands to Florida, Texas, and Mexico), Africa (South Africa and parts of the eastern coast), southern India, parts of Southeast Asia, and the northeastern coast of Australia. Actual records indicate the moth has been found in the Caribbean (Antigua, Barbuda, Montserrat Saint Kitts and Nevis, Cayman Islands, and U.S. Virgin Islands), Cuba, Bahamas, Puerto Rico, southern Africa, Kenya, Mexico, and Australia. However, the model did not predict that distribution would extend from India to the west into Pakistan. In the United States, comparison of the predicted and actual distribution patterns suggests that the moth may be close to its predicted northern range along the Atlantic coast. Parts of Texas and most of Mexico may be vulnerable to geographic range expansion of C. cactorum. Larval growth rates in the field were estimated by measuring differences in head capsules and body lengths of larval cohorts at weekly intervals. Growth indices plotted against measures of larval growth rates compared poorly when CLIMEX was run using the default historical weather data. CLIMEX predicted a single period conducive to insect development, in contrast to the three generations observed in the field. Only time and more complete records will tell whether C. cactorum will extend its geographical distribution to regions predicted by the CLIMEX model. In terms of small scale temporal predictions, this study suggests that CLIMEX indices may agree with field-specific population dynamics, provided an adequate metric for insect growth rate is used and weather data are location and time specific.

Phenology and Egg Production of the Cactus Moth (Lepidoptera: Pyralidae): Comparison of Field Census Data and Life Stage Development in the Field

Natural phenology and development of the cactus moth, Cactoblastis cactorum (Berg) (Lepidoptera: Pyralidae), was studied under field conditions in St. Marks National Wildlife Refuge, St. Marks, FL, from July 2006 to September 2007. Pads of cactus (Opuntia stricta Haw. [Cactaceae]) were visually surveyed weekly for presence of moth immature stages. Adult male C. cactorum populations were surveyed using a pheromone lure and wing style sticky traps. The field census data identified 3 generations per year which generally occurred in August to September, October to April, and May to July. Numbers of eggsticks peaked in midAugust, midOctober and midApril. High numbers of early larval immatures (1st to 3rd instars) were recorded in October 2006, May 2007 and September 2007. High numbers of late-stage larvae (4th to 5th instar) were recorded in September to October 2006, December to January 2006, June to July 2007. Peak numbers of Cactoblastis male adults occurred approximately in midOctober 2006, April to May 2007, and July to August 2007. Pupae were cryptic and difficult to sample. Development in field cages was studied by introducing cohorts of moth eggs on potted cactus plants (Opuntia ficus-indica (L.) Mill.) into the field at approximately the same times they were found to occur naturally. During the course of each generation, the potted plants were returned to the laboratory for determination of moth lifestage. Body weights and lengths also were recorded. In the field cages, 3 generations were observed and these coincided with the populations that were observed in the open field. However, the generations were more clearly defined because eggs were introduced as cohorts and most insects were recovered. Measurements of larval head capsules and body lengths show that development in the winter generation is slower than that of the summer and fall generations, although peak measurements are approximately identical in all 3 generations. Female pupae weighed 225.25 (± 4.8 SE) mg which was significantly heavier than males weighing 138.01 (± 5.5) mg. Pupal weights differed according to generation, but there was no effect on adult weight. Female adults weighed 130.3 (± 11.3) mg, compared with males, which weighed 60.81 (± 2.4) mg. Adult sex ratio was approximately 1:1. Male adults appeared to have emerged earlier than females in the fall generation.

Oviposition preference of Cactoblastis cactorum (Lepidoptera: Pyralidae) in caged choice experiments and the influence on risk assessment of F1 sterility

Releases of lepidopteran biological control agents have successfully controlled invasive weed species. However, issues with non-target effects of released exotic agents have resulted in stringent pre-release host specificity testing. Use of inherited (F1) sterility, a radiation induced genetic condition that can cause sterility in the F1 generation, could further assess the risk of non-target effects and negative ecological effects under field conditions. This technique may aid in approving potentially effective and safe biological control agents for release. The unintentional arrival of the cactus moth, Cactoblastis cactorum, into the United States provides a unique opportunity to evaluate the potential of F1 sterility. This study was conducted to assess host oviposition preferences of C. cactorum females mated with irradiated and non-irradiated males for cactus species from seven groups based on location, cactus growth characteristics (plant structure), spine densities, genera, and economic importance. No significant differences in female host preference were observed between females mated with normal or irradiated males. Lack of significant differences in oviposition preference suggests that inherited (F1) sterility has potential as a risk assessment tool for potential exotic biological control agents for invasive weed species. Evaluation of the overall analysis of female C. cactorum host preference revealed that significantly different numbers of eggsticks were oviposited on cactus species. In whole plant cages, significantly more eggsticks were oviposited on Opuntia corallicola than any other species, and in cladode cages, significantly more eggsticks were oviposited on Opuntia humifusa than all other species except Opuntia pusilla.

Flight Phenology of MaleCactoblastis cactorum(Lepidoptera: Pyralidae) at Different Latitudes in the Southeastern United States

ABSTRACT Long term trapping studies of the invasive moth Cactoblastis cactorum (Berg) were conducted at various latitudes from Puerto Rico to South Carolina. Three flight periods per year were identified at the 5 temperate sites studied, which covered the majority of the infested range on mainland United States. In general, the 3 flight periods across a latitudinal gradient from south Florida to central, coastal South Carolina were a spring flight during Feb–-May, a summer flight during Jun–Aug, and a fall flight during Sep–Nov. At any 1 site, each flight period lasted about 2 months. In the tropical areas of the Florida Keys and a Caribbean Island, the insect exhibited overlapping generations. Previous studies of this insect (as a biological control agent) report 2 flight periods per year in its native range of Argentina and its introduced range of Australia and South Africa. A synthetic pheromone-baited trap was a good indicator of generational time, and we suggest that trapping assays in these areas wi...