Screwworm eradication program in Central America

Morphological and Molecular Characterizations of Cochliomyia hominivorax (Diptera: Calliphoridae) Larvae Responsible for Wound Myiasis in French Guiana

Myiasis is an ectoparasitic infection caused by the larvae of true flies (Diptera). We came across a rather rare case of myiasis in an immunocompetent 34-year-old man from French Guiana with advanced wound myiasis masquerading as cavitary myiasis and a history of cholesteatoma surgery in the left ear. The Diptera larvae responsible for the disease were isolated and identified using morphological and molecular approaches as Cochliomyia hominivorax. We underline the importance of this parasitosis as the second case of myiasis caused by C. hominivorax and the first case of wound myiasis in this overseas department of France and its incidence in pre-urban areas of the capital, Cayenne, in South America.

The Sterile Insect Technique: Success and Perspectives in the Neotropics

The sterile insect technique (SIT), an environmentally friendly means of control, is currently used against plant, animal, and human pests under the area-wide integrated pest management. It consists in the mass production, sterilization, and release of insects in an affected area where sterile males mate with wild females leading to no reproduction. Here, we review SIT in the Neotropics and focus on particular recent successful cases of eradication of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann), as well as effective programs used against the Mexican fruit fly Anastrepha ludens (Loew), the New World screwworm fly Cochliomyia hominivorax (Coquerel)), and the Cactus moth Cactoblastis cactorum (Berg). We examine when SIT does not work and innovations that have made SIT more efficient and also highlight complimentary techniques that can be used in conjunction. We address potential candidate species that could be controlled through SIT, for example Philornis downsi Dodge & Aitken. Finally, we consider the impact of climate change in the context of the use of the SIT against these pests. Given the recent dramatic decline in insect biodiversity, investing in environmentally friendly means of pest control should be a priority. We conclude that SIT should be promoted in the region, and leadership and political will is needed for continued success of SIT in the Neotropics.

Proteolytic activity of excretory/secretory products of Cochliomyia hominivorax larvae (Diptera: Calliphoridae)

Abstract: The protein profiles and proteolytic activity of the excretory secretory products (E/SP) of the first (L1), second (L2) and third (L3) larval stages of Cochliomyia hominivorax were studied in the laboratory. Analysis on the E/SP protein profile was carried out using polyacrylamide gel containing sodium dodecyl sulfate (SDS-PAGE). The E/SP of each larval stage (L1, L2 and L3) treated with protease inhibitors, containing 30μg, 40μg and 50μg of protein, was applied to the 10% polyacrylamide gel. The proteolytic activity of the crude E/SP was analyzed in gels copolymerized with gelatin and by colorimetric assays using azocasein as a substrate, with the characterization of the proteases using synthetic inhibitors. Different protein profiles were observed for the larval instars, with L1 presenting the most complex profile. Nevertheless, various protein bands were observed that were common to all the larval instars. The E/SP of all the instars showed proteolytic activity on gelatin, evidenced by proteolysis zones, predominantly with apparently higher molecular masses in L1, while for L2 and L3 the proteolysis zones could also be observed in regions with lower masses. Tests with protease inhibitors using gelatin as substrate showed that the E/SP of larvae were mainly composed of serine proteases. Additionally, inhibition was observed in L2 E/SP treated previously with EDTA, an inhibitor of metalloproteases. The assays with azocasein revealed a gradual increase of proteolytic activity on this substrate with larval development progress, with the strongest inhibitions being observed after treatments with 3,4-dichloroisocoumarin (DCI) for E/SP of L1, L2 and L3. These results suggest that C. hominivorax larvae produce different proteases, a fact that can be related to the parasite's vital processes for survival, such as penetration into the host's tissues and nutrition during the larval stage.

Sequence-characterized amplified regions that differentiate New World screwworms from other potential wound-inhabiting flies

New World screwworms, Cochliomyia hominivorax (Coquerel, 1858), were once devastating pests of warm-blooded animals in the United States before they were successfully eradicated using the sterile insect technique. Guarding against the introduction of screwworms to North America or any other screwworm-free area relies on rapid, reliable identification of suspected cases. In the current study, the DNA from excised markers generated by randomly amplified polymorphic DNA polymerase chain reaction was used as the basis to generate 2 species-specific sequence-characterized amplified region molecular markers. Resulting primer pairs, named CR92A1 and J1A2 (each with forward and reverse components), produced amplicons of 852 and 848 base pairs, respectively. The 2 primer pairs successfully discriminated between C. hominivorax, Cochliomyia macellaria (Fabricius, 1775), 8 other species of blowflies, 3 noncalliphorid dipterans, and 1 nondipteran outlier. These primers may become important tools for veterinary laboratories and the screwworm eradication and exclusion program for rapid identification or verification of suspicious larval samples in presumed outbreaks.

African trypanosomiasis

Trypanosomiasis remains one of the most serious constraints to economic development in sub-Saharan Africa and, as a consequence, related research has been subject to strong social and political as well as scientific influences. The epidemics of sleeping sickness that occurred at the turn of the 20th Century focussed research efforts on what became known as 'the colonial disease'. This focus is thought to have produced 'vertical' health services aimed at this one disease, while neglecting other important health issues. Given the scale of these epidemics, and the fact that the disease is fatal if left untreated, it is unsurprising that sleeping sickness dominated colonial medicine. Indeed, recent evidence indicates that, if anything, the colonial authorities greatly under-estimated the mortality attributable to sleeping sickness. Differences in approach to disease control between Francophone and Anglophone Africa, which in the past have been considered ideological, on examination prove to be logical, reflecting the underlying epidemiological divergence of East and West Africa. These epidemiological differences are ancient in origin, pre-dating the colonial period, and continue to the present day. Recent research has produced control solutions, for the African trypanosomiases of humans and livestock, that are effective, affordable and sustainable by small-holder farmers. Whether these simple solutions are allowed to fulfil their promise and become fully integrated into agricultural practice remains to be seen. After more than 100 years of effort, trypanosomiasis control remains a controversial topic, subject to the tides of fashion and politics.

Acetylcholinesterase cDNA sequencing and identification of mutations associated with organophosphate resistance in Cochliomyia hominivorax (Diptera: Calliphoridae)

Altered acetylcholinesterase (AChE) has been identified in numerous arthropod species resistant to organophosphate (OP) and carbamate insecticides. The New World screwworm (NWS) Cochliomyia hominivorax (Coquerel), one of the most important myiasis-causing flies in the Neotropics, has been controlled mainly by the application of OP insecticides in its current geographical distribution. However, few studies have investigated insecticide resistance in this species. Based on previous studies about mutations conferring OP resistance in related dipteran species, AChE cDNA was sequenced allowing a survey for mutations (I298V, G401A, F466Y) in NWS populations. In addition, the G137D mutation in the carboxylesterase E3 gene, also associated with OP resistance, was analyzed in the same NWS populations. Only 2/135 individuals presented an altered AChE gene (F466Y). In contrast, a high frequency of the G137D mutation in the E3 gene was found in some localities of Brazil and Uruguay, while the mutant allele was not found in Cuba, Venezuela or Colombia. These findings suggest that the alteration in the carboxylesterase E3 gene may be one of the main resistance mechanisms selected in this ectoparasite. The knowledge of the frequency of these resistance-associated mutations in the NWS natural populations may contribute to the selection of appropriate chemicals for control as part of pest management strategies.

Candidate sex pheromones of the New World screwworm Cochliomyia hominivorax

Five novel homologous acetate derivatives of long-chain secondary alcohols and a related ketone were tested for their efficacy as contact mating stimulants for Cochliomyia hominivorax Coquerel (Diptera: Calliphoridae). Full copulatory behaviour at a high percentage was found in tests with racemic 6-acetoxy-19-methylnonacosane at 2.5-20 microg using fertile males from three strains. Males of two strains responded nearly as well to 7-acetoxy-15-methylnonacosane, but an older strain first colonized in 1992 did not respond to this compound. Few or no copulatory responses were obtained to the other secondary alcohol acetates and a related ketone. These two acetate derivatives are the first sex pheromones identified in a calliphorid fly. The threshold of response was also tested, but could not be pinpointed.

Antennal sensilla of the New World screwworm fly, Cochliomyia hominivorax (Diptera: Calliphoridae)

Antennal sensilla of the Cochliomyia hominivorax were studied by scanning electron microscopy. Thirteen subtypes of sensilla were identified in the fly antenna. In the antennal funiculus, nine subtypes were found: one trichoid, three basiconic, and five coeloconic. Among these, olfactory sensilla were morphologically recognized. Long bristle sensilla presenting various sizes and distribution patterns were observed in the scape and pedicel. In this segment, two other types of tricoid sensilla were still observed. The three antennal segments were shown to be coved by smaller spinules of the microtrichia type. No type of sensillum was seen in the aristas of C. hominivorax. Consistent differences between the sexes in typology, topography, and quantity of antennal sensilla were verified. The great variety of sensillary subtypes, presenting wall pores and/or grooves, found in the funiculus of C. hominivorax, indicates the olfaction should play an important role in this species behavior and communication. The data of the current study, besides corroborating in the amplification of the morphologic and ultrastructural knowledge of C. hominivorax, can foment future electrophysiological studies for the development of volatile semiochemicals, to be uses as attractants in traps, as a new alternative to monitoring and/or controlling this fly.

An initial survey of the cattle grub Dermatobia hominis (L. Jr.) in Nicaragua

After the civil war and the Hurricane-Mitch disaster, cattlemen in Nicaragua were forced to transport their cattle from lowland areas to higher, dryer areas of the country. These areas are natural ecological niches for the cattle grub Dermatobia hominis (L. Jr.) (Diptera: Cuterebridae). To determine the importance of this infestation, the Agricultural and Livestock-Forestry Ministry selected a central area of Nicaragua to run a pioneer survey program to acquire information about hosts involved, number of cases, treatments applied and general knowledge of 42 farmers about the life cycle of the parasite. The subjects were either farm owners or farm managers. Ninety-five percentage of the farms indicated cases of D. hominis infestation in their animals, with cattle being the most affected host (100% of the affected farms). There was poor understanding of the D. hominis life cycle, vectors and control methods. A misuse of insecticides for the treatment of larval infestation by D. hominis was indicated.

Identification of screwworms, Cochliomyia hominivorax (Coquerel) (Diptera: Calliphoridae), with a monoclonal antibody-based enzyme-linked immunosorbent assay (MAb-ELISA)

Myiasis caused by screwworms, Cochliomyia hominivorax (Coquerel), is devastating to warm-blooded animals and economically important to livestock producers. It is difficult to distinguish these pests, immature screwworms, from immatures of other non-pest fly species that often occur in animal wounds; it would be helpful to have tools available that do not rely on morphological characteristics. We developed two monoclonal antibodies (MAbs), highly specific for the screwworm, and used them in an enzyme-linked immunosorbent assay (MAb-ELISA), that differentiated screwworm eggs, larvae, pupae, and adults from those of the closely related secondary screwworm, C. macellaria (Fabricius) as well as Phormia regina (Meigen), Phaenicia sericata (Meigen), Calliphora vicina Robineau-Desvoidy, and Chrysomya rufifacies (Macquart). In a blind study, the microplate MAb-ELISA, which took about 4h to complete, displayed high specificity (99%), sensitivity (92%) and overall accuracy (97%) in distinguishing all life stages of the screwworm. Electrophoresis results suggested that the two monoclonal antibodies recognized identical conformational epitopes present in all screwworm life stages. The screwworm eradication program, successful in eradicating this pest from the US, Mexico, most of Central America and Libya (after an accidental introduction), could benefit in future eradication, surveillance, and exclusion efforts by developing a reliable field identification kit based on MAb-ELISA that accurately and quickly distinguished cases of screwworm myiasis.

Permeabilization of Cochliomyia hominivorax (Diptera: Calliphoridae) embryos

Embryos of the primary screwworm, Cochliomyia hominivorax (Coquerel), were successfully permeabilized for use in subsequent cryopreservation studies. Mortality was greater for eggs incubated for < 5 h before treatment. The mean survival of embryos to first instars was 55.7, 61.1, and 62.6% when the embryos were incubated for 5, 5.5, and 6 h before treatment, respectively. The survival to the pupal and adult stages was low. An improved media for culturing the embryos during and immediately after treatment needs to be devised and the procedure for rearing the larval stages also needs to be altered to improve survival for emerging adults.

Eradication revisited: dealing with exotic species

Invasions of nonindigenous species threaten native biodiversity, ecosystem functioning, animal and plant health, and human economies. The best solution is to prevent the introduction of exotic organisms but, once introduced, eradication might be feasible. The potential ecological and social ramifications of eradication projects make them controversial; however, these programs provide unique opportunities for experimental ecological studies. Deciding whether to attempt eradication is not simple and alternative approaches might be preferable in some situations.

Entomology in the twentieth century

A number of landmark events in applied entomology are listed together with some insect-related studies that have had a major impact on biology in general. In large part, however, advances in our understanding of insects have depended on technological advances, especially in the second half of the century. The exponential increase in the ease and extent of communication has been critical. Sometimes, as in the field of insect/plant relations, the ideas of a few individuals have been critical with technological advances having a facilitating role. Elsewhere, as in the study of olfaction, major changes in understanding have been directly dependent on new technology. Very brief accounts of the impacts on insect-related science of developments in the fields of radio, radioactivity, immunology, imaging techniques, and chemical analysis are given. Despite the importance of technology, the lovers of their insects continue to have a key role.

Persistent activity of doramectin and ivermectin in the prevention of cutaneous myiasis in cattle experimentally infested with Cochliomyia hominivorax

A study was conducted to evaluate the activity of a single administration of doramectin or ivermectin against severe, induced infestations of Cochliomyia hominivorax. Twenty-four Holstein bull calves were allocated to four groups of six animals each and treated either with saline, doramectin 1%, or either one of two formulations of ivermectin 1% at a dose rate of 200 microg/kg. On Day 12 after treatment, each calf was anesthetized and two wounds were created on the left side of the shoulder and rump of each calf and 2 h later, each wound was implanted with 100 newly hatched larvae of C. hominivorax. On Day 15 after treatment, the procedure was repeated on the right side of each calf. Wounds were examined daily for 5 days and evidence of live larvae was recorded. Doramectin provided reduction in myiasis of 90.9 and 83.3% at 12 and 15 days after treatment, respectively, compared to the saline control treatment (P < 0.0001). In contrast, there were no significant differences in the number of calves with myiasis between those treated with either of the ivermectin formulations and the saline control.

Eradication and pest management

Eradication is the elimination of every single individual of a species from an area to which recolonization is unlikely to occur. Cost-benefit analyses of eradication programs involve biases that tend to underestimate the costs and overestimate the benefits. In this review, we (a) highlight limitations of current cost-benefit analyses, (b) assess eradication strategies from biological and sociological perspectives by discussing particular cases of successful and failed eradication efforts, and (c) briefly contrast eradication and ongoing area-wide control as pest management strategies. Two successful eradication programs involve the screwworm and cattle ticks. Gypsy moth and medfly eradication programs have not been successful, and subsequent captures of insects recur in eradication areas. In situations where heterogeneity of land use patterns make it difficult to prevent reinvasion of the pest, education and area-wide suppression are probably more realistic goals than eradication.