Cochliomyia Research Articles

The effect of the bont tick (Amblyomma hebraeum) on the weight gain of Africander steers.

The effects of the bont tick Amblyomma hebraeum on the productivity of cattle need to be quantified in order to design economically optimal control programs. Liveweight gains (LWGs) of three groups of Africander steers, maintained in the same pasture and exposed to zero, medium or high numbers of larvae, nymphs and adults of the tick, were measured. Larvae and nymphs had no significant effect on LWG but adults had a large, statistically significant effect (P less than 0.05). The tick-free group had an average LWG of 20 kg more than the heavily infested group after 3.5 months. No mortality was recorded from ticks or tick-borne diseases during the experiment. There was no relationship between the number of engorging adult female ticks counted and loss of LWG of individual animals. The latter suggests that exposure to ticks as well as engorgement by female ticks causes losses. The loss per adult female that completed engorgement was estimated, by relating the LWGs of individual animals to their tick infestations, to be 4 +/- 2 g per adult female tick. An alternative estimate, made by comparing the average LWG and tick infestations of each treatment group, was equal to 10 +/- 4 g. This latter estimate includes the effect of challenge (and rejection) as well as tick feeding and so was accepted as giving the best estimate. Screw-worm fly (Chrysomya bezziana) struck an average of 7.5% of the cattle infested with ticks in any week but the effects on the productivity of the cattle were minimized by immediate treatment. There was a significant, positive correlation between the incidence of screw-worm fly strike and the numbers of adult ticks counted on the experimental animals. The results provide data for calculating losses caused by A. hebraeum in different parts of its geographical range.

The screwworm fly in Libya: a threat to the livestock industry of the Old World.

The screwworm fly, Cochliomyia hominivorax (Coquerel), is the most serious insect pest of cattle in the New World. It has recently been recorded in Libya, where it appears to have become established. This article documents these recent finds, and provides background information on the recognition of the fly, its biology, distribution and importance.

The potential geographical distribution of the Old World screw‐worm fly, Chrysomya bezziana

The potential geographical distribution and relative abundance of the Old World screw-worm fly, Chrysomya bezziana Villeneuve (Diptera: Calliphoridae) as determined by climate, was assessed using CLIMEX, a computer program for matching climates. CLIMEX describes the relative growth and persistence of animal populations in relation to climate. The observed global distribution of C.bezziana was compared with the potential distribution predicted by CLIMEX. The differences in the two distributions indicate the areas at risk of colonization, with particular reference to Australia and the Americas. According to the model, the potential area of permanent colonization in Australia extends south to the mid-coast of New South Wales. Comparison of areas suitable for permanent establishment with the potential summer distribution indicates that large additional areas, carrying most of the continent's livestock, could be colonized in the summer months. Seasonal population growth indices are presented for three ports in Australia at which screw-worm fly specimens have been collected by quarantine authorities. They indicate the relative risk associated with introductions at different places in different seasons and so provide valuable planning information for quarantine authorities. The CLIMEX predictions for C.bezziana in North America are shown to be similar to the recorded distribution limits of the New World screw-worm fly, Cochliomyia hominivorax (Coquerel). The fly could also colonize South America, as far south as southern Brazil and midway through Argentina.

Oviposition and Wound-Visiting Behavior of the Screwworm Fly, Cochliomyia hominivorax (Diptera: Calliphoridae)

Female screwworm flies, Cochliomyia hominivorax (Coquerel), visit wounds of warm-blooded animals to feed and oviposit, with feeding visits occurring twice as often as oviposition visits. Feeding visits average 5.4 min and oviposition visits average 15.4 min, but both types of visit may last up to 1 h. Screwworms are iteroparous, with oviposition occurring in a 3-d cycle. One female fly was recorded to live 33 d and oviposited at least eight times. Oviposition activity by the population followed a 17–19-d cycle, which probably corresponds to the life cycle of the fly. Clutch size is variable from 28–492 eggs, with a mean of 200 eggs per clutch. Females deposit their clutch in one to four masses of eggs, usually on the margin of a wound. If a wound is preoccupied by an egg mass, an ovipositing female places her egg mass on top of or in direct contact with the previous egg mass most (67%) of the time. Thus, the presumption of one egg mass equalling the reproductive output of a single female is invalid. Female screwworms combine longevity and iteroparity with autogeny and large clutches. This reproductive behavior is well adapted for exploitation of a transitory resource such as wounds on living animals.

The influence of seasonal temperatures on the natural regulation of the screw worm, Cochliomyia hominivorax, in the southern U.S.A.

The incidence of screwworm cases in Texas during the 1962-82 sterile-male eradication campaign is analysed in relation to seasonal temperatures and screwworm density. The analysis shows that screwworm outbreaks occur in response to favourable seasonal conditions, especially warm winters and cool summers. The outbreaks collapse following cold winters and hot summers. Screwworm density in autumn also influences rates of increase, possibly through a shortage of wounded hosts in the autumn-winter period. The analysis provides a simple predictive model which not only accounts for the fluctuations in case incidence seen in Texas during the eradication campaign, which others have attributed to strain problems and release methods, but also simulates the historical pattern of screwworm abundance in both Texas and Florida over the last 100 years. It is concluded that screwworm, being essentially a tropical species, might well have been eradicated from the southern U.S.A. by exceptionally unfavourable climate such as occurred in Florida in 1958 and in Texas in the late 1970s and early 1980s. Certainly, unfavourable climate must have been important to the success of the eradication campaigns.

Occurrence of the Old World screw-worm fly Chrysomya bezziana on livestock vessels and commercial aircraft.

Occurrence of the Old World screw-worm fly Chrysomya bezziana on livestock vessels and commercial aircraft.

Biological control of insect pests affecting man and animals in the tropics.

Biological control of pests affecting the health of man and animals is practiced in various forms throughout the tropics. In this paper, the use of parasitic viruses, bacteria, protozoa, predatory arthropods, and fish against pests such as various mosquitoes, tse tse flies, and screwworm flies as published in the literature are reviewed. Mention is also made of the usefulness and applicability of the sterile insect technique, genetic control by chromosomal aberrations, and the exploitation of various incompatabilities. These are reviewed against the background of the present state of technology and limited resources that exist in many tropical countries. Most authors maintain that due to the relative length of time required to get a biological control system working efficiently, and the perennial nature of most tropical pest species, there is often the need to initially reduce the pest population by conventional means. There will thus be a balance between biological and chemical control in most systems. Emphasis is placed on meeting the urgent need for the exchange of research and development information on biological control of pests affecting man and his animals in the tropics.

Multicomponent attractant for female screwworm flies,Cochliomyia hominivorax, in bovine blood

An olfactometer bioassay was used to follow attractant for screwworm flies,Cochliomyia hominivorax, in steam distillates of bovine blood under different distillation and storage conditions and after HPLC separation of components in a water-methanol gradient. In addition, fly responsiveness was examined in relation to sex and ovarian stage. Gravid and vitellogenic nullipars were attracted to the blood, although the former predominated four to one. Males did not respond at a dose that attracted 76% of gravid females. Maximum attractiveness occurred when distillate was stored in sealed glass ampoules. An argon atmosphere made storage at ambient temperatures feasible, but offered no advantage during storage at ca. -60°C or during distillation. The HPLC separation produced four fractions that duplicated the attractiveness of the distillate when recombined but showed little activity when presented as two-fraction, and most three-fraction, mixtures. Availability of the HPLC fractions for combination with other samples will facilitate location via bioassay of attractant components in samples obtained from subsequent or alternate isolations that preserve only one or two elements of the multicomponent mixture.

The effect of the brown ear-tick Rhipicephalus appendiculatus on the growth of Sanga and European breed cattle.

The effects of larvae, nymphs and adults of the brown ear-tick Rhipicephalus appendiculatus on the growth of Bos indicus X B. taurus (Sanga) steers and on B. taurus steers and heifers was measured by exposing groups, maintained in the same pastures, to different levels of tick challenge. Larvae and nymphs had no significant effect on liveweight gains, but adults had a large effect. Each engorging female tick counted was associated with a loss of 4 g. Their effect on the Sanga cattle was minimised by host resistance which severely limited the number of ticks feeding on them. The B. taurus animals were severely affected and suffered extensive ear damage. Both breeds were subjected to screw-worm fly (Chrysomya bezziana) strike in the lesions caused by heavy tick infestations, but the B. taurus animals were much more prone to attack. The results provide a basis for calculating losses in production caused by this species of tick which is widespread in Africa.

Mitochondrial DNA variation among geographical populations of the screwworm fly, Cochliomyia hominivorax.

Levels of mitochondrial DNA (mtDNA) sequence divergence among different geographic populations of the primary screwworm fly, Cochliomyia hominivorax , were compared. Six different lines originating from the United States, Mexico, or Jamaica were analyzed using 15 different restriction endonucleases. The fraction of fragments in common ( F ) between pairs ranged from 0.69 to 0.98 ($\bar F$ = 0.87), while the estimated nucleotide sequence divergence ( p ) ranged from 0.1 to 2.7% ($\bar p$ = 1.1%). The greatest differences observed were between the Jamaican line and the mainland lines ($\bar p$ = 2.5%).

Larval and pupal weight relationships of six strains of screwworm (Diptera: Calliphoridae) reared in the laboratory and in wounds.

Relationships were determined between larval and pupal weight of the primary screwworm, Cochliomyia hominivorax (Coquerel), reared in the laboratory on an artificial diet and in animal wounds. Six strains were studied, 083, Micholima, A82, V81, Sinaloa, and 009 in colony for 5–183 generations. Linear regression analyses of larval and pupal weight showed the 083 and A82 strains reared in the laboratory to be significantly different from each other and the other strains tested. This difference could not be attributed to length of time in colony or to geographic origin of the strains. There was no significant difference in the relationship between larval and pupal weights for the six strains of screwworms reared in wounds. Composite regression lines for laboratory and wound-reared larvae and pupae were not significantly different. Mean weight loss from larva to pupa was 21 and 23% for wound and laboratory-reared screwworms. Survival from larva to adult was 91 and 94% for those reared in the laboratory and in wounds, respectively.

Habitat and mate selection in Hawaiian Drosophila.

Phyletically packed communities were studied earlier in HawaiianDrosophila and then found in a serious insect pest, the screwworm (Cochliomyia hominivorax). In this case the autocidal control effort was stalled until the community complexity was recognized and similar complexity was incorporated into the sterile flies that were released. This paper summarizes a theoretical extension of this theme. Coevolution results from feedback from the habitat to the mating system. It is predicted that a stable community may bedynamically maintained when the coevolutionary forces are somewhat relaxed and hybrids are possible between closely related gamodemes. Relaxation could result from disturbances to the habitat, colonizing a habitat not fully packed, or extinction of some members of the community of related populations. One of these conditions is similar to that discussed by Carson in the “founder-flush” mode of speciation associated with colonization of new islands by highly heterozygous individuals. Another is similar to achieving interspecific hybrids in laboratory, or other unusual, environments. And, finally, one is similar to the progressive removal of the complex of species of a “pest” by an autocidal procedure such as by releasing sterile screwworm flies.

Reproductive Factors Affecting Responses of the Screwworm Fly, Cochliomyia hominivorax (Diptera: Calliphoridae), to an Attractant of Bacterial Origin

Attraction of screwworm flies, Cochliomyia hominivorax (Coquerel), to steam distillate of culture medium inoculated with the bacterium, Providencia rettgeri (Hadley, Elkins, and Caldwell), was studied in laboratory olfactometer assays conducted with 0- to 12-d-old males and nulliparous females. Males, and females with previtellogenic ovaries, were not attracted. Those with vitellogenic ovaries demonstrated only a trace response. Females became gravid as early as 4-5 d, but the percentage of gravid females attracted increased linearly with age up to 10 d. Insemination significantly enhanced responsiveness without affecting the rate of ovarian development. Gravid mated females 10-12 d old were the most strongly attracted. The results were consistent with the hypothesis that bacterial metabolites contribute to the attractiveness of wounds on screwworm host animals.

Chemical basis for asymmetric mating isolation between strains of screwworm fly,Cochliomyia hominivorax

Laboratory mating tests and bioassays for a contact, mating-stimulant pheromone were conducted within and between two strains of the screwworm fly,Cochliomyia hominivorax. No strain or sex difference in pheromone activity occurred at emergence. However, the pheromone activity of females increased with age in one strain but declined in the other. Activity also declined in males of both strains but more steeply than in the females. Thus, sexual dimorphism in pheromone activity developed with age in both strains but to differing degrees. The decline in female pheromone activity was partly compensated for within that strain by a higher male responsiveness to pheromone. Female pheromone activity and mating success were positively correlated. Virgin females and those inseminated 24-48 hr previously were equally stimulatory. It appears that the strain differences arose from selection for reduced pheromone activity during laboratory colonization.

Use of insecticides to control screw‐worm fly strike by Chrysomya bezziana in cattle

Some insecticides to control and prevent screw-worm fly strike by Chrysomya bezziana in calves and adult cattle were tested in field trials on cattle in Sabah, East Malaysia. Ivermectin injected subcutaneously in newborn calves at 200 mu/kg provided 10 days protection from screw-worm fly strike, which allowed navels to dry. Ivermectin, 1% dichlofenthion plus gentian violet and 3% lindane plus pine oil smear were all effective in preventing re-strike of treated wounds in adult cattle. A single subcutaneous injection of ivermectin at 200 mu/kg was effective, whereas it was necessary to re-apply the dichlofenthion and lindane smear preparations every 48h.

Genetics of the screwworm fly

Three spontaneous eye mutants of Cochllomyla hominivorax, the screwworm fly are described and characterized. The mutants, yellow eye (ye), orange eye (or), and white eye (wh), segregate independently and are recessive. Yellow eye is recessively epistatic to orange eye and dominantly epistatic to white eye. All three mutants have complete penetrance, are autosomal, and have little effect on fly viability under laboratory conditions.

Polytene chromosomes, karyotype correlations, and population cytology of the primary screwworm fly

Polytene chromosomes, karyotype correlations, and population cytology of the primary screwworm fly

Orbital Myiasis

Invasion of the orbit by dipterous fly larvae is a rarely reported form of myiasis. We present a 65-year-old man with orbital myiasis caused by the tissue obligatory larvae of the Old World screw-worm fly Chrysomyia bezziana Villeneuve. Larvae were found invading the orbital apex and exenteration was carried out to prevent intracranial invasion. In this case of orbital myiasis, CT scanning was used to document the extent of intraorbital invasion. To our knowledge, this is the first reported case of ophthalmomyiasis caused by C. bezziana.

Pheromone-mediated copulatory responses of the screwworm fly,Cochliomyia hominivorax

A bioassay based on male copulatory responses occurring on contact with dead decoy insects was used to confirm the existence of a sex pheromone in the screwworm fly,Cochliomyia hominivorax. Males responded to female but not male decoys. Mated and virgin females were equally stimulatory. Activity was abolished when females were washed with hexane but partially restored by treatment with crude hexane extract of females. Responses decreased when extracts were diluted and when the number of females extracted per milliliter of hexane was decreased from 20 to 1 in the preparation of extracts concentrated to 0.4 female/μl. Sexually mature female decoys of the 009 strain, the most laboratory-adapted of three strains examined in intrastrain tests, produced few copulatory attempts compared with those of Aricruz or DE-9 strains. However, newly emerged 009 as well as Aricruz females elicited responses from about 80% of sexually mature males. Those of the DE-9 strain stimulated fewer than 1%. The observation that 009 females were maximally stimulatory before becoming receptive to mating suggests that these strain differences resulted from laboratory colonization.

Inhalant allergy following occupational exposure to blowflies

An allergic reaction, provoked by exposure to the blowfly Lucilia cuprina and shown to be IgE-mediated, occurred in a subject employed in an entomological research laboratory. The subject's serum, and sera from three other asthmatic patients with IgE antibodies to blowfly extracts, also reacted with extracts from the screw-worm fly (Chrysomya bezziana). Results suggested that antigens from the two species share immunological cross-reactivity. Cross-reactions also exist between the different developmental stages of both species. Allergic reactions to inhaled insect allergens may not be uncommon in the Australian community.