Summary
The feedlot industry has applied a significant amount of effort to improved manure management practices over the past decade as a means of reducing odour emissions and fly problems. There is, however, evidence that fly populations remain a serious problem. Insecticide resistance and a desire to minimise the use of chemicals also drive the need to move to a more integrated approach to fly control. A questionnaire survey of Australian feedlots on fly control showed that 83% of feedlot operators considered flies a problem and that working conditions, human health, animal welfare, chemical residues and production losses were rated as the most important adverse impact of flies.
The survey indicated that flies are controlled by a range of physical, cultural and chemical means. Almost 60% of the feedlots used some form of chemical fly control. Forty-three percent of respondents used baits, about a quarter used insecticide sprays, and 15% used traps to control flies. The effectiveness of these treatments was considered to be moderate by the majority of the respondents. The data collected in this survey was used to finetune the feedlot fly and parasite monitoring programs, select commonly used chemicals for resistance testing and formulate integrated pest management guidelines for the control of fly populations. Good control from insecticides relies on knowing what resistance is present in the fly populations and using the remaining effective chemicals in carefully planned programs. Flies from southern Queensland (SQ) showed a moderate level of resistance to diazinon (19 x), a lower level to trichlorfon (3.2 x) and were susceptible to azamethiphos and cyfluthrin. The central New South Wales (CNSW) and central Queensland (CQ) isolates showed moderate levels of resistance to diazinon (7 to 11 x), and appeared susceptible to azamethiphos and cyfluthrin. All feedlot isolates showed a reduced mortality response to Snip Fly Bait and the SQ and CNSW flies also showed a reduced mortality to Dy-Fly bait but not to the same extent as with Snip. The observed reduction in bait efficacy was due to a change in the flies behaviour. The impact on field efficacy of these baits is uncertain, although some loss of control might be expected. Populations of adult and immature nuisance flies and their parasites were monitored on three Australian feedlots with one SQ feedlot being continuously monitored over two years. The most commonly trapped adult flies on the SQ feedlot were house flies (Musca domestica, 38% of total fly catch) and hairy maggot blowflies (Chrysomya rufifacies, 27%). Other common species trapped were the bush fly (M. vetustissima, 15%) and the stable fly (Stomoxys calcitrans, 1.3%). All fly populations were low during the coldest winter months, house flies had one broad annual population peak extending over nine months, whereas stable flies showed two peaks in late autumn and late spring. House fly and stable fly populations were higher inside than outside the feedlot, whereas bush fly and blowfly catches were generally higher outside the feedlot. There was a strong correlation between the number of adult flies and behavioural responses of cattle irritated by flies. The frequency of tail swishes, ear flicks and head tosses can be used to gauge house fly and bush fly populations, and leg stomps correlated well with the stable fly populations. Systematic counts of the frequency of these movements can provide an estimate of prevailing fly populations. Of the major fly species trapped on the feedlot, only house flies (86% of feedlot larvae) and stable flies (10%) breed on the feedlot, whereas all others predominantly breed outside the feedlot. The highest numbers of larvae were found where a mixture of manure, vegetation and moisture was present. The hospital/induction area, under the pen fence lines, drains and silage pits all provide such ideal substrates for fly development. Fly breeding is concentrated in relatively small pockets in the feedlot.
A strategy for reducing fly breeding in the cattle feedlot would involve a more targeted and more frequent cleaning of these major fly breeding areas. Manure scraping and removal from cattle pens and fence lines was generally performed on a routine basis at two to three month intervals. The subsequent reduction in adult or immature fly populations was short-lived. The build up of non-compacted manure under the fences occurred rapidly after cleaning, and fly breeding quickly returned to its previous level. Insecticidal treatments were infrequent and generally applied when there was a perceived need rather than on a routine basis. Fly baits, which attract and kill adult house flies only, were also used when deemed necessary. The insecticidal treatments had little if any impact on fly breeding or fly populations on the feedlot. Biological control agents, including parasitic wasps, predatory mites and entomopathogenic fungi play an important role in lowering feedlot fly populations. Eight species of parasitic wasps, mainly Spalangia spp., were found on the SQ feedlot where they killed at least 27% of the developing flies. The parasitic wasps detected on the feedlot are also found in America and Europe, where they are commercially cultured for the control of flies in intensive livestock industries. The presence of these wasps provides Australian feedlot managers with the opportunity to use parasitic wasps for biological control of nuisance flies. In the SQ feedlot the average level of mite infestation was 3.8% and 3.2% for house and stable flies respectively. The contribution of the various mites in the biocontrol of fly populations associated with livestock has not been generally established. Fungi from a few selected entomopathogenic genera were isolated from feedlot flies and were highly effective in killing house flies, making them potential candidates for the development of a fungal biopesticide for flies. Integrated pest management (IPM) systems embrace the integration of cultural (mechanical/physical), biological and chemical control methods to reduce pest populations.
IPM strategies need to be tailored for particular situations, incorporating all available approaches and reducing insecticide use. The RULES for an integrated pest management approach for nuisance flies on cattle feedlots, are presented below:
Reducing fly breeding sites
Manure management (under fence lines, sedimentation ponds, drains, hospital area, stock piles)
Spilled feed (feed bunks, hospital area, stables, feed processing area)
Silage (spills, cover pits completely)
Carcases (compost, cover completely)
Feedlot maintenance (troughs, drains, sedimentation ponds, vegetation)
Using insecticides selectively
Rotate chemical groups
Targeted insecticide use (hot spots)
Adulticides (residual rather than knockdown insecticide; spray resting sites not manure)
Larvicides (use an insect growth regulator (IGR) which do not affect beneficial insects)
Baits (use for house flies only and rotate between chemical groups) Lot feeding design principles
Appropriate pen foundation and optimal slope
Feed and water trough design
Fence design to allow for easy cleaning
Construction of drains, sedimentation systems and effluent holding ponds
Manure stockpile and composting area Enhancing populations of biological control agents
Biological control agents play an important role in fly control
Preserve parasite and predator populations through appropriate management
Augment parasite populations through strategic releases Systematic monitoring of fly populations
Scouting (adults and larvae; to determine population thresholds)
Traps for adults; larval density ratings for immatures
Animal observations It is recommended that:
1. Feedlot operators design and implement an integrated pest management (IPM) program for nuisance flies on their feedlot, incorporating the RULES given above.
2. MLA, DPI&F and ALFA jointly produce guidelines based on these RULES to assist feedlot operators in the design and implementation of IPM programs for nuisance flies on cattle feedlots.:
3. Further R&D on nuisance flies in cattle feedlots be carried out, to develop and use parasitic wasps and entomopathogenic fungi for biological fly control and to determine how to optimally combine these tools with feedlot design and management to provide effective fly control with minimal use of insecticides.
