Field trials of fatty acids and geraniol applied to cattle for suppression of horn flies, Haematobia irritans (Diptera: Muscidae), with observations on fly defensive behaviors.

Adult horn fly populations were tracked on cattle for 2-week periods before, during and after multiple treatments (every 3-4days) with two repellents in a mineral oil carrier. Cattle were sprayed four times in a two-week period either with 2% geraniol (125ml/cow) or a 15% mixture of short chain fatty acids (C8-C9-C10)(250ml/cow), and there were untreated control cattle. Trials were conducted in California and North Carolina for 3 summers. Short-term fly counts (same day) on treated cattle were reduced by 61-99%, depending on material and trial, and the fatty acid mixture provided better control than geraniol. Horn fly counts were suppressed for 1-3 d and rebounded somewhat after both treatments. Consecutive treatments showed evidence of persistent impact in California where herds were more isolated. Rebounds to pre-treatment levels 3-4 d after treatment occurred more often in North Carolina, where other infested cattle were closer to treated herds. By 3-4 d post-treatment, horn flies were reduced by 29-61% in California and 0-83% in North Carolina, relative to pre-treatment. Background behavior frequencies were assessed from hundreds of counts on untreated, infested California cattle, where horn flies were the only abundant biting fly. Behavior averages were 16.5 tail flicks, 7.6 skin twitches, 1.2 head throws, or 0.2 leg stamps per 2min observation period. At horn fly densities from about 200 to more than 1000 flies per animal (moderate to high numbers), fly defensive behaviors on control cattle were poorly related (or unrelated) to fly numbers. Immediately after repellent application, however, flies were almost absent and behavior frequencies dropped distinctly. Cattle fly defensive behaviors therefore seem to be quite sensitive to low (less than 100 flies/animal) horn fly densities, and behaviors would be a poor quantitative tool to track fly stress at moderate densities and above. Both geraniol and the fatty acids show promise for horn fly control, especially in organic agriculture. Treatments at 1-2 d intervals probably would keep infestations below the economic threshold (200 flies/cow).

Seasonality and Diapause of Musca autumnalis (Diptera: Muscidae) at its Southern Limits in North America, With Observations on Haematobia irritans (Diptera: Muscidae).

The face fly (Musca autumnalis De Geer) and horn fly (Haematobia irritans ([L.])) were studied at the southern edge of the face fly's North American range, examining southern California geographic distribution, seasonal activity on cattle and in dung, and diapause. Face flies were common only at Pomona (34°03'N, 117°48'W). Other irrigated pastures, even those only slightly inland from Pomona, were probably too warm for face flies, due to a steep west (cooler) to east (warmer) temperature gradient. Horn flies were abundant at all sites. Adult densities on cattle, adults emerging from dung pats, and prevalence of fly-positive pats were assessed for both fly species throughout a year at Pomona. Summer adult horn fly densities of 500-2,000 flies per cow, or face fly densities of 3-10 flies per face, were common. Summer prevalence of face fly-positive pats and horn fly-positive pats was about 20-40% and 30-70%, respectively. Face fly adults diapaused from late October until late March and early April. Horn flies probably diapaused as pupae from late October or early November to early-mid March, although some emerged in winter. Experimental cohorts of October-emerging adult face flies were held in a representative overwintering site. They exhibited hypertrophied fat body and undeveloped oocytes, which are characteristics of diapause, and survived until the following spring. The dominant diapause cues in face and horn flies are probably photoperiod and temperature. Despite warm winter temperatures that would permit activity of both species, and despite relatively long winter day lengths, face flies and most horn flies still diapaused at this latitude.

Musca autumnalis (Diptera: Muscidae) and the host-specific nematode Paraiotonchium autumnale (Tylenchida: Iotonchiidae) in southern California.

Musca autumnalis DeGeer were collected in the summer and fall of 2011 and 2012 from a beef cattle herd in southern California Visual counts of Musca spp. on cattle faces were documented, and sweep net samples of face flies and other Diptera were also collected from cattle faces. Face flies dominated in the net collections, and 5-30 flies per face were common between early July and October 2011. Adult female M. autumnalis were dissected and examined for the presence of the host-specific nematode Paraiotonchium autumnale (Nickle). Overall, 67 of 887 (7.6%) adult face fly females were parasitized. M. autumnalis' ability to survive in such a southerly latitude (34 degree N) could reflect the rather temperate weather (coastal effects) and frequently irrigated pastures at the experimental site in southern California Preliminary observations suggest that face flies disappear from cattle during winter, despite generally favorable temperatures for fly activity. This is a possible indication of diapause and should be examined further.