Insecticidal, Repellent and Antifeedant Activity of Essential Oils from Blepharocalyx cruckshanksii (Hook. & Arn.) Nied. Leaves and Pilgerodendron uviferum (D. Don) Florin Heartwood against Horn Flies, Haematobia irritans (Diptera: Muscidae)

Haematobia irritans is a cosmopolitan obligate blood-feeding ectoparasite of cattle and is the major global pest of livestock production. Currently, H. irritans management is largely dependent on broad-spectrum pesticides, which has led to the development of insecticide resistance. Thus, alternative control methods are needed. Essential oils have been studied as an alternative due to their wide spectrum of biological activities against insects. Thus, the main aim of this study was to evaluate the insecticidal, repellent and antifeedant activity of the essential oils from Blepharocalyx cruckshanksii leaves and Pilgerodendron uviferum heartwood against horn flies in laboratory conditions. The composition of the essential oils was analyzed using gas chromatography coupled to mass spectrometry. Accordingly, α-pinene (36.50%) and limonene (20.50%) were the principal components of the B. cruckchanksii essential oil, and δ-cadinol (24.16%), cubenol (22.64%), 15-copaenol (15.46%) and δ-cadinene (10.81%) were the most abundant compounds in the P. uviferum essential oil. Mortality of flies and feeding behavior were evaluated by non-choice tests, and olfactory response was evaluated using a Y-tube olfactometer. Both essential oils were toxic to horn flies, with LC50 values for B. cruckchanksii essential oil of 3.58 µL L−1 air at 4 h, and for P. uviferum essential oil of 9.41 µL L−1 air and 1.02 µL L−1 air at 1 and 4 h, respectively. Moreover, the essential oils exhibited spatial repellency in the olfactometer using only 10 µg of each oil, and these significantly reduced the horn fly feeding at all doses evaluated. Although further laboratory and field studies related to the insectistatic and insecticide properties of these essential oils against H. irritans are necessary, B. cruckshanksii leaves and P. uviferum heartwood essential oils are promising candidates for horn fly management.

PSI-2 Spices in Free-choice Mineral Offer Gain Advantages to Cattle on Tallgrass Native Range and Promise as Fly Control

This study aims to evaluate effectiveness of two operational management systems for steer gains and fly control. The first strategy evaluated was pasture burn date of March (MAR) or April (APR). The second management strategy was fly control through feeding free-choice mineral with spices (SPICE) or without spices (CON). Eight pastures (n = 281 steers; initial weight 277.7 ± 25.2 kg) were used in a 2 x 2 factorial treatment structure. Steers were weighed individually, randomly assigned to treatment, and grazed for 85 days. Weekly 33% of steers per pasture were photographed and fly numbers counted. ADG was impacted by both burn date and mineral type (P = 0.01). Cattle on the APR-SPICE treatment had a greater ADG than MAR-SPICE and APR-CON with MAR-CON intermediate. Cattle on SPICE gained 4.5 kg (P = 0.12) more than cattle consuming CON mineral. Flies per steer were impacted by burn x mineral x week (P < 0.001). In general, APR-SPICE steers had a greater number of flies weeks 8, 10, and 11 (P < 0.05), corresponding to a time when mineral intake averaged 72% of the formulated intake. The MAR-SPICE steers consumed on average the formulated amount of mineral and through the entire grazing period had lower number of flies than APR-SPICE steers (P < 0.05). The second largest ADG observed with the MAR-CON treatment may be attributed to lower fly numbers as this treatment had one extra week below economic threshold for horn flies. These results are somewhat inconclusive on pasture burn date, but show that the addition of spices to a free-choice complete mineral shows promise as a cost-effective method to increase gains in stocker steers on tallgrass native range. As a fly control method, the spices utilized in this study may be effective if intake is at formulated level.

Antifeedant Effects and Repellent Activity of Loline Alkaloids from Endophyte-Infected Tall Fescue against Horn Flies, Haematobia irritans (Diptera: Muscidae)

Haematobia irritans is an obligate bloodsucking ectoparasite of cattle and is the global major pest of livestock production. Currently, H. irritans management is largely dependent upon broad-spectrum pesticides, which lately has led to the development of insecticide resistance. Thus, alternative control methods are necessary. Endophyte-infected grasses have been studied as an alternative due to their capability to biosynthesize alkaloids associated with anti-insect activities. Thus, the main aim of this study was to evaluate the antifeedant and repellent activity of lolines obtained from endophyte-infected tall fescue against H. irritans adults in laboratory conditions. The alkaloid extract (ALKE) was obtained by acid–base extraction. N-formyl loline (NFL) and N-acetyl loline (NAL) were isolated by preparative thin layer chromatography (pTLC) and column chromatography (CC), and the loline was prepared by acid hydrolysis of a NFL/NAL mixture. Loline identification was performed by gas chromatography coupled to mass spectrometry (GC/MS). Feeding behavior was evaluated by a non-choice test, and olfactory response was evaluated using a Y-tube olfactometer. Accordingly, all samples showed antifeedant activities. NFL was the most antifeedant compound at 0.5 µg/µL and 1.0 µg/µL, and it was statistically equal to NAL but different to loline; however, NAL was not statistically different to loline. NFL and NAL at 0.25 µg/µL were more active than loline. All samples except loline exhibited spatial repellency in the olfactometer. Thus, the little or non-adverse effects for cattle and beneficial activities of those lolines make them suitable candidates for horn fly management.

Susceptibility of field populations of Haematobia irritans to fipronil in Uruguay

ABSTRACT: Fipronil was registered in Uruguay in 1997, and, since then, it has been used for the control of Haematobia irritans irritans and Rhipicephalus microplus. The susceptibility of H. irritants to this drug has not been evaluated. Therefore, the goal of the present study was to evaluate the resistance of H. irritans to fipronil. Additionally, a survey was carried out with the farmers to evaluate the use of fipronil for H. irritans control in the ranches where the flies came from. For the bioassays, 31 field populations of H. irritans were exposed to 10 concentrations of fipronil (3.2-16.0μg.cm2), and their LC50 values were calculated using probit analysis. A bioassay was performed with horn flies from the susceptible colony maintained at the USDA-ARS Knipling-Bushland U.S. Livestock Insects Research Laboratory for comparison and calculation of resistance ratios (RRs). All 31 field populations surveyed in the study were susceptible to fipronil, with resistance ratios ranging from <0.5 to 2.2. Four populations with RRs >1 did not differ significantly from the susceptible strain. A single population showed an RR >2.2. Overall, the survey shows that fipronil was mostly used for R. microplus control, and in only three ranches, which were free of R. microplus, was fipronil used for horn fly control. Seventeen farmers did not use fipronil at all in the last three years. It is concluded that, in Uruguay, field populations of horn flies remain susceptible to fipronil.

Chemosensory-Related Gene Family Members of the Horn Fly, Haematobia irritans irritans (Diptera: Muscidae), Identified by Transcriptome Analysis

Horn flies are one of the most significant economic pests of cattle in the United States and worldwide. Chemical control methods have been routinely utilized to reduce populations of this pest, but the steady development of insecticide resistance has prompted evaluation of alternative control strategies. Behavior modifying compounds from natural products have shown some success in impacting horn fly populations, and a more thorough understanding of the horn fly chemosensory system would enable improvements in the development of species-specific compounds. Using an RNA-seq approach, we assembled a transcriptome representing genes expressed in adult female and male horn fly head appendages (antennae, maxillary palps, and proboscides) and adult fly bodies from which heads were removed. Differential gene expression analysis identified chemosensory gene family members that were enriched in head appendage tissues compared with headless bodies. Candidate members included 43 odorant binding proteins (OBP) and 5 chemosensory binding proteins (CSP), as well as 44 odorant receptors (OR), 27 gustatory receptors (GR), and 34 ionotropic receptors (IR). Sex-biased expression of these genes was not observed. These findings provide a resource to enable future studies targeting horn fly chemosensation as part of an integrated strategy to control this blood-feeding pest.

48 Genetic study of horn fly abundance in beef cattle

Disturbing the non-symbiotic relationship between horn flies and cattle is of economic, health, and animal welfare importance. Reliance on management and insecticides has proven inadequate. In the United States, horn flies are estimated to cause more than $1 billion in economic losses on pastured cattle annually. Although insecticides provide temporary control, their efficacy is hampered by several factors. Intensive insecticide use has led to horn fly resistance and decreased predation on horn flies by other insects. Due to the cost and logistic complexity of measuring fly resistance traits under commercial conditions, the genetic basis of these traits remains largely unknown. Only a few heritability estimates are available based on small-scale studies. Currently, the economic injury threshold (EIT) due to horn fly abundance (onset of production decay) is set at around 200 flies for beef cattle. This threshold is largely heuristically set. Additionally, the rate of decay in performance as a function of fly abundance after injury onset is unknown. It is also likely that EIT is breed and animal specific. Data used in this study was collected during the summer of 2019. Animals were not treated or managed in any way to control horn flies prior to data collection. Animals were assessed subjectively and based on image counts for horn fly abundance. Estimates of heritability of horn fly abundance ranged between 0.14 and 0.22 for subjective and image-based phenotypes. The lowest heritability was for the subjective assessment, likely due to the excessive variation between evaluators. Changepoint model-based analysis showed that EIT is variable between sire families, ranging from 265 to 413 flies. Furthermore, there was significant difference in the decay of performance after the onset of injury. The rate of decay ranged between -0.0003 and -0.00018. Collectively, these results indicate the potential to improve horn fly resistance/tolerance using genetic tools.

Laboratory Methods for Rearing Horn Flies (Diptera: Muscidae)

The horn fly, Haematobia irritans (L.), is an obligate hematophagous ectoparasite of cattle, and one of the most important pests of cattle causing unrealized gains or losses in meat and milk production. The present study describes the difficulties that arise when research programs have attempted to maintain this pest, both on-host and off-host, in a laboratory environment. Suggestions aimed at assisting future researchers in successfully colonizing horn flies in the laboratory are provided.

Establishing a Method to Evaluate the Efficacy of Compounds Aimed at Repelling Horn Fly (Diptera: Muscidae) Infestations on Cattle in a Laboratory Setting

Use of nonpesticidal chemicals to minimize or eliminate horn fly (Haematobia irritans) populations on cattle could be helpful in combating insecticide resistance. One recent approach is the use of natural products with repellent properties against the target pest. A rapid on-animal evaluation system that accounts for both host and pest interactions and bypasses the need for costly multiyear field assessments is needed. The objective of this study was to develop a system to quantify product repellency of horn flies on cattle in a laboratory setting. Animal pair treatment groups were utilized to assess product efficacy and carrier effects across three experimental trials. A treatment solution consisting of 3% geraniol in mineral oil was the natural product repellent. Horn fly populations on animal pairs receiving the geraniol treatment were significantly reduced when compared with untreated animal pairs. However, animal pairs receiving a mineral oil-only treatment showed reduced horn fly populations similar to animals treated with mineral oil plus geraniol. Thus, there was a strong carrier effect that could be difficult to distinguish in the field but was easily observed using laboratory methods.

Haematobium irritans and Haematobium titillans as potential vectors of Parabronema skrjabini in camels (Camelus bactrianus) in Inner Mongolia, China

Parabronema skrjabini is one of the most harmful nematodes to camels and is responsible for economic losses in animal husbandry industry. There is an urgent need for in-depth studies of potential vectors of the nematode due to its scant regarding information. As previous studies indicated that flies may be the vectors of P. skrjabini, we captured flies in the main camel-producing areas of Inner Mongolia. After autopsy of the specimens of two species of horn flies, we observed the morphology of the suspected nematode larvae found in them. Internal transcribed spacer ribosomal-DNA gene sequences were considered the best candidate to confirm the species of the larvae found. Our results showed that the homology compared with P. skrjabini was 99.5% in GenBank. Subsequently, we preliminarily identified two species of horn flies through morphological observation and then sequenced the mitochondrial-DNA-gene cytochrome oxidase subunit I obtained from two species of horn flies, with 100 and 99.2% similarity to sequences deposited in GenBank, respectively. Thus, we identified Haematobia titillans and Haematobia irritans and provided evidence for their potential role as vectors of parabronemosis. Our study provides reference for future research on the life history of the nematode and the vectors of parabronemosis.