Experimental and Applied Acarology

Overwintering and diapause are variable among mite species and strains. The aims of this study were to determine whether certain crops constitute overwintering sites for the Argentine strain of the predator Neoseiulus californicus and whether females underwent reproductive diapause in winter. Neoseiulus californicus was recorded monthly on the vegetables tomato, sweet pepper, eggplant, and artichoke, and on strawberry, among other crops in Buenos Aires province, Argentina. This mite was found at a lower percentage of crops in the winter than in the other seasons. Since the predator was quite frequent on artichoke, this crop could constitute a refuge during adverse environmental conditions. The mite’s frequency on several crops in other seasons and potential association with a strawberry pest is discussed. In the laboratory, individuals exposed to winter conditions throughout the life cycle exhibited a long pre-oviposition period and low oviposition rate, but did not diapause. After being kept under winter conditions from larva to adult, when individuals were transferred to the optimal spring temperatures and lighting, the pre-oviposition period was shorter and the fecundity higher than under winter conditions. When individuals remained under spring conditions from larva to adult and were then transferred to the winter parameters during the first 15 days of adulthood, the pre-oviposition period was long and the oviposition rate low. Once the optimal conditions were restored, the daily fecundity became similar to that of the individuals remaining under optimal conditions throughout the life cycle. Fecundity of N. californicus decreased significantly under winter conditions but reproductive diapause was not observed.

The cattle tick Rhipicephalus microplus is currently invading the West African region, and little information is available on the spread of this exotic tick in this region. We set out a country-wide field survey to determine its current distribution in Benin. Ticks were collected on cattle from 106 farms selected by random sampling covering all regions of the country. Rhipicephalus annulatus was found on 70 % of all farms, R. decoloratus on 42 %, R. geigyi on 58 %, and R. microplus on 49 %. There is a clear geographic separation between the indigenous Rhipicephalus species and R. microplus. Rhipicephalus annulatus occurs mainly in the northern departments, but it was also observed in lower numbers in locations in the south. The presence of R. decoloratus is limited to the northern region, and in most locations, this tick makes up a small proportion of the collected ticks. The tick R. geigyi tends to be dominant, but occurs only in the four northern departments. The observations concerning R. microplus are entirely different, this species occurs in the southern and central region. The results of this survey confirm the invasive character and displacement properties of R. microplus, since in less than a decade it has colonized more than half of the country and has displaced indigenous ticks of the same genus in many of the sampled locations.

Drag sampling and flagging are two of the most effective and widely applied techniques to monitor tick populations. Despite the importance of this sampling strategy, there is a lack of standardized protocols for the construction of an inexpensive tick drag/flag. To this end, we provide a step-by-step protocol that details the construction of a tick drag/flag. We provide evidence of efficacy by comparing results obtained over 3-months at 108 locations within the William B. Bankhead National Forest, Alabama, USA. Overall, our drag/flag sampling approach yielded 1127 larvae, 460 nymphs, and 53 adults for a total of 1640 ticks representing three species. We detected significant patterns in Amblyomma americanum abundance for nymphs and adults with greater counts in June (β = 0.91 ± 0.36, 95% CI 0.55–1.27; β = 2.44 ± 0.63, 95% CI 1.81–3.07, respectively) and July (β = 0.73 ± 0.36, 95% CI 0.37–1.09; β = 1.65 ± 0.66, 95% CI 0.99–2.31, respectively) as compared to August. We also detected a significant difference in tick captures by tick drag/flag fabric type with greater captures when muslin was used as compared to flannel (β = 1.07 ± 0.06, 95% CI 1.01–1.13). Our goal is to provide instructions to assemble a highly effective tick drag/flag using minimal supplies. Evaluation and improvements of sampling techniques is essential to understand impacts of landscape management and larger stressors, such as climate change on tick populations but also for enhancing detection of invasive non-native species.

Reproductive success and population growth of an herbivorous mite are limited by activities of phytoseiid predators. However, occurrences on upper versus lower leaf surfaces are sometimes mismatched between these prey and predators. The mismatch potentially mitigates predation risk for the prey species. We assessed factors that affect mite distributions on leaf surfaces, testing whether the presence of the phytoseiid mite Phytoseius nipponicus alters the leaf-surface distribution and reproductive success of the herbivorous false spider mite Brevipalpus obovatus. The host plant was Viburnum erosum var. punctatum (Adoxaceae). Leaves were set in natural (TRUE) and reversed (upside down; INVERTED) orientations using experimental devices. Both surfaces were accessible to mites. We detected lower and abaxial leaf-surface preferences in P. nipponicus. In contrast, upper and adaxial surfaces were preferred by B. obovatus. Thus, prey and predatory mites accumulated on different sides of leaves. Presence of the predator also indirectly decreased egg production in B. obovatus. Brevipalpus obovatus females actively avoided leaf surfaces with elevated predator numbers; these females shifted their distributions and changed oviposition sites to leaf surfaces with fewer predators. In consequence, B. obovatus eggs on the upper sides of leaves were less frequently preyed upon than were those on lower sides. We suggest that upper leaf-surface exploitation in this particular herbivorous mite species mitigates predation risk from phytoseiid mites, which prefer lower leaf surfaces.

Rabbits developed resistance toRhipicephalus appendiculatus instars following repetitive infestations. Rejection was accompanied by elevated IgM and IgG titres. Extracts of salivary gland, mouthpart cement and whole ticks induced a dose-related lymphocyte transformation. Skin-provocation tests with tick extracts elicited an immediate type-I hypersensitivity reaction with a delayed time-course which was influenced by antihistamines. Passive-transfer studies indicated that resistance was partially transferred with serum. A comparative histological study of the attachment sites of larvae on resistant and naive hosts demonstrated the role of eosinophils and macrophages during the initial phase of infestation. Possible rejection mechanisms are discussed in the light of these and other findings.

Balaustium medicagoense and Bryobia spp. have recently been identified as emerging pests of winter crops and pastures in Australia. These mites have a high natural tolerance to currently registered pesticides, highlighting the need to develop alternative control strategies such as cultural controls which require an understanding of plant associations. In shade-house experiments, Bryobia spp. survived and reproduced successfully on pasture, lupins and oats, but progeny failed to reach the adult stage on canola and wheat. Balaustium medicagoense progeny failed to produce a generation on any crop but parental adults survived a few months on all crops, particularly wheat. Bryobia spp. damaged canola, pasture and lupins, but caused minimal damage to oats and wheat, whereas Ba. medicagoense caused considerable damage to wheat and lupins, but only moderate damage to canola, oats and pasture. Field survey data, taken from approximately 450 sites across southern Australia, combined with analysis of historical pest reports, suggest broadleaf crops such as canola, lucerne, lupins and weeds appear particularly susceptible to attack by Bryobia species. Balaustium medicagoense was more commonly found on cereals and grasses, although they also attacked broadleaf crops, particularly canola, lucerne and lupins. These findings show that the mites have the potential to be an important pest on several winter grain crops and pasture, but there are important differences that can assist in management strategies such as targeted crop rotations.