Limits to ambulatory displacement of coconut mites in absence and presence of food-related cues

First trials exploring the potential of phytoseiid mites in managing lychee erinose mite, Aceria litchii (Keifer) (Acari: Eriophyidae), infestations on lychee plants

Phytoseiid mites have been frequently found in association with the lychee erinose mite, Aceria litchii, on lychee plants in Brazil, suggesting that they are promising candidates as biological control agents against this pest. Here, we investigated whether phytoseiids would suppress A. litchii infestation, i.e. formation of erinea, on lychee plants under field conditions. Four groups of A. litchii-infested plants were randomly distributed in the field, with each group receiving either Phytoseius intermedius, Amblyseius herbicolus, A. herbicolus supplemented with cattail pollen or no predator. During a three-month period, the released predators, along with others present in the surrounding environment, were allowed to freely walk among all plants. In each plant, we evaluated the occurrence of phytoseiid species, their abundance, and the dynamics of erinea formation. A total of 2,097 mites, including 13 other phytoseiid species were identified. The most abundant species were Iphiseiodes zuluagai and Euseius ho, rather than the two predator species that were released. A. herbicolus and P. intermedius failed to establish populations in the majority of the plants, regardless of the presence of pollen, suggesting their ineffectiveness in controlling A. litchii infestations. While there was a significant difference in the proportion of erinea among the four treatments, this contrast was not associated with the presence of phytoseiids, suggesting that other factors might have hindered erinea formation on lychee plants. The reasons behind this outcome are further explored and discussed.

Removing grass clippings reduces bermudagrass mite (Acari: Eriophyidae) infestation during turfgrass regrowth

Bermudagrass mite (Aceria cynodoniensis Sayed) infestation stunts bermudagrass (Cynodon spp. [Poales: Poaceae]) growth, leading to thinned turf and lower aesthetic and recreational value. Bermudagrass mites cause characteristic symptoms called witch's brooms, including shortened internodes and leaves and the proliferation of tillers. Grass clippings produced by mowing or scalping bermudagrass harbor mites, which abandon the desiccating grass clippings and spread to surrounding turfgrass. Dropped grass clippings can lead to infestation of new turfgrass. Nursery experiments were conducted with potted bermudagrass to determine the effect of removing witch's brooms or grass clippings after scalping on witch's broom densities on the recovering bermudagrass. Additionally, laboratory experiments were conducted to assess the potential for mites to abandon detached witch's brooms and to evaluate mite survival after leaving their hosts. The number of initial witch's brooms and individually removing witch's brooms did not affect subsequent witch's broom densities, suggesting that infested but asymptomatic terminals later developed into witch's brooms. Removing grass clippings after scalping reduced witch's broom densities by over 65% in two trials. Most mites (96%) abandoned witch's brooms within 48 h after detaching witch's brooms, and adult mites survived an average of 5.6 h after removal from the host plant. Removing clippings after scalping may improve bermudagrass mite management and limit damage on the recovering turfgrass. Additionally, clippings resulting from regular mowing or scalping should be disposed of properly because this study demonstrates that mites abandon desiccating host plants and survive sufficiently long to infest surrounding turfgrass.

Population dynamics of Steneotarsonemus concavuscutum, a neglected mite pest in coconut fruits (Cocos nucifera)

The meristematic region of Cocos nucifera fruits can be colonized by various species of mites, including Steneotarsonemus concavuscutum, Steneotarsonemus furcatus, and Aceria guerreronis. The consequence of this colonization is the development of necrotic lesions on the fruit, and sometimes its abortion. Losses are commonly attributed to A. guerreronis alone, owing to the similarities in the injuries caused and its predominance in coconut plantations. However, S. concavuscutum may be the predominant pest species in some crops. Despite the possible impact of S. concavuscutum, little is known about its bioecological aspects, such as the influence of biotic and abiotic factors on its population dynamics. Our objective was to document macroclimatic abiotic factors (temperature, relative humidity, and precipitation) and biotic factors (interspecific competition and predation) interfere in the population dynamics of S. concavuscutum. We evaluated the diversity and abundance of mites in the perianth of coconut fruit naturally infested by S. concavuscutum for 1 year. The species found in the fruits of bunch 6 of the plant, which is the fruit age at which the mites commonly reach the highest abundance, were counted every 2 weeks. We found mites from nine families and S. concavuscutum was the predominant species, representing about 92% of the individuals collected. Predators represented approximately 2% of the total collection, with Neoseiulus baraki as the predominant species. Steneotarsonemus concavuscutum population density ranged from 60 to 397 mites/fruit. The highest population densities of S. concavuscutum were observed in the hottest and driest periods of the year. The population densities of S. concavuscutum were negatively associated with the presence of N. baraki, suggesting that this predator may have a role in the biological control of this pest.

Hitchhiking or hang gliding? Dispersal strategies of two cereal-feeding eriophyoid mite species

Dispersal shapes the dynamics of populations, their genetic structure and species distribution; therefore, knowledge of an organisms' dispersal abilities is crucial, especially in economically important and invasive species. In this study, we investigated dispersal strategies of two phytophagous eriophyoid mite species: Aceria tosichella (wheat curl mite, WCM) and Abacarus hystrix (cereal rust mite, CRM). Both species are obligatory plant parasites that infest cereals and are of economic significance. We investigated their dispersal success using different dispersal agents: wind and vectors. We hypothesised that in both mite species the main mode of dispersal is moving via wind, whereas phoretic dispersal is rather accidental, as the majority of eriophyoid mite species do not possess clear morphological or behavioural adaptations for phoresy. Results confirmed our predictions that both species dispersed mainly with wind currents. Additionally, WCM was found to have a higher dispersal success than CRM. Thus, this study contributes to our understanding of the high invasive potential of WCM.

What Could Arrest an Eriophyoid Mite on a Plant? The Case of Aculops allotrichus from the Black Locust Tree

Simple Summary

For a phytophagous arthropod, plant cues and the presence of conspecifics or heterospecifics on a plant are important sources of information about food availability and predation risk. In eriophyoid mites, which are a group of economically important plant parasites, this issue is still poorly understood. In the previous study, females of the eriophyoid Aculops allotrichus prolonged their stay on unprofitable, old black locust leaves with injured conspecifics, suggesting their specific attraction to pierced individuals. The aim of this study was to shed light on this phenomenon. The series of tests using intact and artificially injured conspecifics, heterospecifics, pollen and sand grains revealed the high specificity of cues associated with mite injury. Only the presence of conspecifics triggered female arrestment on unprofitable old leaves, and this effect was more pronounced on leaf patches with injured than with intact eriophyoids. To our best knowledge, A. allotrichus is the first described herbivore in which injured conspecifics, instead of causing an alarm to be raised, keep the foraging individuals within a risky patch. Our tests using three non-host plants also suggest that A. allotrichus presumably needs more time to identify and evaluate non-host plants than host plants.

Abstract

Aculops allotrichus is a vagrant eriophyoid that lives gregariously on the leaves of the black locust tree. This study demonstrated that conspecifics can have a significant impact on A. allotrichus females on unprofitable, old black locust leaves and can arrest them on those leaves. The effect was more pronounced in females that were exposed to artificially injured individuals than to intact ones. They not only prolonged their sojourn on leaf discs with pierced conspecifics, but also preferred the leaf disc halves with damaged individuals to clean ones. Aculops allotrichus is the first described herbivore in which artificially injured conspecifics, instead of causing alarm, keep the foraging individuals within a risky patch. Other objects, such as artificially injured or intact heterospecifics, pollen or sand, were irrelevant to the eriophyoid females on old leaf patches. In tests with old leaves of maple, magnolia and hard kiwi vine, the females postponed their movement from non-host leaf discs, which suggests that they may need more time to recognise and evaluate unfamiliar plants than familiar ones.

Wind speed predicts population dynamics of the eriophyid mite Floracarus perrepae on invasive Old World climbing fern (Lygodium microphyllum) in a shade house colony

Lygodium microphyllum is one of the most noxious invasive plants in Florida, USA, smothering native vegetation in cypress swamps, pine flatwoods, and Everglades tree islands and altering fire regimes. The eriophyid mite Floracarus perrepae was introduced from Australia to help control L. microphyllum infestations. While F. perrepae exhibits high population growth rates in its native range, its population dynamics in Florida are unknown, particularly the dynamics that occur within the leaf roll galls the mite induces on the margins of leaves. Here, we monitored a shade house colony of F. perrepae in south Florida for 2 years to identify seasonal patterns and potential climate drivers of within-gall mite density. Gall dissections of mite-infested colony plants were performed monthly. Mite density within galls exhibited two cycles per year: a strong cycle that boomed in spring and busted in summer, and a weak cycle that moderately increased mite density in fall and declined in winter. Climate variables, particularly those related to wind speed, were positively associated with higher mite density. Our study sheds light on the within-gall dynamics of F. perrepae and suggests that the highest within-gall mite densities occur in the spring and fall.

Predator performance is impaired by the presence of a second prey species

The simultaneous infestation of a plant by several species of herbivores may affect the attractiveness of plants to the natural enemies of one of the herbivores. We studied the effect of coconut fruits infested by the pests Aceria guerreronis and Steneotarsonemus concavuscutum, which are generally found together under the coconut perianth. The predatory mite Neoseiulus baraki produced lower numbers of offspring on fruits infested with S. concavuscutum and on fruits infested with both prey than on fruits with A. guerreronis only. The predators were attracted by odours emanating from coconuts with A. guerreronis, but not by odours from coconuts with S. concavuscutum, even when A. guerreronis were present on the same fruit. Fewer N. baraki were recaptured on fruits with both prey or with S. concavuscutum than on fruits with only A. guerreronis. Furthermore, the quality of A. guerreronis from singly and multiply infested coconuts as food for N. baraki did not differ. Concluding, our results suggest that N. baraki does not perform well when S. concavuscutum is present on the coconuts, and the control of A. guerreronis by N. baraki may be negatively affected by the presence of S. concavuscutum.

Evidence of Amblyseius largoensis and Euseius alatus as biological control agent of Aceria guerreronis

Amblyseius largoensis (Muma) (Acari: Phytoseiidae) and Euseius alatus De Leon (Acari: Phytoseiidae) are predatory mites that are mostly found on leaves and on the exposed fruit surface of coconut plants. Their morphology hampers the access to the microhabitat occupied by Aceria guerreronis Keifer (Acari: Eriophyidae), the most important pest of coconut fruits throughout the world. However, it was suggested that they can prey on A. guerreronis under natural conditions when this pest leaves its refuge to disperse. Since the trophic interactions between A. largoensis or E. alatus and A. guerreronis are unknown, we compare the frequencies of occurrence of A. largoensis and E. alatus under the bracts of coconut fruits and on coconut leaflets. In addition, because phytoseiids feed by liquid ingestion, we used molecular analysis to confirm the potential role of A. largoensis or E. alatus as predators of A. guerreronis and to assess how fast the A. guerreronis DNA fragment is degradated in the A. largoensis digestive tract. Our study demonstrated that E. alatus was only present on coconut leaflets whereas A. largoensis was found mostly on leaflets and, to a much lesser extent, under the bracts of coconuts. Species-specific ITS primers designed for A. guerreronis were shown to have a high degree of specificity for A. guerreronis DNA and did not produce any PCR product from DNA templates of the other insects and mites associated with the coconut agroecosystem. Based on molecular analysis, we confirmed that the predatory mites, A. largoensis and E. alatus, had preyed on the coconut mite in the field. Overall the predatory mites collected in the field exhibited low levels of predation (26.7% of A. largoensis and 8.9% of E. alatus tested positive for A. guerreronis DNA). The fragment of A. guerreronis DNA remained intact for a very short time (no more than 6 h after feeding) in the digestive tract of A. largoensis.

The Effect of Temperature, Relative Humidity, and Virus Infection Status on off-host Survival of the Wheat Curl Mite (Acari: Eriophyidae)

The wheat curl mite, Aceria tosichella Keifer, is an eriophyid pest of wheat, although its primary economic impact on wheat is due to the transmission of Wheat streak mosaic (WSMV), Wheat mosaic (also known as High Plains virus), and Triticum mosaic (TriMV) viruses. These viruses cause significant annual losses in winter wheat production throughout the western Great Plains. Temperature and humidity are factors that often influence arthropod survival, especially during dispersal from their hosts, yet the impact of these two factors on off-host survival has not been documented for wheat curl mite. Pathogen-infected host plants often influence the biology and behavior of vectors, yet it is not known if virus-infected wheat affects off-host survival of wheat curl mite. The objectives of this study were to 1) determine if temperature, relative humidity, and mite genotype impact off-host survival of wheat curl mite and 2) determine the effect of WSMV- and TriMV-infected host plants on off-host survival of wheat curl mite. Temperature and relative humidity significantly affected off-host survival of wheat curl mite. Length of survival decreased with increasing temperature (106.2 h at 10°C and 17.0 h at 30°C) and decreasing relative humidity (78.1 h at 95 and 21.3 h at 2%). Mites from TriMV-infected host plants had ∼20% reduction in survival at 20°C compared with those from WSMV-infected plants. The duration of off-host survival of wheat curl mite is influenced by environmental conditions. Management strategies that target a break in host presence will greatly reduce mite densities and virus spread and need to account for these limits.

Host finding behaviour of the coconut mite Aceria guerreronis

For the coconut mite, Aceria guerreronis Keifer, its host plant, the coconut palm, is not merely a source of food, but more generally a habitat to live in for several generations. For these minute organisms, finding a new plant is difficult and risky, especially because their main mode of dispersal is passive drifting with the wind and because they are highly specialized on their host plant. Consequently, the probability of landing on a suitable host is very low, let alone to land in their specific microhabitat within the host. How coconut mites manage to find their microhabitat within a host plant is still underexplored. We tested the hypothesis that they use volatile chemical information emanating from the plant to find a specific site within their host plants and/or use non-volatile plant chemicals to stay at a profitable site on the plant. This was investigated in a Y-tube olfactometer (i.e. under conditions of a directed wind flow) and on cross-shaped arenas (i.e. under conditions of turbulent air) that either allowed contact with odour sources or not. The mites had to choose between odours from specific parts (leaflet, spikelet or fruit) of a non-infested coconut plant and clean air as the alternative. In the olfactometer experiments, no mites were found to reach the upwind end of the Y-tube: <5 % of the mites were able to pass the bifurcation of the "Y". On the cross-shaped arenas, however, a large number of coconut mites was found only when the arm of the arena contained discs of fruit epidermis and contact with these discs was allowed. The results suggest that coconut mites on palm trees are not attracted to specific sites on the plant by volatile plant chemicals, but that they arrested once they contact the substrate of specific sites. Possibly, they perceive non-volatile chemicals, but these remain to be identified.

Behaviour of coconut mites preceding take-off to passive aerial dispersal

For more than three decades the coconut mite Aceria guerreronis Keifer is one of the most important pests of coconut palms and has recently spread to many coconut production areas worldwide. Colonization of coconut palms is thought to arise from mites dispersing aerially after take-off from other plants within the same plantation or other plantations. The underlying dispersal behaviour of the mite at take-off, in the airborne state and after landing is largely unknown and this is essential to understand how they spread from tree to tree. In this article we studied whether take-off to aerial dispersal of coconut mites is preceded by characteristic behaviour, whether there is a correlation between the body position preceding aerial dispersal and the direction of the wind, and whether the substrate (outer surface of coconut bracts or epidermis) and the wind speed matter to the decision to take-off. We found that take-off can sometimes be preceded by a raised body stance, but more frequently take-off occurs while the mite is walking or resting on its substrate. Coconut mites that become airborne assumed a body stance that had no relation to the wind direction. Take-off was suppressed on a substrate providing food to coconut mites, but occurred significantly more frequently on the outer surface of coconut bracts than on the surface of the fruit. For both substrates, take-off frequency increased with wind speed. We conclude that coconut mites have at least some degree of control over take-off for aerial dispersal and that there is as yet no reason to infer that a raised body stance is necessary to become airborne.