Mite Mononychellus Tanajoa Research Articles

Inheritance of resistance to cassava green mite and other useful agronomic traits in cassava grown in Zambia

Cassava green mite (CGM) Mononychellus tanajoa (Bondar) (Acari: Tetranychidae) is a major arthropod pest causing significant loss in the yields of storage roots and planting materials of cassava in Zambia. Its control has been mainly based on the use of exotic predatory mites as biological control agents, which unfortunately, have not established well in Zambia due to the lack of suitable host genotypes and harsh weather conditions. The current study was aimed at breeding cassava for improvement of morphological traits that are associated with resistance to CGM, which can also enable cassava genotypes to provide shelter and ensure continuous survival of natural enemies of CGM, and to determine the inheritance of these traits by assessing combining ability and therefore the type of gene action involved in their expression. Using a 5 × 5 half diallel mating design, full-sib cassava genotypes were generated out of which 300 were selected and evaluated in the field. Data were collected for CGM density, CGM leaf damage and cassava mosaic disease severity, plant growth habit, leaf morphological traits, storage root yield and root dry mass. Both general and specific combining ability effects were significant (P < 0.01) for the reaction of the F1 progeny to CGM, and for the various plant morphological traits that were measured, suggesting that both additive and non-additive gene effects play a role in the expression of the traits.

Potential geographic distribution of two invasive cassava green mites.

The cassava green mites Mononychellus tanajoa and M. mcgregori are highly invasive species that rank among the most serious pests of cassava globally. To guide the development of appropriate risk mitigation measures preventing their introduction and spread, this article estimates their potential geographic distribution using the maximum entropy approach to distribution modeling. We compiled 1,232 occurrence records for M. tanajoa and 99 for M. mcgregori, and relied on the WorldClim climate database as a source of environmental predictors. To mitigate the potential impact of uneven sampling efforts, we applied a distance correction filter resulting in 429 occurrence records for M. tanajoa and 55 for M. mcgregori. To test for environmental biases in our occurrence data, we developed models trained and tested with records from different continents, before developing the definitive models using the full record sets. The geographically-structured models revealed good cross-validation for M. tanajoa but not for M. mcgregori, likely reflecting a subtropical bias in M. mcgregori's invasive range in Asia. The definitive models exhibited very good performance and predicted different potential distribution patterns for the two species. Relative to M. tanajoa, M. mcgregori seems better adapted to survive in locations lacking a pronounced dry season, for example across equatorial climates. Our results should help decision-makers assess the site-specific risk of cassava green mite establishment, and develop proportional risk mitigation measures to prevent their introduction and spread. These results should be particularly timely to help address the recent detection of M. mcgregori in Southeast Asia.

Functional response of Euseius concordis to densities of different developmental stages of the cassava green mite

Both prey density and developmental stage of pests and natural enemies are known to influence the effectiveness of biological control. However, little is known about the interaction between prey density and population structure on predation and fecundity of generalist predatory mites. Here, we evaluated the functional response (number of prey eaten by predator in relation to prey density) of adult females and nymphs of the generalist predatory mite Euseius concordis to densities of different developmental stages of the cassava green mite Mononychellus tanajoa, as well as the fecundity of adult females of the predator. We further assessed the instantaneous rate of increase, based on fecundity and mortality, of E. concordis fed on eggs, immatures and adults of M. tanajoa. Overall, nymphs and adults of E. concordis feeding on eggs, immatures and females of M. tanajoa had a type III functional response curve suggesting that the predator increased prey consumption rate as prey density increased. Both nymphs and adult females of the predator consumed more eggs than immatures of M. tanajoa from the density of 20 items per leaf disc onwards, revealing an interaction between prey density and developmental stage in the predatory activity of E. concordis. In addition, population growth rate was higher when the predator fed on eggs and immatures in comparison with females. Altogether our results suggest that E. concordis may be a good candidate for the biological control of M. tanajoa populations. However, the efficiency of E. concordis as a biological control agent of M. tanajoa is contingent on prey density and population structure.

Single versus multiple enemies and the impact on biological control of spider mites in cassava fields in West-Africa

To determine whether to use single or multiple predator species for biological pest control requires manipulative field experiments. We performed such tests in Benin (West Africa) in cassava fields infested by the cassava green mite Mononychellus tanajoa, and the cotton red mite Oligonychus gossypii. These fields also harboured the cassava apex-inhabiting predator Typhlodromalus aripo and either the leaf-inhabiting predator Amblydromalus manihoti or Euseius fustis. We manipulated predator species composition on individual plants to determine their effect on prey and predator densities. In fields with T. aripo plus A. manihoti, M. tanajoa densities were reduced by T. aripo alone or together with A. manihoti, but neither of these predators, alone or together, reduced O. gossypii densities. In fields with T. aripo plus E. fustis, T. aripo alone or together with E. fustis exerted significant control over O. gossypii, but weak control over M. tanajoa. Densities of any of the predator species were not affected by co-occurring predator species, suggesting a minor role for intraguild predation in the field, contrary to earlier experiments on small plants in the laboratory. We conclude that (1) T. aripo is the most effective predator species in suppressing M. tanajoa, (2) two predator species, T. aripo and E. fustis, are needed to suppress O. gossypii, and (3) predator species together on the same plant do not negatively affect each other nor the extent to which they control their prey. We argue that intraguild predation is reduced due to partial niche separation among predator species.

Mix-planting pubescent and glabrous cassava affects abundance ofTyphlodromalus aripoand its prey miteMononychellus tanajoa

There is an increasing awareness that vegetation diversity can affect herbivore and natural enemy abundance and that plants can play a major role in directly manipulating natural enemy abundance for protection against herbivore attacks. Using data from cassava fields, we aimed at (i) testing the capacity of the predatory mite Typhlodromalus aripo to control the herbivorous mite Mononychellus tanajoa in a chemical exclusion trial; and (ii) testing, based on the differential preference by T. aripo for cassava cultivars, how combinations of two morphologically different cassava cultivars with differential suitability to the predator can improve its population densities on the non-favourable cultivar, thereby reducing M. tanajoa densities with subsequent increases in cassava yield. The study was conducted in a cassava field in Benin, West Africa. The experiments confirmed that T. aripo effectively suppresses M. tanajoa populations on both cultivars and showed, in the no-predator-exclusion experiments, that cultivar combinations have significant effects on M. tanajoa and T. aripo densities. Indeed, T. aripo load on the non-preferred cultivar was lowest in subplots where the proportion of T. aripo-preferred cultivar was also low, while, and as expected, M. tanajoa load on the non-preferred cultivar showed decreasing trends with increasing T. aripo densities. The possible mechanisms by which cultivar mixing could increase predator load on the non-favourable cultivar were discussed. Our data showed that appropriate cultivar combinations effectively compensate for morphologically related differences in natural enemy abundance on a normally predator-deficient cultivar, resulting in lower pest densities on the non-favourable cultivar. In practical terms, this strategy could, in part, enhance adoption of cultivars that do not support sufficient levels of natural enemies for pest control.

Toxicity of neem oil to the cassava green mite Mononychellus tanajoa (Bondar) (Acari: Tetranychidae)

Neem ( Azadirachta indica A. Juss.)-derived pesticides have been used against a wide range of agricultural pests including tetranychid mites. Approaches combining lethal and sublethal toxicity studies of neem pesticides towards tetranychid mites are necessary to a comprehensive evaluation of such products. Here, we evaluated the lethal and sublethal toxicity of the neem oil Bioneem to the cassava green mite Mononychellus tanajoa (Bondar) by integrating lethal concentration (LC) with population growth and biological parameter studies. According to Probit analyses the concentration of neem oil Bioneem which kills 50% of the population (LC50) of M. tanajoa was 3.28 μL cm-2, which is roughly twice the field concentration recommended of this biopesticide to control pest mites (1.7 μL cm-2). The growth rate of the cassava green mite steadily decreased with dosages of neem oil. Furthermore, sublethal concentrations of the neem oil corresponding to the LC50 reduced the periods of the immature stages of M. tanajoa resulting in a shorter developmental time. Similarly, the number of eggs per day and the number of eggs per female per day, a proxy for fecundity, were drastically reduced in M. tanajoa females exposed to the LC50 of neem oil. Based on our comprehensive approach we conclude that the neem oil showed lethal as well as sublethal toxicity on growth rate and biological parameters such as duration of immature stages and fecundity of the cassava green mite M. tanajoa and it could be used as an ecological alternative for the management of this pest.

Comparative biology and growth rate of the mites Mononychellus tanajoa and Euseius ho (Acari) on cassava

The cassava green mite, Mononychellus tanajoa, is an important pest of cassava, Manihot esculenta (Euphorbiaceae), in the northeastern state of Maranhão, Brazil. Predatory mites of the family Phytoseiidae are key natural enemies of pest mites and are found inhabiting cassava plants. We compared some biological aspects and the growth rate of M. tanajoa and the generalist phytoseiid Euseius ho the most abundant predatory mite inhabiting cassava plants in the study region. All experiments were conducted in the laboratory on leaf discs of cassava leaves. The predatory mite was fed in all developmental stages with M. tanajoa. Euseius ho had lower periods of egg, larva, protonymph and deutonymph developmental periods, as well as the period from egg to adult compared to M. tanajoa. Furthermore, the predatory mite E. ho had a high instantaneous rate of increase (ri), yet lower than that observed for its prey, the cassava green mite M. tanajoa. The laboratory results suggest that the predatory mite E. ho may contribute to regulate populations of M. tanajoa in the field.

Interactions between the predatory mite Typhlodromalus aripo and the entomopathogenic fungus Neozygites tanajoae and consequences for the suppression of their shared prey/host Mononychellus tanajoa.

The predatory mite Typhlodromalus aripo and the entomopathogenic fungus Neozygites tanajoae, both introduced from Brazil for control of the cassava green mite (CGM) Mononychellus tanajoa, now co-occur in cassava fields in Benin. However, studies on interactions between these two natural enemies and how they might affect CGM biological control are lacking. We determined in screenhouse experiments the effects of single and combined releases of N. tanajoae and T. aripo on CGM suppression. In the single natural enemy treatment, both T. aripo and N. tanajoae significantly reduced CGM densities, but the results of the predator (T. aripo) are more quickly measurable than those of the pathogen (N. tanajoae) in our short-term experiment. The level of CGM suppression in the combined natural enemy treatment was reduced considerably compared with T. aripo-alone, but only slightly when compared with N. tanajoae alone, with a simultaneous reduction in T. aripo and N. tanajoae abundance or prevalence. In a laboratory experiment, T. aripo fed more on N. tanajoae-infected CGM than on healthy CGM and its oviposition and survival were reduced when fed on the former compared with the latter, which can help in explaining the reduction in numbers of T. aripo and consequently the considerable loss in suppression of CGM in the combined natural enemy treatment in the screenhouse experiment. Together, the screenhouse and the laboratory experiments predicted negative interactions between the two natural enemies with negative consequences for CGM biological control. Long-term field observations and rigorous field experiments that simultaneously manipulate T. aripo and N. tanajoae abundance and prevalence are needed to validate the prediction of this study.

The predatory mite Typhlodromalus aripo prefers green-mite induced plant odours from pubescent cassava varieties

It is well known that plant-inhabiting predators use herbivore-induced plant volatiles to locate herbivores being their prey. Much less known, however, is the phenomenon that genotypes of the same host plant species vary in the attractiveness of these induced chemical signals, whereas they also differ in characteristics that affect the predator’s foraging success, such as leaf pubescence. In a series of two-choice experiments (using a Y-tube olfactometer) we determined the preference of Typhlodromalus aripo for pubescent versus glabrous cassava cultivars infested with the cassava green mite Mononychellus tanajoa and also the preference for cultivars within each of the two groups. We found that when offered a choice between pubescent and glabrous cassava cultivars (either apex or leaves), T. aripo was significantly more attracted to pubescent cultivars. For each cultivar, M. tanajoa infested leaves and apices were equally attractive to T. aripo. There was however some variation in the response of T. aripo to M. tanajoa-infested plant parts within the group of pubescent cultivars, as well as within the group of glabrous cultivars. Our study confirms not only that T. aripo uses herbivore-induced plant volatiles to search for prey in cassava fields, but it also shows that it can discriminate between glabrous and pubescent cultivars and prefers the latter. This knowledge can be useful in selecting cultivars that are attractive and suitable to T. aripo, which, in turn, may promote biological control of the cassava green mite.

Effects of Ultraviolet Radiation on Predatory Mites and the Role of Refuges in Plant Structures

Most studies on ecological impact of solar ultraviolet (UV) radiation generally focus on plants. However, UV radiation can also affect organisms at other trophic levels. Protection against mortality induced by solar UV has, therefore, been hypothesized as one of the reasons why Typhlodromalus aripo hides in the apex of cassava plants during the day and comes out at night to prey on spider mites on leaves. In laboratory experiments using UV lamps, we determined the impact of UVA and UVB radiation on survival and oviposition of two leaf-inhabiting mites (Amblydromalus manihoti, Euseius fustis) and the apex-inhabiting mite (T. aripo), all three species being predators used for controlling the cassava green mite Mononychellus tanajoa in Africa. Whereas on leaf discs UVA has no negative impact on survival of the three predators, UVB is lethal to all of them. In contrast, nearly 85% of T. aripo survived after exposure to UVB inside apex of cassava plants. Exposure of A. manihoti and E. fustis to UVB radiation on the lower surface of a cassava leaf resulted in 36% survival. Oviposition and hatching of eggs laid after exposure to UVB were not affected, but eggs directly exposed to UVB did not hatch. Although caution should be exercised to extrapolate laboratory studies to the field, our results support the hypothesis that lower side of leaves, but especially plant apices, represent refuges that protect predatory mites from UVB. This might explain why T. aripo moves out of the apex to forage on leaves only during the night.

Within-Plant Migration of the Predatory Mite Typhlodromalus aripo from the Apex to the Leaves of Cassava: Response to Day–Night Cycle, Prey Location and Prey Density

Under attack by herbivores, plants produce a blend of “herbivore-induced plant volatiles (HIPV)” that help natural enemies of herbivores locating their prey, thereby helping plants to reduce damage from herbivory. The amount of HIPV emitted by plants increases with herbivore density and is positively correlated with the intensity of the olfactory response of natural enemies. In this study, we determined the effects of density or within-plant distribution of the herbivorous mite Mononychellus tanajoa on movement of the predatory mite Typhlodromalus aripo out of apices of cassava plants. Proportions of T. aripo that migrated out of apex, and distances traveled were significantly higher when M. tanajoa was further away from the apex—i.e. on middle or bottom leaves of cassava plants—than when present on top leaves, or absent from the plant. This supports previous field observations that T. aripo is not a sit-and-wait predator but uses HIPV to search and locate its prey within cassava plant.

Living at the threshold: Where does the neotropical phytoseiid mite Typhlodromalus aripo survive the dry season?

The establishment of the neotropical predatory mite Typhlodromalus aripo in sub-Saharan Africa has resulted in broadly successful biological control of the cassava green mite Mononychellus tanajoa throughout the cassava belt of Africa. In some mid-altitude areas and drier lowland savannahs of sub-Saharan Africa, which are characterized by cool or hot long (> or =5 months) dry seasons, the predator disappears from its habitat in the cassava apex during the dry season and reappears after the onset of rains. It is not known, however, where the predator remains during this time period. In this study, we conducted a field enclosure experiment of cassava plants with the objectives to determine if (a) T. aripo survives at very low densities in the apex, if (b) it survives in the soil or leaf litter below the cassava plant, and if (c) it recolonizes the cassava plant from the surrounding vegetation. Towards the end of the dry season, when the predators had disappeared from all cassava plants included in the experiment, five treatments were applied: (1) plants without enclosure; (2) plants with enclosure; (3) plants with enclosure, apices removed; (4) plants with enclosure, glue barrier around stem; and (5) plants kept free of T. aripo, without enclosure. Predator (re)appearance on cassava apices was monitored non-destructively at weekly intervals and was expressed as the proportion of plants with at least one apex with T. aripo per total number of plants of the treatment. The predators reappeared first on the plants of the treatments (1), (2), and (4). With a time lag of 7-8 weeks, the predators appeared also on the plants of the treatments (3) and (5). The time pattern of the predator's (re)appearance in the cassava apex of the different treatments suggests that (a) T. aripo survives the dry season in very low densities in the cassava apex; this result is supported by an assessment of the efficiency of non-destructive visual in-field apex inspections which proved that about 10% of the cassava apices that had T. aripo were not recognized as such; (b) T. aripo does not survive in the soil or leaf litter, but we did document cases in a screenhouse experiment, where few individuals migrated down to the ground and walked over exposed soil until they reached the apex bouquet traps; additionally, microclimate measurements in various cassava plant strata proved that the cassava apex and the cassava stem base are the locations with the highest relative humidity during the dry season--which makes the stem base a potentially interesting refuge; (c) T. aripo does not survive in the surrounding vegetation, which is supported by a vegetation survey, where T. aripo was not found on any other plant species than cassava.

Temporal and Spatial Dynamics of an Exotic Predatory Mite and Its Herbivorous Mite Prey on Cassava in Benin, West Africa

Abstract Quantitative knowledge of temporal and spatial distribution patterns of arthropod pests and their natural enemies is essential for understanding their interactions and is a prerequisite for the development of reliable sampling plans for estimating and monitoring pest and natural enemy abundance. Temporal and spatial distributions of the cassava green mite Mononychellus tanajoa (Bondar) (Acari: Tetranychidae) and its predator Typhlodromalus aripo DeLeon (Acari: Phytoseiidae) were determined in two cassava fields in Southern Benin, West Africa. Samples were taken to follow predator and prey dynamics at monthly intervals, from August 1998 (shortly after planting), to harvest time in June 1999. In addition, within-plant distribution of both predator and prey was determined in the upper 20 nodes of selected cassava plants on four occasions during the study period. In both field sites, temporal trends in abundance of M. tanajoa and T. aripo were similar but with a slight delay in T. aripo response to c...

Comparative life history traits of three neotropical phytoseiid mites maintained on plant-based diets

Abstract Plant-based foods may serve as alternative resources in meeting the nutritional requirements of predatory mites, when the preferred prey species is scarce. In laboratory studies, we evaluated the effect of various plant-based food resources associated with cassava on development and reproduction of Neoseiulus (= Amblyseius ) idaeus Denmark and Muma, Typhlodromalus manihoti Moraes, and Typhlodromalus aripo DeLeon, three predatory mites that have been used in classical biological control of the herbivorous mite Mononychellus tanajoa (Bondar) in Africa. The tests included five treatments (diets): pollen of three plant species— Zea mays L. (maize), of Leucaena leucocephala (Lam.) De Wit, and of Ricinus communis L.—cassava foliar exudate, and cassava leaf tissue (as the control). Neoseiulus idaeus did not complete development (hence no reproduction occurred) on any of the offered foods. Both T. aripo and T. manihoti successfully completed immature development—albeit in small proportions—on pollen of maize and L. leucocephala and on cassava foliar exudate. Only T. aripo completed immature development on pollen of R. communis and cassava leaf tissue; on the latter two foods, however, only males reached the adult stage. Moreover, of the five diets, none except pollen of maize was suitable for reproduction, and only for T. aripo , as T. manihoti did not reproduce on any of these diets. The duration of immature development of T. aripo was shorter on pollen of maize (6.9 days) than on cassava foliar exudate (11.1 days), while an intermediate value was recorded on pollen of L. leucocephala (8.6 days). Typhlodromalus manihoti developed faster on pollen of maize and cassava foliar exudate (6.8 days) than on pollen of L. leucocephala (9.8 days). Typhodromalus aripo lived much longer on pollen of maize and cassava foliar exudate compared with T. manihoti , whereas the two predator species had nearly similar female longevity on pollen of L. leucocephala . These results suggest that consumption of pollen of maize, pollen of L. leucocephala , or cassava foliar exudate can enhance development of T. aripo and T. manihoti in the absence of M. tanajoa , their preferred prey. Pollen of maize was suitable for T. aripo in completing oogenesis and hence allowing the predator to increase in abundance during shortages of M. tanajoa . The implications of our findings for the persistence of the acarine predator–prey system on cassava, and for the success of biological control of M. tanajoa in Africa are discussed.

Mites of cassava (Manihot esculenta crantz) habitats in Southern

This paper presents the first of a series of studies to evaluate the safety of a classical biological control program of the cassava green mite Mononychellus tanajoa (Bondar) (Acari: Tetranychidae) in Mozambique and Malawi involving the introduction of Typhlodromalus aripo DeLeon, a predatory mite of the family Phytoseiidae. The objective of this study was to determine the mite fauna of cassava and other common plant species in or around cassava fields in those countries. Twenty-one phytoseiid species were recorded in Mozambique and 32 in Malawi. On cassava, the dominant phytoseiids were Euseius baetae (Meyer and Rodrigues), Euseius bwende (Pritchard and Baker) and Typhlodromalus saltus (Denmark and Muma) in Mozambique, and Euseius fustis (Pritchard and Baker), Iphiseius degenerans (Berlese) and T. saltus in Malawi. On other plants, the dominant phytoseiids were E. baetae, Amblyseius sundi Pritchard and Baker and Paraphytoseius horrifer (Pritchard and Baker) in Mozambique, and I. degenerans, Euseius magucii (Meyer and Rodrigues) and Euseius orygmus (Ueckermann and Loots) in Malawi. Several of the most common plants associated with cassava were observed to harbor phytoseiid species that also were found on the latter. Those plants may be important as reservoirs of such predators when conditions are not suitable for them to live on cassava. This seemed to be particularly true for 6 phytoseiids in Mozambique (A. sundi, E. magucii, P. horrifer, Typhlodromalus spinosus (Meyer and Rodrigues), Typhlodromips shi (Pritchard and Baker) and Neoseiulus teke (Pritchard and Baker)), and 6 phytoseiids in Malawi (E. orygmus, Phytoseius amba Pritchard and Baker, T shi, Typhlodromus (Anthoseius) kikuyuensis Swirski and Ragusa, Typhlodromus (Anthoseius) malawiensis Zannou, Moraes and Hanna and N. teke), that were found on cassava at the end of the rainy season, but only on otherplants in the dry season. Mononychellus tanajoa was the dominant mite species on cassava in both countries in addition to the phytoseiids; few other species were found on that plant in either country. A larger diversity of mites in addition to phytoseiids was found on other plants, but always at low numbers. Phytoseiid diversity and abundance varied between savannah and forest zones. These variations are likely due to differences in biotic and abiotic factors between the two zones.

Seasonal cycles and persistence in an acarine predator‐prey system on cassava in Africa

AbstractWe applied time series analysis and a mechanistic predator‐prey model to long‐term data of monthly population counts of the herbivorous pest mite Mononychellus tanajoa and its introduced phytoseiid predator Typhlodromalus aripo from a cassava field in Benin, West Africa. In this approach, we determined the extent to which the main features of the observed predator‐prey fluctuations in cassava fields can be explained from biotic traits inherent to the biology of predator and prey, and the extent of the significance of abiotic factors in determining population levels. The time series analyses with cross‐correlation showed that the period of predator‐prey fluctuations coincided with the annual pattern of intense rainfall and onset of dry season. A pronounced M. tanajoa peak followed after a short lag (2 weeks) by a T. aripo peak coincided with a trough in rainfall intensity. Both the prey and predator had local and lower peaks that coincided with high rainfall intensity, but with a considerably longer lag (ca. 3 months) compared with the high peaks occurring at the onset of the dry season. Regression of log‐transformed data series (over a 7‐year period) showed that—except for the first year after predator release—M. tanajoa fluctuated around an almost time‐invariant mean population density, while T. aripo densities showed a consistent decline over the full observation period. To explain observed trends and periodic components in the data‐series of predator and prey densities, we review hypotheses that are based on (1) the annual patterns and trends in abiotic factors, (2) mechanisms endogenous to the predator‐prey system and (3) a combination of exogenous and endogenous factors.

Biological control of cassava green mite with exotic and indigenous phytoseiid predators—Effects of intraguild predation and supplementary food

Abstract Intraguild predation, one aspect of predator–predator interaction, has received in recent years increasingly greater attention because of mounting evidence of the impact of predator–predator interactions on the structure of ecological communities and biological pest control. In laboratory experiments, we determined if intraguild predation occurs between Typhlodromalus manihoti and Euseius fustis , two phytoseiid mite predators of the cassava green mite Mononychellus tanajoa on cassava in Africa, and if the level of intraguild predation is affected by the availability of the primary prey, M. tanajoa , and maize pollen as alternative non-prey food. In the laboratory, the two predators attacked and killed heterospecific larvae but they did so only when prey mites and alternative food (maize pollen) were absent or scarce. On a diet of intraguild prey alone, the two predator species survived for several days but failed to reproduce. Addition of abundant levels of M. tanajoa and maize pollen increased survival and reproduction of the two predator species and reduced intraguild predation to very low levels. We then determined, on whole plants in pot experiments in a screenhouse, the effect of maize pollen (an alternative food) on the interactions between the two predator species and the impact of predator–predator interactions on suppression of M. tanajoa population densities. In single predator species treatments, both E. fustis and T. manihoti significantly reduced M. tanajoa densities; but surprisingly, E. fustis appeared to be superior to T. manihoti . The co-presence of the two predators on the same cassava plant resulted in similar suppression of M. tanajoa population densities, but greater suppression of M. tanajoa compared with T. manihoti alone, regardless of presence or absence of maize pollen. The presence of the two predator species together reduced their respective abundance compared with single predator species treatments. Addition of maize pollen, however, significantly increased densities of the generalist predator E. fustis , in both single and two predator species treatments; and tilted the balance of the interactions between the two predator species in favour of E. fustis . The findings of our research underscore the role of generalist predators like E. fustis in the suppression of M. tanajoa populations on cassava, and the potential role of alternative non-prey food in altering the interactions between co-occurring predators sharing the same primary prey (by favouring the generalist predators), and the effect of these interactions on suppression of population densities of the shared primary prey.

Effect of cassava leaf harvest on a cassava green mite predator in the Democratic Republic of Congo

Typhlodromallus aripo, a predatory phytoseiid species of the cassava green mite Mononychellus tanajoa was introduced to the Democratic Republic of Congo in 1998. It established easily and spread quickly to other areas from the sites of first release. But its dispersal was constrained by intense consumption and trade of young tender cassava leaves, the natural habitat of the predator. A negative and significant correlation was found between the incidence of the harvest and the plants with T. aripo. Harvesting at 30, 45 and 60 days interval led to population densities of T. aripo for the entire production period of 1.823, 1.972 and 3.675 predators units per plant, respectively. For the check where no harvest was done, population density was 7.242 per plant. Significant differences, (P

Use of cell culture media for cultivation of the mite pathogenic fungi Neozygites tanajoae and Neozygites floridana

The pathogenic fungus Neozygites tanajoae, one of the most efficient natural enemies of the cassava green mite (CGM) Mononychellus tanajoa in Brazil, was introduced experimentally in Benin in 1998/1999 for the control of CGM. Isolation methods and culture media for in vitro production of N. tanajoae are reported for the first time in this study. Continuous growth of N. tanajoae was achieved using medium NT-1 (IPL-41 + 5–10% fetal bovine serum + 0.3% lactalbumin hydrolysate + 0.3% yeastolate). This medium supported production of N. tanajoae up to 1.53 (±0.08) × 10 7 hyphal bodies/mL after 8 days. The growth of N. tanajoae from Cruz das Almas, Brazil, was compared to the growth of two Neozygites floridana isolates with wider host ranges from North Carolina, US, and Palmira, Colombia, in 11 cell culture media. We demonstrated that differences in nutritional requirements exist between N. tanajoae and the similar species, N. floridana. N. tanajoae is a particularly fastidious species highly specific to CGM and grows well in few media while N. floridana which is less host specific, grows in a broader range of media, including serum free media. N. floridana isolates produced more than 2 × 10 6 hyphal bodies/mL in ⩾7 of the 11 media tested. However, the N. tanajoae isolate reached the same final concentration in only 3 media. Cell densities of N. tanajoae also increased slower than in N. floridana isolates in most media. N. tanajoae differed morphologically from the two N. floridana isolates in vitro. Hyphal bodies of eight N. tanajoae isolates are shorter than hyphal bodies of the two N. floridana isolates. The distinction of these two species was initially proposed based on host specificity, genetic and physiological patterns and is supported by the results presented in this study.

Infochemical-mediated niche use by the predatory mites Typhlodromalus manihoti and T. aripo (Acari: Phytoseiidae)

In Africa, Typhlodromalus manihoti and T. aripo, two introduced predators of the cassava green mite Mononychellus tanajoa, occupy different parts of cassava foliage. In the present study, niche use by these two predators, as mediated by prey-induced infochemicals, was investigated. In response to prey feeding damage, cassava plant parts emit volatile blends, that attract phytoseiidae predators. When given a choice between old cassava leaves infested with M. tanajoa and either apices or young cassava leaves infested with M. tanajoa, T. aripo displayed a marked preference for odors emitted from either infested apices or infested young leaves over infested old leaves but showed no preference for odors from apices versus young leaves, all infested with M. tanajoa. Typhlodromalus manihoti did not discriminate between volatiles from the three infested cassava plant parts. Our data show that T. aripo uses differences in volatile blends released by infested cassava plant parts and restricts its fundamental niche to a realized niche, which enables coexistence with its competitor T. manihoti.