Survival of Neozygites cf. floridana (Zygomycetes: Entomophthorales) in mummified cassava green mites and the viability of its primary conidia

The survival of Neozygites cf. floridana (Weiser and Muma) as dry hyphal bodies in mummified cassava green mites, Mononychellus tanajoa (Bondar), at 5.0% RH in the dark was affected by storage temperature. Survival of the fungus in mummies kept at 24±1.0°C could be demonstrated for 6–7 months. When stored at 4°C, the fungus sporulated from 90% of the mummies liberating an average of 186.9 primary conidia per mummy even after a storage period of 16 months, when the experiment was terminated. The temperature, humidity and light condition significantly affected the viability of primary conidia. The percent viability across all factors dropped from 98.4% after 0 h (beginning of the experiment) to 23.4% after a 1 h exposure to the conditions tested. Lower temperatures maintained higher viabilities with 86.3% of the conidia surviving after 18 h at 18°C, whereas almost all conidia died after 12 h at 33°C. Conidia survived less than 1 h when exposed to SDs (saturation deficit) of 2.0 mm Hg or higher at any tested temperature.     

Long-term preservation of Neozygites tanajoae (Entomophthorales: Neozygitaceae) in cadavers of Mononychellus tanajoae (Acari: Tetranychidae)

To determine the effect of storage on fungal survival, mummified cadavers of the cassava green mite pathogen, Neozygites tanajoae were placed at different conditions of temperature and relative humidity. The best condition for long-term preservation was ?10°C. At this condition, the fungus retained viability for 10 years when the experiment was terminated, with a decrease in sporulation with time. Cadavers placed at 4°C and 5% RH sporulated for 2 years, while the fungus survived for only 7 days at 25°C and 50% RH.     

Reproductive responses of Iphiseius degenerans and Neoseiulus teke (Acari: Phytoseiidae) to changes in the density of the cassava green mite, Mononychellus tanajoa (Acari: Tetranychidae)

We assessed the reproductive responses of adult female Iphiseius degenerans and Neoseiulus teke to increasing density of three stages of their prey, Mononychellus tanajoa, on cassava leaf discs under laboratory conditions. The oviposition rates increased with number of prey consumed per predator per day with a maximum of approximately two eggs per day for I. degenerans and four eggs per day for N. teke. The oviposition rate of N. teke was higher when consuming eggs than other prey stages. Neoseiulus teke was more efficient than I. degenerans in converting consumed prey into egg production. The data were adequately described by simple mathematical models.     

Functional responses of Iphiseius degenerans and Neoseiulus teke (Acari: Phytoseiidae) to changes in the density of the cassava green mite, Mononychellus tanajoa (Acari: Tetranychidae)

The functional responses of protonymph and adult female Iphiseius degenerans and Neoseiulus teke to increasing density of three stages of their prey, the cassava green mite (CGM), Mononychellus tanajoa, were studied on excised cassava leaf discs under laboratory conditions. The responses obtained were predominantly sigmoid type III curves with the highest plateau when both stages of I. degenerans and N. teke were preying on CGM eggs. In all cases, the predation rate of the former species exceeded that of the latter. The empirical data were fitted by four different models. From the models, the attack coefficient (a) and handling time (T _h) were estimated. For a given predator stage (protonymph or adult female), the predator's attack coefficient declines and handling time increases as the prey gets larger. For a given prey stage, the predator's attack coefficient increases and handling time decreases as the predator stage becomes larger.     

Effect of relative humidity and origin of isolates of Neozygites tanajoae (Zygomycetes: Entomophthorales) on production of conidia from cassava green mite, Mononychellus tanajoa (Acari: Tetranychidae), cadavers

Neozygites tanajoae is a very specialized fungus pathogenic to the cassava green mite (CGM), Mononychellus tanajoa, an important cassava pest introduced to Africa from the Neotropics. Conidial discharge from cadavers of CGM that died from infections with 14 isolates of N. tanajoae collected from diverse climates of Brazil was quantified to help select potential candidate strains for introduction to Africa. Studies aimed to identify isolates with lower requirements for relative humidity for sporulation and isolates that discharged more conidia during short periods of moisture. At 96 ± 0.5% RH, production of conidia was variable and even isolates from the Brazilian semi-arid region, e.g., Petrolina and Itaberaba, produced few conidia. Significant differences in the numbers of conidia produced by diverse Brazilian isolates were observed after 6, 9 and 12 h at 100% RH. At 100% RH, production of primary conidia increased considerably from an average of 57 ± 4 conidia at 6 h to 509 ± 37 conidia at 12 h. The isolate sporulating least (BIN21) discharged only 45.7% of the number of conidia produced by isolate BIN1, one of the isolates producing the most spores. Results from this study demonstrate that differences in production of conidia among isolates should be considered when selecting Neozygites isolates for new biological control introductions.     

An immunofluorescence study of mitosis in a mite-pathogen,Neozygites sp. (Zygomycetes: Entomophthorales)

Summary Mitosis in a mite-pathogenic species ofNeozygites (Zygomycetes: Entomophthorales) was investigated by indirect immunofluorescence microscopy using an antibody against -tubulin for visualization of microtubules (MTs). DAPI and rhodamine-conjugated phalloidin were used to stain chromatin and actin, respectively. Salient features of mitosis inNeozygites sp. are (1) a strong tendency for mitotic synchrony in any given cell, (2) conical protrusions at the poles of metaphase and anaphase nuclei revealed by actin staining, (3) absence of astral and other cytoplasmic MTs, (4) a spindle that occupies most of the nuclear volume at metaphase, (5) a spindle that remains symmetrical throughout most of mitosis, (6) kinetochore MTs that shorten during anaphase A, (7) a central spindle that elongates during anaphase B, pushing the daughter nuclei into the cell apices, and (8) interpolar MTs that continue to elongate even after separation of the daughter nuclei. Cortical cytoplasmic MTs are present in a few interphasic and post-cytokinetic cells. The data presented show thatNeozygites possesses features unique to this genus and support the erection of theNeozygitaceae as a separate family in theEntomophthorales.Abbreviations DAPI 4,6-diamidino-2-phenylindole - MT microtubule - SPB spindle pole body     

Importance of ambient saturation deficits in an epizootic of the fungus Neozygites floridana in cassava green mites (Mononychellus tanajoa)

The mite-pathogenic fungus Neozygites floridana Fisher (Entomophthorales: Neozygitaceae) is considered to have potential for the biological control of the cassava green mite, Mononychellus tanajoa (Bondar). However, its activity is sporadic and laboratory data suggest a strong dependence on night-time saturation deficits for transmission. We report on an epizootic of this fungus in a mite population in northeastern Brazil. During the epizootic, host populations appeared to be limited by a combination of the pathogen and a predatory mite Neoseiulus idaeus (Acari: Phytoseiidae). When temperatures increased, the epizootic finished and the host population began to grow. Abiotic conditions could not explain the variation in host mortality following pickup of infective propagules in this epizootic. However, night-time saturation did help to explain the variation in transmission from infective cadavers to newly killed hosts. This supports laboratory observations that horizontal transmission between hosts is determined mainly by saturation deficits, while the process of infection is little affected by abiotic conditions. A further field observation was the near-absence of resting spores in dead mites (ca. 0.1% of cadavers), suggesting that the pathogen population was unsuccessful in producing inoculum to infect future M. tanajoa populations. The implications are that this pathogen will only be effective as a biological control agent in periods of high relative humidity, and establishment in new areas may be limited by resting spore formation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Impact of natural epizootics of the fungal pathogen Neozygites floridana (Zygomycetes: Entomophthorales) on population dynamics of Tetranychus evansi (Acari: Tetranychidae) in tomato and nightshade

The tomato red spider mite, Tetranychus evansi (Acari: Tetranychidae) was recently introduced in Africa and Europe, where there is an increasing interest in using natural enemies to control this pest on solanaceous crops. Two promising candidates for the control of T. evansi were identified in South America, the fungal pathogen, Neozygites floridana and the predatory mite Phytoseiulus longipes. In this study, population dynamics of T. evansi and its natural enemies together with the influence of environmental conditions on these organisms were evaluated during four crop cycles in the field and in a protected environment on nightshade and tomato plants with and without application of chemical pesticides. N. floridana was the only natural enemy found associated with T. evansi in the four crop cycles under protected environment but only in the last crop cycle in the field. In the treatments where the fungus appeared, reduction of mite populations was drastic. N. floridana appeared in tomato plants even when the population density of T. evansi was relatively low (less than 10 mites/3.14 cm² of leaf area) and even at this low population density, the fungus maintained infection rates greater than 50%. The application of pesticides directly affected the fungus by delaying epizootic initiation and contributing to lower infection rates than unsprayed treatments. Rainfalls did not have an apparent impact on mite populations. These results indicate that the pathogenic fungus, N. floridana can play a significant role in the population dynamics of T. evansi, especially under protected environment, and has the potential to control this pest in classical biological control programs.     

Neozygites abacaridis sp. nov. (Entomophthorales), a new pathogen of phytophagous mites (Acari,Eriophyidae)

A new entomopathogenic fungus, described here as Neozygites abacaridis n. sp. (Zygomycetes: Entomophthorales), has been found on the mites Abacarus hystrix, Aculodes dubius, and A. mckenziei (Acari: Eriophyidae). It differs from other Neozygites species affecting mites by its small, globose primary conidia, short-ovoid, smoky coloured capilliconidia, and very short capillary conidiophores-which are usually not longer than the spore length. This pathogen infected mite individuals in autumn (from mid-August until mid-November) on Lolium perenne, Agrostis stolonifera, and Festuca rubra. It caused 0.5-1% host's mortality in the vicinity of Siedlce (Eastern Poland) and up to 2-8%, on an average in Puszczykowo (Wielkopolski National Park near Poznań), where its prevalence on some plants reached 13%.     

The effect of host plants on Tetranychus evansi, Tetranychus urticae (Acari: Tetranychidae) and on their fungal pathogen Neozygites floridana (Entomophthorales: Neozygitaceae)

In a series of tritrophic-level interaction experiments, the effect of selected host plants of the spider mites, Tetranychus evansi and Tetranychus urticae, on Neozygites floridana was studied by evaluating the attachment of capilliconidia, presence of hyphal bodies in the infected mites, mortality from fungal infection, mummification and sporulation from fungus-killed mite cadavers. Host plants tested for T. evansi were tomato, cherry tomato, eggplant, nightshade, and pepper while host plants tested for T. urticae were strawberry, jack bean, cotton and Gerbera. Oviposition rate of the mites on each plant was determined to infer host plant suitability while host-switching determined antibiosis effect on fungal activity. T. evansi had a high oviposition on eggplant, tomato and nightshade but not on cherry tomato and pepper. T. urticae on jack bean resulted in a higher oviposition than on strawberry, cotton and Gerbera. Attachment of capilliconidia to the T. evansi body, presence of hyphal bodies in infected T. evansi and mortality from fungal infection were significantly higher on pepper, nightshade and tomato. The highest level of T. evansi mummification was observed on tomato. T. evansi cadavers from tomato and eggplant produced more primary conidia than those from cherry tomato, nightshade and pepper. Switching N. floridana infected T. evansi from one of five Solanaceous host plants to tomato had no prominent effect on N. floridana performance. For T. urticae, strawberry and jack bean provided the best N. floridana performance when considering all measured parameters. Strawberry also had the highest primary conidia production. This study shows that performance of N. floridana can vary with host plants and may be an important factor for the development of N. floridana epizootics.     

Pathogenicity and specificity of Neozygites tanajoae and Neozygites floridana (Zygomycetes: Entomophthorales) isolates pathogenic to the cassava green mite

The cassava green mite (CGM), Mononychellus tanajoa, a native of South America was accidentally introduced into Africa where it causes serious crop losses. The possibility of introducing classical biological agents from the native home of CGM into Africa was investigated. Thus, we conducted a series of laboratory assays of the native fungal pathogens, Neozygites tanajoae from Brazil and Neozygites floridana from Colombia and Brazil, and compared them with N. tanajoae isolates from Benin. Infectivity of both fungal species, was assayed against the twospotted spider mite, Tetranychus urticae, and against the red mite, Oligonychus gossypii. Pathogenicity against CGM and host range studies were conducted by transferring adult females of each mite species to leaf discs containing sporulated cadavers with a halo of conidia of each fungal isolate. All isolates caused some degree of infectivity to CGM. None of the isolates of N. floridana and N. tanajoae tested were pathogenic to O. gossypii, and only two isolates infected T. urticae. Most isolates from Brazil were highly virulent and infected only CGM. Sixteen N. tanajoae isolates caused more than 89% mortality and more than 62% of the CGM became mummified. A mummified CGM is characteristically a swollen, brown fungus-killed mite that has great potential to produce conidia. However, high mortality was not always associated with high mummification. The median mummification time ranged from 4.4 to 6.7 days. Five Brazilian isolates caused >75% mummification with a median mummification time <5 days. Isolates that cause high mummification in a short period of time would be more likely to cause epizootics and to establish in the new environment. Therefore, these isolates would be the best candidates for introduction to Africa.     

Intraspecific diversity of the Cassava Green Mite Mononychellus progresivus (Acari: Tetranychidae) using comparisons of mitochondrial and nuclear ribosomal DNA sequences and cross-breeding

Intraspecific diversity in Cassava Green Mite Mononychellus progresivus Doreste was examined using individuals collected in Benin and the Congo and in Columbia and Brazil. Comparisons were based on mitochondrial and ribosomal DNA sequences and the results of several cross-breeding experiments. Sequence variation was examined in a total of 1139 base pairs (bp) constituting the ITS2 ribosomal DNA (805 bp) and a fragment of the Cytochrome Oxidase I (COI) gene (334 bp). Sequence divergence is low, ranging from 0% to 2.1% for COI and from 0% to 0.4% for ITS2. Inter-strain comparisons have shown that the two African populations appear to be identical. They were similar to the Colombian population while the Brazilian population was clearly different. The data support the hypothesis of a single introduction of the species in the two African populations. Crossing experiments have shown partial hybrid sterility, suggesting a genetic incompatibility consistent with differences detected by sequence data. The results show the usefulness of molecular markers as a tool for determining taxonomic status and dispersion paths in spider mites.     

Effect of cassava exudate and prey densities on the survival and reproduction of Typhlodromalus limonicus (Garman & McGregor) s.l. (Acari: Phytoseiidae), a predator of the cassava green mite,Mononychellus tanajoa (Bondar) (Acari: Tetranychidae)

The effects of cassava exudate and prey densities on reproduction and survival of the predatory mite, Typhlodromalus limonicus (Garman & McGregor) (Acari: Phytoseiidae), were investigated in the laboratory. Females were provided either cassava exudate ad lib. daily, low or high numbers of the cassava green mite prey, Mononychellus tanajoa (Bondar) (Acari: Tetranychidae) daily, or exudate for 5 or 10 days before switching to a low or high prey diet. Females fed only exudate laid no eggs. Females fed exudate before prey experienced a significant decrease (30%) in the number of eggs laid compared to females fed high numbers of prey daily. The reduction in fecundity was the result of prolonged preoviposition periods (2.0 days on prey daily vs 4.0 days on exudate before prey) and reduced number of eggs laid per female per day (1.7 eggs per female per day on prey daily vs 0.4 eggs per female per day on exudate before prey). Females fed only exudate had a greater survival rate and longevity than females fed prey daily or females fed exudate before a diet of prey. These results suggest that T. limonicus can survice for a limited period on cassava exudate during periods of low prey availability, but requires prey to complete oögenesis and propagate the population.     

Interactions of two natural enemies of Tetranychus evansi, the fungal pathogen Neozygites floridana (Zygomycetes: Entomophthorales) and the predatory mite, Phytoseiulus longipes (Acari: Phytoseiidae)

Tetranychus evansi is an exotic pest of Solanaceous crops in Africa discovered in Zimbabwe in 1979. Two natural enemies, the predatory mite Phytoseiulus longipes and the fungal pathogen Neozygites floridana are important causes of mortality in T. evansi populations in Brazil. The first part of this study assessed the effects of N. floridana on predation and oviposition of P. longipes fed on N. floridana infected T. evansi and T. urticae. No N. floridana hyphal bodies were found in P. longipes after this feeding, demonstrating that N. floridana is not pathogenic to P. longipes and does not affect its oviposition. The second part of the study investigated the time spent on searching for and consuming of eggs on leaf discs with and without N. floridana capilliconidia. Both the searching and the feeding time on the first egg were similar on leaf discs with and without capilliconidia. When P. longipes was offered the choice of feeding on eggs on leaf discs with or without capilliconidia, the numbers of eggs consumed were not different. The only N. floridana effect observed on P. longipes was reduced egg predation. In addition, increased time spent grooming on leaf discs with capilliconidia was observed. P. longipes was efficient in removing most capilliconidia attached to the body through self-grooming behavior. This suggests that although the predator did not avoid areas with capilliconidia, it detected and removed most capilliconidia attached to the body. Increased grooming may account for the lower egg predation rates.     

Scaling up tests on virulence of the cassava green mite fungal pathogen <Emphasis Type="Italic">Neozygites tanajoae</Emphasis> (Entomophthorales: Neozygitaceae) under controlled conditions: first observations at the population level

Virulence of entomopathogens is often measured at the individual level using a single host individual or a group of host individuals. To what extent these virulence assessments reflect the impact of an entomopathogen on their host in the field remains largely untested, however. A methodology was developed to induce epizootics of the cassava green mite fungal pathogen Neozygites tanajoae under controlled conditions to evaluate population-level virulence of two (one Beninese and one Brazilian) isolates of the entomopathogen—which had shown similar individual-level virulence but different field impacts. In unrepeated separate experiments we inoculated mite-infested potted cassava plants with either 50 or 25 live mites (high and low inoculum) previously exposed to spores of N. tanajoae and monitored the development of fungal infections for each isolate under the same conditions. Both isolates caused mite infections and an associated decline in host mite populations relative to the control (without fungus) in all experiments, but prevalence of the fungus varied with isolate and increased with inoculum density. Peak infection levels were 90% for the Beninese isolate and 36% for the Brazilian isolate at high inoculum density, and respectively 17% and 25% at low inoculum density. We also measured dispersal from inoculated plants and found that spore dispersal increased with host infection levels, independent of host densities, whereas mite dispersal varied between isolates. These results demonstrate that epizootiology of N. tanajoae can be studied under controlled conditions and suggest that virulence tests at the population level may help to better predict performance of fungal isolates than individual-level tests.     

Effect of some food sources associated with cassava in Africa on the development, fecundity and longevity of Euseius fustis (Pritchard and Baker) (Acari: Phytoseiidae)

Various foods associated with cassava were tested for their effect on the development, fecundity and longevity of Euseius fustis, the most common phytoseiid species found on cassava in Africa. Euseius fustis developed successfully to adulthood on the spider mite prey species Mononychellus tanajoa (Bondar) and Oligonychus gossypii (Zacher) and on pollen from maize, castor bean and cassava. Euseius fustis also completed development on water-diluted phloem exudate from cassava, diluted honeydew from the cassava mealybug and on various pollen and prey combinations. When reared on Tetranychus urticae Koch prey or free water only, E. fustis did not develop past the deutonymphal stage. All larvae held on clean leaf discs on water-soaked cotton died without moulting, suggesting that E. fustis must feed in order to moult to the nymphal stages. Diets of maize plus castor bean pollen and maize pollen plus M. tanajoa resulted in the highest rate of development, the highest fecundity and the greatest longevity. Castor bean pollen alone and maize pollen alone produced a higher fecundity and greater longevity than M. tanajoa tested alone. A colony of E. fustis reared continuously for seven generations on castor bean pollen produced nine times more adult females than a colony of E. fustis reared continuously on M. tanajoa. No negative effects on the development and fecundity of E. fustis were observed after seven generations were reared on pollen.     

不同温度、土壤含水量及日光照时数对棉露尾甲虫(Haptoncus luteolus (Erichson))生长发育的影响

在5,10,15,20,30℃等5种温度、10%,20%,30%等3种土壤含水量和8,12,16h等3种日光照时数共45个处理组合条件下,以丝瓜花作为饲料研究了3个因素对棉露尾甲生长发育的联合作用。结果表明:适合于卵生长发育的处理组合为25～35℃、10～15%和12～16h,其中最佳处理组合为30℃、10%和12h,在此组合条件下,卵发育历期为0.8d,孵化率为93.3%;适合于幼虫及蛹生长发育的处理组合为:25～30℃、10～15%和12～16h,其中最佳处理组合分别为30℃、10%、12h和30℃、10%、8h,在此组合条件下,幼虫历期、存活率和蛹历期、羽化率分别为5.0d、85.7%和2.2d、83.3%。在三元二次回归模型中,卵、幼虫、蛹和整个未成熟期(卵至蛹的历期)发育进度最快时的处理组合分别为27.5℃、10%、8h,30℃、20%、12h,32.5℃、10%、16h和30℃、10%、16h;此时理论最短历期分别为0.8、4.4、1.4d和7.3d。     

Altered behavior and distribution of pea aphids, Acyrthosiphon pisum (Homoptera: Aphididae), infected with Pandora neoaphidis (Zygomycetes: Entomophthorales)

The distribution and mobility of infected aphid hosts can have a great effect on the ability of a pathogen to spread throughout a population. The distribution of dead and living pea aphids (Acyrthosiphon pisum) infected with Pandora neoaphidis was compared with that of their healthy conspecifics. Infected aphids were significantly more likely to be found on the undersides of alfalfa leaves and off of the plants than were healthy aphids. These two shifts in microhabitat location have potential costs and benefits for both the host and the pathogen.     

Prey-related odor preference of the predatory mites Typhlodromalus manihoti and Typhlodromalus aripo (Acari: Phytoseiidae)

Typhlodromalus manihoti and Typhlodromalus aripo are exotic predators of the cassava green mite Mononychellus tanajoa in Africa. In an earlier paper, we showed that the two predators were attracted to odors from M. tanajoa-infested cassava leaves. In addition to the key prey species, M. tanajoa, two alternative prey mite species, Oligonychus ossypii and Tetranychus urticae also occur in the cassava agroecosystem. Here, we used a Y-tube olfactometer to determine the attraction of the predators to odors from O. gossypii- or T. urticae-infested cassava leaves and their prey-related odor preference. T. aripo but not T. manihoti was slightly attracted to odors from O. gossypii-infested leaves. Both predator species showed a stronger response to odors from cassava leaves infested by M. tanajoa over odors from cassava leaves infested by O. gossypii. Neither predator species was attracted to odors from T. urticae-infested leaves and the predators preferred the odors from M. tanajoa-infested leaves over those from T. urticae-infested leaves. When O. gossypii was present together with M. tanajoa on the same leaves or on different sets of leaves offered together as an odor source the two predators were attracted. In contrast, after mixing non-attractive odors from T. urticae-infested leaves with attractive odors from M. tanajoa-infested leaves, neither T. aripo nor T. manihoti was attracted. Ecological advantages and disadvantages of the predators’ behavior and possible implications for biological control of M. tanajoa are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of temperature and relative humidity on the rate of development,fecundity and life table parameters of the red spider mite Oligonychus mangiferus (Rahman and Sapra) (Acari: Tetranychidae)

Studies on biology of Oligonychus mangiferus (Rahman and Sapra) at combination of eight constant temperatures and relative humidities (RHs) viz., 7.0°C with 85% RH, 10°C with 80% RH, 15.0°C with 75% RH, 23.0°C with 70% RH, 31.0°C with 65% RH, 34.0°C with 65% RH, 36.0°C with 60% RH and 40.0°C with 55% RH revealed that the optimal condition for the development of these mites are 15.0–31.0°C and 65–75% RH. The highest temperature and the lowest RH accelerated the rate of development and induced more reproduction of O. mangiferus. Its population also multiplied 30.81 times in a generation time of 27.36 days at 31.0°C and 65% RH, while the same population only increased 7.46 times in a generation time of 48.07 days at 15.0°C and 75% RH. Fecundity was highest at 31.0°C and 65% RH with 46.43 eggs per female. The highest intrinsic rate of natural increase was observed at 31.0°C as 0.125 per day.