This is the fifth publication in a series to determine the phytoseiid mites of sub-Saharan Africa... more This is the fifth publication in a series to determine the phytoseiid mites of sub-Saharan Africa. Thirty-one phytoseiid species of the subtribe Amblyseiina are reported in this paper. They refer to all species of this subtribe known to occur in sub-Saharan Africa. Ten of these species are described for the first time, 15 species are redescribed and 6 are not evaluated in this study. Most of those species were collected in cassava habitat in tropical Africa and in other habitats in South Africa. A key is included to help in the separation of these species.
FIGURE 13. Typhlodromus (Anthoseius) daresalaami El-Banhawy & Abou-Awad (female): A. Dorsal shiel... more FIGURE 13. Typhlodromus (Anthoseius) daresalaami El-Banhawy & Abou-Awad (female): A. Dorsal shield; B. Ventral surface; C. Spermatheca; D. Leg IV.
FIGURE 1. Typhlodromus (Anthoseius) acaciae Schultz: Female—A. Dorsal shield; B. Ventral surface;... more FIGURE 1. Typhlodromus (Anthoseius) acaciae Schultz: Female—A. Dorsal shield; B. Ventral surface; C. Chelicera; D. Spermatheca; E. Leg IV; Male—F. Spermatodactyl; G. Ventrianal shield.
The effects of prey mite suitability on several demographic characteristics of phytoseiid predato... more The effects of prey mite suitability on several demographic characteristics of phytoseiid predators and the relationship of these effects to the potential of phytoseiid predators to control herbivorous mite populations are well documented. Evidence has also accumulated in the last 20 years demonstrating that phytoseiid predators utilize herbivorous prey mite-induced plant volatiles as olfactory cues in locating their herbivorous mite prey, but less well established is the predictability of reproductive success from the ability of the predators to utilize olfactory cues to locate their prey, and how these processes are related to the success of the predators as biological control agents of the herbivorous mite. In this study, we determined in laboratory no choice experiments, the development, survivorship and fecundity of the two neotropical phytoseiid predators Typhlodromalus manihoti Moraes and T. aripo DeLeon when feeding on three herbivorous mites, including the key prey species Mononychellus tanajoa (Bondar), and the two alternative prey species Oligonychus gossypii (Zacher) and Tetranychus urticae (Koch). Intrinsic rate of increase (r m) of T. aripo was 2.1 fold higher on M. tanajoa as prey compared with T. urticae as prey, while it was almost nil on O. gossypii. For T. manihoti, r m was 2.3 fold higher on M. tanajoa as prey compared with O. gossypii as prey, while reproduction was nil on T. urticae. An independent experiment on odor-related prey preference of the two predator species (Gnanvossou et al. 2002) showed that T. manihoti and T. aripo preferred odors from M. tanajoa-infested leaves to odors from O. gossypii-infested leaves. Moreover, both predator species preferred odors from M. tanajoa-infested leaves over those from T. urticae-infested leaves. As reported here, life history of the two predatory mites matches odor-related prey preference if the key prey species is compared to the two inferior prey species. The implications of our findings for the persistence of T. manihoti and T. aripo and biological control of M. tanajoa in the cassava agroecosystem in Africa are discussed.
Plant-based foods may serve as alternative resources in meeting the nutritional requirements of p... more 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
New cassava varieties were developed by IITA in order to improve their agronomic yield, pest and ... more New cassava varieties were developed by IITA in order to improve their agronomic yield, pest and disease resistance, and micronutrient content (higher beta-carotene and other carotenoids). This study assessed the ability of 18 new released varieties to produce a traditional cassava food product named “bâton de manioc” in Cameroon central region, in order to maximize their chances of adoption by processors and consumers. Bâton is a steamed cassava mash wrapped in leaves of Megaphrynium macrostachyum, or leaves of other species of Marantaceae. The successive steps of the traditional process were described in details and data on processing yields, material balances, shaping and cooking conditions, as well as production capacity and product quality, were reported. Results showed that “bâton” with both better quality and productivity were obtained from varieties with lower fibre content and larger size of roots. The best profitability was obtained with varieties longer than 25 cm, with a diameter comprised between 6 and 9 cm and a weight comprised between 0.8 and 1.4 kg. Additionally, a survey with processors highlighted the desired quality criteria for cassava varieties to make a good “bâton”. Eight varieties out of the 18 were finally identified as able to be processed into a good “bâton”. Their acceptability by a large number of Cameroonian consumers will be tested in a further study. Beyond these initial results, the originality of the approach was to assess performance and quality criteria for cassava processing in local conditions, which appears very effective to ensure that improved varieties have appropriate characteristics for traditional uses, and also to integrate market and consumers' demands early in varietal improvement programs. (Resume d'auteur)
Two countrywide surveys were conducted in April-May and May-June 2004 throughout the cassava grow... more Two countrywide surveys were conducted in April-May and May-June 2004 throughout the cassava growing belt of Mozambique including several provinces: Gaza, Inhambane, Sofala, Manica, Zambezia, Nampula and Cabo Delgado. Both surveys were planned to assess the distribution, incidence and damage severity of diseases and pests that affect cassava production in Mozambique. Using the methodology developed by the International Institute of Tropical Agriculture (IITA), 202 and 175 cassava fields between 4-8 months old were sampled for pests and diseases in April-May 2003 and May-June 2004, respectively. The results of both surveys showed in the case of diseases that cassava mosaic disease (CMD) was found to be the most widespread disease in Mozambique although the distribution, incidence, and severity varied among provinces, among fields and within fields. The most severe damage was recorded in Gaza, Sofala and Nampula where the average scores were above 3 on a 1-5 damage scale but only in a limited number of sample fields. In other provinces, the disease was either absent or damage symptoms were slight to moderate (2-3). The DNA analysis of the leaf samples coIlected in 2004 throughout the country revealed the presence of several strains of CMD virus including, the African Cassava Mosaic Virus (ACMV), the Eastern African Cassava Mosaic Virus (EACMV), and a combination of both African and EastAfrican Cassava Mosaic Virus (ACMV+EACMV) in 80.5% and 7.6% of the field samples respectiveIy. The devastating East African Cassava Mosaic Virus - Ugandan Strain (EACMVUG2) was absent from all sampled fields. The presence of cassava brown streak disease (CBSD) was confirmed as a serious threat particularly in two of the three Northern provinces of Zambezia and Nampula and at lesser extent in Cabo Delgado. However, the severity was the highest in Zambezia and in the district of Nakala in Nampula province. The other known common tropical diseases of cassava such as the cassava bacterial blight (CBB) and cassava anthracnose disease (CAD) were of minor importance. The cassava green mite (CGM), Mononychellus tanajoa Bondar remained a problem in the southern provinces (Gaza, Inhambane) where the exotic predatory mites Typhlodromalus aripo De Leon was not yet established.. CGM infestations were followed by whitefly (WF) infestations in a rank-order hierarchy of infestation rates. Although generally known as vectors of the cassava mosaic disease (CMD), the high whitefly population densities recorded in some locations (>lo0 adults per plant, e.g. in Zambezia province), was considered a direct pest causing considerable leaf damage and covering plants with sooty molds. The incidence and damage severity of other common pests of cassava (i.e. cassava mealybug, termites, and grasshoppers) appeared insignificant
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Two new mite species of the family Phytoseiidae (Acari: Mesostigmata), Neoseiulus yanineki sp. no... more Two new mite species of the family Phytoseiidae (Acari: Mesostigmata), Neoseiulus yanineki sp. nov. and Typhlodromips cameroonensis sp. nov., are described from Cameroon, Central Africa.
This is the fourth publication of a series to determine the phytoseiid mites of sub-Saharan Afric... more This is the fourth publication of a series to determine the phytoseiid mites of sub-Saharan Africa. Twenty-six phytoseiid species of the subtribes Arrenoseiina Chant & McMurtry (5 species) and Proprioseiopsina Chant & McMurtry (9 species), and tribe Typhlodromipsini Chant & McMurtry (12 species), are reported in this paper. They refer to all species of these taxa known to occur in sub-Saharan Africa. Eight of these species are described for the first time, 14 species are redescribed and 4 are not evaluated in this study. Most of those species were collected in cassava habitat in tropical Africa and in other habitats in South Africa. Keys are included to help in the separation of the species in each tribe or subtribe.
the Centre de Coopération Internationale en Recherche Agronomique pour le Développement (CIRAD), ... more the Centre de Coopération Internationale en Recherche Agronomique pour le Développement (CIRAD), that includes a growing number of research and development partners. RTB brings together research on its mandate crops: bananas and plantains, cassava, potato, sweetpotato, yams, and minor roots and tubers, to improve nutrition and food security and foster greater gender equity especially among some of the world's poorest and most vulnerable populations.
International journal of pest management, Oct 29, 2015
The cotton aphid (Aphis gossypii) is one of the major pests of okra. Eleven okra varieties collec... more The cotton aphid (Aphis gossypii) is one of the major pests of okra. Eleven okra varieties collected from farmers' fields in Cameroon and four aphid-resistant accessions from The World Vegetable Center (AVRDC, Asian Vegetable Research and Development Center) were evaluated from October 2012 to March 2013, and another seven aphid-resistant accessions from AVRDC were evaluated from March to July 2013 at AVRDC's Nkolbisson station, Yaoundé, Cameroon. Accessions selected from these trials were screened in an advanced confirmatory screening in autumn (October–December) 2013 in Shanhua, Taiwan. Results showed that none of the farmers' landraces were resistant to aphids. Two accessions (VI041210 and VI033824) with the lowest aphid populations had the highest trichome density. Analysis of various phytochemicals in selected okra accessions revealed that higher nitrogen and potassium levels made the okra accessions susceptible to aphids during the reproductive stage of the plants. Similarly, the total phenol content was lower in moderately resistant accessions during their reproductive stage. Aphid feeding induced an increase in phenols, and to a lesser extent, tannins. Accessions VI041210 and VI033824 could be incorporated into an integrated pest management strategy to enhance productivity of okra.
Diachasmimorpha longicaudata (Ashmead), a solitary koinobiont larval–prepupal endoparasitoid of f... more Diachasmimorpha longicaudata (Ashmead), a solitary koinobiont larval–prepupal endoparasitoid of fruit flies, was introduced into Kenya for testing and final release against the recently discovered invasive species, Bactrocera invadens Drew, Tsuruta and White in Africa. Laboratory experiments were conducted to determine host preference, host acceptability for oviposition and physiological suitability of B. invadens and five other indigenous tephritid fruit fly species –Ceratitis capitata (Wiedemann), Ceratitis cosyra (Walker), Ceratitis rosa Karsch, Ceratitis fasciventris (Bezzi) and Ceratitis anonae Graham – for the development of D. longicaudata. Females of D. longicaudata visited all host‐larval patches, and were also attracted to these hosts at comparable levels. Acceptability, successful development of parasitoid progenies and their sex ratio varied widely across hosts. C. capitata yielded the highest parasitoid numbers whereas B. invadens was the only host that yielded a female‐biased sex ratio. Larvae of B. invadens, C. rosa, C. fasciventris and C. anonae mounted differential immune reaction towards D. longicaudata eggs. Although, the parasitoid performed poorly on the target host B. invadens, it was able to form new association with C. cosyra and C. capitata. The prospect of using this parasitoid in biological control of African indigenous fruit flies is discussed.
Entomologia Experimentalis Et Applicata, May 22, 2003
Experimental and correlative evidence has steadily mounted over the past 30 years implicating spi... more Experimental and correlative evidence has steadily mounted over the past 30 years implicating spiders in the suppression of insect herbivore pests in crop fields. A large body of evidence has also shown that increasing agroecosystem vegetation diversity often influences the abundance of herbivores and their natural enemies. In previous experiments, the abundance of several species of spiders on grapevines in a raisin grape vineyard was twofold enhanced in vineyard plots vegetationally diversified with a cover crop. A concomitant reduction in the abundance of the leafhopper pest Erythroneura variabilis Beamer was observed on grapevines in the diversified plots, but a causal relationship was not established. In the present study, we simultaneously manipulated spider densities (in open-vine spider exclusion and vine-shoot enclosures) and ground cover to determine their relative impact on E. variabilis population dynamics. Open-vine spider exclusion resulted in an average 35% increase in the density of E. variabilis the greatest effect with occurring during the first and second leafhopper generations. The negative impact of spiders on E. variabilis densities was corroborated with vineshoot enclosure experiments. Under the conditions of the present study, the cover crop per se did not affect the dynamics of E. variabilis populations on grapevines, despite a 1.6-fold increase in spider densities on vines in cover crop plots, compared with vines in bare ground plots, probably due to insufficient spider enhancement and low overall E. variabilis abundance during the summer months. The cover crop had little effect on vine macronutrient status (and presumably vine water status). While this study provided further support for the hypothesis that vegetation diversity can enhance spider abundance, this enhancement does not always lead to lower pest densities, thus underscoring the complexity and variability that exists in interactions involving cover crop, spiders, and crop plants and their herbivore pests.
When predation risk varies in space and time and with predator species, successful prey defence r... more When predation risk varies in space and time and with predator species, successful prey defence requires specific responses to each predator. In cassava fields in Africa, the herbivorous cassava green mite (Mononychellus tanajoa) is attacked by three predatory mite species that are segregated within the plant: the leaf-dwelling Typhlodromalus manihoti and Euseius fustis occur on the middle leaves, whereas the apex-inhabiting T. aripo migrates from the apex to the top leaves only during the night. We found that differential distributions of these predators allow prey to escape predation by vertical migration to other plant strata. We studied the role of odours in the underlying prey behaviour on predator-free plants placed downwind from plants with predators and prey or with prey only. Prey showed increased vertical migration in response to predator-related odours. Moreover, these responses were specific: when exposed to odours associated with T. manihoti, prey migrated upwards, irrespective of the plant stratum where they were placed. Odours associated with T. aripo triggered a flexible response: prey on the top leaves migrated downwards, whereas prey on the middle leaves migrated upwards. Odours associated with E. fustis, a low-risk predator, did not elicit vertical migration. Further experiments revealed that: (1) prey migrate up or down depending on the stratum where they are located, and (2) prey discrimination among predators is based upon the perception of predator species-specific body odours. Thus, at the scale of a single plant, odour-based enemy specification allows herbivorous mites to escape predation by vertical migration.
This is the fifth publication in a series to determine the phytoseiid mites of sub-Saharan Africa... more This is the fifth publication in a series to determine the phytoseiid mites of sub-Saharan Africa. Thirty-one phytoseiid species of the subtribe Amblyseiina are reported in this paper. They refer to all species of this subtribe known to occur in sub-Saharan Africa. Ten of these species are described for the first time, 15 species are redescribed and 6 are not evaluated in this study. Most of those species were collected in cassava habitat in tropical Africa and in other habitats in South Africa. A key is included to help in the separation of these species.
FIGURE 13. Typhlodromus (Anthoseius) daresalaami El-Banhawy & Abou-Awad (female): A. Dorsal shiel... more FIGURE 13. Typhlodromus (Anthoseius) daresalaami El-Banhawy & Abou-Awad (female): A. Dorsal shield; B. Ventral surface; C. Spermatheca; D. Leg IV.
FIGURE 1. Typhlodromus (Anthoseius) acaciae Schultz: Female—A. Dorsal shield; B. Ventral surface;... more FIGURE 1. Typhlodromus (Anthoseius) acaciae Schultz: Female—A. Dorsal shield; B. Ventral surface; C. Chelicera; D. Spermatheca; E. Leg IV; Male—F. Spermatodactyl; G. Ventrianal shield.
The effects of prey mite suitability on several demographic characteristics of phytoseiid predato... more The effects of prey mite suitability on several demographic characteristics of phytoseiid predators and the relationship of these effects to the potential of phytoseiid predators to control herbivorous mite populations are well documented. Evidence has also accumulated in the last 20 years demonstrating that phytoseiid predators utilize herbivorous prey mite-induced plant volatiles as olfactory cues in locating their herbivorous mite prey, but less well established is the predictability of reproductive success from the ability of the predators to utilize olfactory cues to locate their prey, and how these processes are related to the success of the predators as biological control agents of the herbivorous mite. In this study, we determined in laboratory no choice experiments, the development, survivorship and fecundity of the two neotropical phytoseiid predators Typhlodromalus manihoti Moraes and T. aripo DeLeon when feeding on three herbivorous mites, including the key prey species Mononychellus tanajoa (Bondar), and the two alternative prey species Oligonychus gossypii (Zacher) and Tetranychus urticae (Koch). Intrinsic rate of increase (r m) of T. aripo was 2.1 fold higher on M. tanajoa as prey compared with T. urticae as prey, while it was almost nil on O. gossypii. For T. manihoti, r m was 2.3 fold higher on M. tanajoa as prey compared with O. gossypii as prey, while reproduction was nil on T. urticae. An independent experiment on odor-related prey preference of the two predator species (Gnanvossou et al. 2002) showed that T. manihoti and T. aripo preferred odors from M. tanajoa-infested leaves to odors from O. gossypii-infested leaves. Moreover, both predator species preferred odors from M. tanajoa-infested leaves over those from T. urticae-infested leaves. As reported here, life history of the two predatory mites matches odor-related prey preference if the key prey species is compared to the two inferior prey species. The implications of our findings for the persistence of T. manihoti and T. aripo and biological control of M. tanajoa in the cassava agroecosystem in Africa are discussed.
Plant-based foods may serve as alternative resources in meeting the nutritional requirements of p... more 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
New cassava varieties were developed by IITA in order to improve their agronomic yield, pest and ... more New cassava varieties were developed by IITA in order to improve their agronomic yield, pest and disease resistance, and micronutrient content (higher beta-carotene and other carotenoids). This study assessed the ability of 18 new released varieties to produce a traditional cassava food product named “bâton de manioc” in Cameroon central region, in order to maximize their chances of adoption by processors and consumers. Bâton is a steamed cassava mash wrapped in leaves of Megaphrynium macrostachyum, or leaves of other species of Marantaceae. The successive steps of the traditional process were described in details and data on processing yields, material balances, shaping and cooking conditions, as well as production capacity and product quality, were reported. Results showed that “bâton” with both better quality and productivity were obtained from varieties with lower fibre content and larger size of roots. The best profitability was obtained with varieties longer than 25 cm, with a diameter comprised between 6 and 9 cm and a weight comprised between 0.8 and 1.4 kg. Additionally, a survey with processors highlighted the desired quality criteria for cassava varieties to make a good “bâton”. Eight varieties out of the 18 were finally identified as able to be processed into a good “bâton”. Their acceptability by a large number of Cameroonian consumers will be tested in a further study. Beyond these initial results, the originality of the approach was to assess performance and quality criteria for cassava processing in local conditions, which appears very effective to ensure that improved varieties have appropriate characteristics for traditional uses, and also to integrate market and consumers' demands early in varietal improvement programs. (Resume d'auteur)
Two countrywide surveys were conducted in April-May and May-June 2004 throughout the cassava grow... more Two countrywide surveys were conducted in April-May and May-June 2004 throughout the cassava growing belt of Mozambique including several provinces: Gaza, Inhambane, Sofala, Manica, Zambezia, Nampula and Cabo Delgado. Both surveys were planned to assess the distribution, incidence and damage severity of diseases and pests that affect cassava production in Mozambique. Using the methodology developed by the International Institute of Tropical Agriculture (IITA), 202 and 175 cassava fields between 4-8 months old were sampled for pests and diseases in April-May 2003 and May-June 2004, respectively. The results of both surveys showed in the case of diseases that cassava mosaic disease (CMD) was found to be the most widespread disease in Mozambique although the distribution, incidence, and severity varied among provinces, among fields and within fields. The most severe damage was recorded in Gaza, Sofala and Nampula where the average scores were above 3 on a 1-5 damage scale but only in a limited number of sample fields. In other provinces, the disease was either absent or damage symptoms were slight to moderate (2-3). The DNA analysis of the leaf samples coIlected in 2004 throughout the country revealed the presence of several strains of CMD virus including, the African Cassava Mosaic Virus (ACMV), the Eastern African Cassava Mosaic Virus (EACMV), and a combination of both African and EastAfrican Cassava Mosaic Virus (ACMV+EACMV) in 80.5% and 7.6% of the field samples respectiveIy. The devastating East African Cassava Mosaic Virus - Ugandan Strain (EACMVUG2) was absent from all sampled fields. The presence of cassava brown streak disease (CBSD) was confirmed as a serious threat particularly in two of the three Northern provinces of Zambezia and Nampula and at lesser extent in Cabo Delgado. However, the severity was the highest in Zambezia and in the district of Nakala in Nampula province. The other known common tropical diseases of cassava such as the cassava bacterial blight (CBB) and cassava anthracnose disease (CAD) were of minor importance. The cassava green mite (CGM), Mononychellus tanajoa Bondar remained a problem in the southern provinces (Gaza, Inhambane) where the exotic predatory mites Typhlodromalus aripo De Leon was not yet established.. CGM infestations were followed by whitefly (WF) infestations in a rank-order hierarchy of infestation rates. Although generally known as vectors of the cassava mosaic disease (CMD), the high whitefly population densities recorded in some locations (>lo0 adults per plant, e.g. in Zambezia province), was considered a direct pest causing considerable leaf damage and covering plants with sooty molds. The incidence and damage severity of other common pests of cassava (i.e. cassava mealybug, termites, and grasshoppers) appeared insignificant
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Two new mite species of the family Phytoseiidae (Acari: Mesostigmata), Neoseiulus yanineki sp. no... more Two new mite species of the family Phytoseiidae (Acari: Mesostigmata), Neoseiulus yanineki sp. nov. and Typhlodromips cameroonensis sp. nov., are described from Cameroon, Central Africa.
This is the fourth publication of a series to determine the phytoseiid mites of sub-Saharan Afric... more This is the fourth publication of a series to determine the phytoseiid mites of sub-Saharan Africa. Twenty-six phytoseiid species of the subtribes Arrenoseiina Chant & McMurtry (5 species) and Proprioseiopsina Chant & McMurtry (9 species), and tribe Typhlodromipsini Chant & McMurtry (12 species), are reported in this paper. They refer to all species of these taxa known to occur in sub-Saharan Africa. Eight of these species are described for the first time, 14 species are redescribed and 4 are not evaluated in this study. Most of those species were collected in cassava habitat in tropical Africa and in other habitats in South Africa. Keys are included to help in the separation of the species in each tribe or subtribe.
the Centre de Coopération Internationale en Recherche Agronomique pour le Développement (CIRAD), ... more the Centre de Coopération Internationale en Recherche Agronomique pour le Développement (CIRAD), that includes a growing number of research and development partners. RTB brings together research on its mandate crops: bananas and plantains, cassava, potato, sweetpotato, yams, and minor roots and tubers, to improve nutrition and food security and foster greater gender equity especially among some of the world's poorest and most vulnerable populations.
International journal of pest management, Oct 29, 2015
The cotton aphid (Aphis gossypii) is one of the major pests of okra. Eleven okra varieties collec... more The cotton aphid (Aphis gossypii) is one of the major pests of okra. Eleven okra varieties collected from farmers' fields in Cameroon and four aphid-resistant accessions from The World Vegetable Center (AVRDC, Asian Vegetable Research and Development Center) were evaluated from October 2012 to March 2013, and another seven aphid-resistant accessions from AVRDC were evaluated from March to July 2013 at AVRDC's Nkolbisson station, Yaoundé, Cameroon. Accessions selected from these trials were screened in an advanced confirmatory screening in autumn (October–December) 2013 in Shanhua, Taiwan. Results showed that none of the farmers' landraces were resistant to aphids. Two accessions (VI041210 and VI033824) with the lowest aphid populations had the highest trichome density. Analysis of various phytochemicals in selected okra accessions revealed that higher nitrogen and potassium levels made the okra accessions susceptible to aphids during the reproductive stage of the plants. Similarly, the total phenol content was lower in moderately resistant accessions during their reproductive stage. Aphid feeding induced an increase in phenols, and to a lesser extent, tannins. Accessions VI041210 and VI033824 could be incorporated into an integrated pest management strategy to enhance productivity of okra.
Diachasmimorpha longicaudata (Ashmead), a solitary koinobiont larval–prepupal endoparasitoid of f... more Diachasmimorpha longicaudata (Ashmead), a solitary koinobiont larval–prepupal endoparasitoid of fruit flies, was introduced into Kenya for testing and final release against the recently discovered invasive species, Bactrocera invadens Drew, Tsuruta and White in Africa. Laboratory experiments were conducted to determine host preference, host acceptability for oviposition and physiological suitability of B. invadens and five other indigenous tephritid fruit fly species –Ceratitis capitata (Wiedemann), Ceratitis cosyra (Walker), Ceratitis rosa Karsch, Ceratitis fasciventris (Bezzi) and Ceratitis anonae Graham – for the development of D. longicaudata. Females of D. longicaudata visited all host‐larval patches, and were also attracted to these hosts at comparable levels. Acceptability, successful development of parasitoid progenies and their sex ratio varied widely across hosts. C. capitata yielded the highest parasitoid numbers whereas B. invadens was the only host that yielded a female‐biased sex ratio. Larvae of B. invadens, C. rosa, C. fasciventris and C. anonae mounted differential immune reaction towards D. longicaudata eggs. Although, the parasitoid performed poorly on the target host B. invadens, it was able to form new association with C. cosyra and C. capitata. The prospect of using this parasitoid in biological control of African indigenous fruit flies is discussed.
Entomologia Experimentalis Et Applicata, May 22, 2003
Experimental and correlative evidence has steadily mounted over the past 30 years implicating spi... more Experimental and correlative evidence has steadily mounted over the past 30 years implicating spiders in the suppression of insect herbivore pests in crop fields. A large body of evidence has also shown that increasing agroecosystem vegetation diversity often influences the abundance of herbivores and their natural enemies. In previous experiments, the abundance of several species of spiders on grapevines in a raisin grape vineyard was twofold enhanced in vineyard plots vegetationally diversified with a cover crop. A concomitant reduction in the abundance of the leafhopper pest Erythroneura variabilis Beamer was observed on grapevines in the diversified plots, but a causal relationship was not established. In the present study, we simultaneously manipulated spider densities (in open-vine spider exclusion and vine-shoot enclosures) and ground cover to determine their relative impact on E. variabilis population dynamics. Open-vine spider exclusion resulted in an average 35% increase in the density of E. variabilis the greatest effect with occurring during the first and second leafhopper generations. The negative impact of spiders on E. variabilis densities was corroborated with vineshoot enclosure experiments. Under the conditions of the present study, the cover crop per se did not affect the dynamics of E. variabilis populations on grapevines, despite a 1.6-fold increase in spider densities on vines in cover crop plots, compared with vines in bare ground plots, probably due to insufficient spider enhancement and low overall E. variabilis abundance during the summer months. The cover crop had little effect on vine macronutrient status (and presumably vine water status). While this study provided further support for the hypothesis that vegetation diversity can enhance spider abundance, this enhancement does not always lead to lower pest densities, thus underscoring the complexity and variability that exists in interactions involving cover crop, spiders, and crop plants and their herbivore pests.
When predation risk varies in space and time and with predator species, successful prey defence r... more When predation risk varies in space and time and with predator species, successful prey defence requires specific responses to each predator. In cassava fields in Africa, the herbivorous cassava green mite (Mononychellus tanajoa) is attacked by three predatory mite species that are segregated within the plant: the leaf-dwelling Typhlodromalus manihoti and Euseius fustis occur on the middle leaves, whereas the apex-inhabiting T. aripo migrates from the apex to the top leaves only during the night. We found that differential distributions of these predators allow prey to escape predation by vertical migration to other plant strata. We studied the role of odours in the underlying prey behaviour on predator-free plants placed downwind from plants with predators and prey or with prey only. Prey showed increased vertical migration in response to predator-related odours. Moreover, these responses were specific: when exposed to odours associated with T. manihoti, prey migrated upwards, irrespective of the plant stratum where they were placed. Odours associated with T. aripo triggered a flexible response: prey on the top leaves migrated downwards, whereas prey on the middle leaves migrated upwards. Odours associated with E. fustis, a low-risk predator, did not elicit vertical migration. Further experiments revealed that: (1) prey migrate up or down depending on the stratum where they are located, and (2) prey discrimination among predators is based upon the perception of predator species-specific body odours. Thus, at the scale of a single plant, odour-based enemy specification allows herbivorous mites to escape predation by vertical migration.
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