Infochemical use by predatory mites of the cassava green mite in a multitrophic context

This thesis describes research on multitrophic interactions in a system consisting of (1) cassava plants ( Manihot esculenta ), (2) three herbivorous mites, i.e. the cassava green mite Mononychellus tanajoa, the red spider mite Oligonychus gossypii and the two-spotted spider mite Tetranychus urticae and (3) two exotic predatory mites Typhlodromalus manihoti and T. aripo , in Africa. The objectives are to understand how the two exotic predators (i) exploit chemical information to locate the target prey in pure and mixed odors conditions with the alternative prey mites, (ii) perform when feeding on different prey mite species and (iii) interact with each other.The predatory mites, T. manihoti and T. aripo were attracted to cassava leaves infested by M. tanajoa compared with non-infested leaves, when the predators were starved for 2, 6 or 10 hours. They were not attracted to 400 female M. tanajoa removed from infested plants nor to mechanically wounded leaves. In a choice situation, T. manihoti and T. aripo preferred odors from leaves infested by M. tanajoa to odors from leaves infested by O. gossypii regardless of the ratio M. tanajoa : O. gossypii . When M. tanajoa -infested leaves and T. urticae -infested leaves were offered in a choice situation, the response of the two predator species depended on the density of T. urticae . Typhlodromalus manihoti and T. aripo were attracted to odors from cassava leaves infested with both M. tanajoa and O. gossypii or to a mixture of odors from leaves infested with M. tanajoa and odors from leaves infested with O. gossypii, when compared to odors from non-infested leaves. In contrast, mixed odors from M. tanajoa -infested leaves and T. urticae -infested leaves did not yield a preference over odors from non-infested leaves.Typhlodromalus manihoti and T. aripo had a higher intrinsic rate of population increase (rm) and net reproduction (Ro), and a shorter generation time and doubling time on when they were feeding on M. tanajoa than on O. gossypii or T. urticae . Prey-related odor preference matched predator performance if the key prey is compared to the two inferior prey mite species.Typhlodromalus aripo displayed a marked preference for odors emitted from either infested cassava apices or infested young cassava leaves over infested old cassava leaves but showed equal preference for odors from apices and young leaves both infested with M. tanajoa . Typhlodromalus manihoti did not discriminate between volatiles from the three infested cassava plant parts. This mirrors the differential distribution of the two predators on cassava plant foliage.Carnivorous arthropods when searching for adequate food and habitat for themselves and their progeny should in the meantime avoid becoming food for other organisms. Intraguild interactions have been investigated for the predatory mite species T. manihoti , T. aripo and the native species Euseius fustis . Typhlodromalus manihoti is able to discriminate between odors from patches with con- and heterospecific competitors and prefers to visit patches with heterospecifics. Typhlodromalus aripo preferred to move away from patches with heterospecifics or conspecifics. Euseius fustis avoided odors from patches with conspecifics as well as odors from patches with the heterospecifics T. manihoti and T. aripo .In conclusion, this thesis shows that the distribution and diversity of prey species, intraguild predation and competition are likely to play an important role in infochemical use by T. manihoti and T. aripo . In addition to predator-prey interactions, interactions between predators can also be considered as important factors affecting population dynamics of both prey and predators.</p

Bactrocera Cucurbitae response to four Cymbopogon species essential oils

GC/MS analysis of essential oils extracted from four Cymbopogon species revealed that the majors compounds were trans-p-mentha-1(7),8-dien-2-ol (21.9%), cis-p-mentha-1(7),8-den- 2-ol (19.4%), trans-p-mentha-2,8-dien-1-ol (9.6%), cis-p-mentha-2,8-dien-1-ol (7.2%), cis-pmenth-2-en-1-ol (7.2%), limonene (6.3%) in C. giganteus; piperitone (68.4%); ?-2-carene (11.5%) and ?-eudesmol (4.9%) in C. schoenanthus, while citronellal (41.6%); geraniol (28.2%); citronellol (12.6%) and geranial (41.3%); neral (33.0%); myrcene (10.4%), geraniol (6.5%) were recorded in C. nardus and C. citratus, respectively.Tephritid fruit flies use both olfactory and visual cues to seek food and ovipositional resources. Olfactive effects for C. citratus, C. nardus, C. giganteus and C. schoenanthus essential oils on melon fly (B. cucurbitae) were evaluated using a four-arm olfactometer. The results showed that C. giganteus and C. schoenanthus repel mostly the fruit fly B. cucurbitae, compared with C. nardus and C. citratus and that female and male B. cucurbitae responded similarly to odours emitted from all essential oils evaluated. The number of pupae collected from zucchini treated with C. giganteus was significantly lower than that collected from zucchini treated with C. nardus when exposed to female B. cucurbitae, regardless of the concentrations

Assessment of a liquid larval diet for rearing Dacus species and Bactrocera dorsalis (Diptera: Tephritidae)

Species of the genus Dacus are important insect pests of fruits and vegetables. Two Dacus species, Dacus punctatifrons Karsch and Dacus vertebratus Bezzi, as well as Bactrocera dorsalis (Hendel), were reared on a liquid artificial diet, a carrot (Daucus carota L.)-based solid artificial diet, and a natural fruit host to assess the suitability of the liquid diet for small-scale rearing of these species. Egg hatch, pupal production, adult emergence and F1 productivity were recorded to evaluate performance of the three species on each diet. Egg hatch on the three diets was more than 50% for D.&nbsp;punctatifrons and B.&nbsp;dorsalis, but for D.&nbsp;vertebratus, egg hatch was less than 40% when they were introduced to the liquid artificial diet. Pupal production for both Dacus species was very low or nil on the liquid artificial diet and the carrot-based artificial diet, respectively. Adult emergence was low for D.&nbsp;punctatifrons and nil for D.&nbsp;vertebratus on the liquid artificial diet. This study showed that the two Dacus species did not develop well on either the liquid or solid carrot-based artificial diet whereas B.&nbsp;dorsalis performed well on the liquid diet. Cucumber, the natural host of both Dacus species, was better for small-scale rearing of these species than the liquid and carrot-based artificial diets. Nutrients found in cucumber need to be identified to formulate alternative rearing media for Dacus species that are economical and easy to use

Comparative Effects of Some Botanical Extracts and Chemicals in Controlling the Red Spider Mite Tetranychus evansi Baker & Pritchard on Solanaceous Crops

The tomato red spider mite, Tetranychus evansi, is an invasive pest reported on solanaceous crops in Benin around 2008, causing heavy economic damage. The control of this mite by farmers is mainly done through intensive applications of chemical pesticides that are not always effective. In the present study, we evaluated in a laboratory, at IITA-Benin, the effects of two botanical insecticides: the Cashew Nut Shell Liquid (CNSL) and Neem oil. This is together with Acarius 18 EC, a chemical acaricide generally used by growers on eggs and adult females T. evansi. The half recommended dose (0.5 l/ha), the recommended dose (1 l/ha), and the double recommended dose (2 l/ha) of Acarius and Neem oil as well as solutions at 1%, 2 %, 3%, 4% and 5% of CNSL were tested. Mean egg hatching rates varied significantly among treatments, ranging from 0.00 ± 0.00% (Neem oil and CNSL) (respectively at half recommended dose and 4%) to 100% (Control). Mortality of adult female T. evansi also differed significantly among treatments (P &lt; 0.0001), ranging from 22.00 ± 4.20% to 100%. The highest mortality rates were recorded with Neem oil at any doses and with CNSL at 4%, whereas the lowest rate was recorded with the control treatment. Fecundity of pesticide-treated females T. evansi and proportion of eggs that hatched revealed significant differences among all doses of products (P &lt; 0.0001). It appears from this study that even the half recommended dose of Neem oil and the CNSL at 4% were very effective on suppressing T. evansi populations and should, therefore, be subject to further studies to test their compatibility with natural enemies, and to determine strategies for their efficient applications in greenhouse and under field conditions. &nbsp; &nbsp

Occurrence of Banana bunchy top virus in banana and plantain (Musa sp.) in Benin

In July 2011, banana and plantain that displayed stunting and leaf symptoms typical of banana bunchy top disease were observed to be widespread in Dangbo Commune, Ouémé Department, Benin. To identify the cause of the disease, a roving survey was conducted in December 2011 in nine locations in Avrankou, Dangbo, Akpro-Missérété and Porto-Novo Communes, in Ouémé. In each location, the incidence of symptom-bearing plants was estimated from counts of 15 mats, and samples were collected for Banana bunchy top virus (BBTV) assessment. Approximately 60% of the 94 banana mats assessed had plants exhibiting typical symptoms of BBTV infection - chlorotic leaf margins, dark green streaks on petioles, narrow leaves that bunched at the top, and severe stunting. Total DNA was extracted from 25 leaf samples collected from plants with symptoms; they were then tested for BBTV by polymerase chain reaction. The sequences showed 100% nucleotide sequence identity with a BBTV isolate from Cameroon (FJ580970) and 99-100% identity with several other BBTV isolates from the GenBank database belonging to the South Pacific group, which consisted of BBTV isolates from Africa, Australia, India and South Pacific. This finding confirmed that the virus isolate associated with the diseased plants in Benin was of the BBTV South Pacific type. This is thought to be the first report of BBTV in Benin. The disease is widespread in all the four communes surveyed

Temperature-dependent phenology of the parasitoid Fopius arisanus on the host Bactrocera dorsalis

Fopius arisanus (Sonan), an egg-pupal parasitoid of numerous fruit fly species, was recently introduced into Africa for the control of the Oriental fruit fly, Bactrocera dorsalis (Hendel). In this study, life-table data of F. arisanus were generated under laboratory conditions at six constant temperatures (15, 20, 25, 30, 28 and 35&nbsp;°C; 75% RH, L12:D12 photoperiod) and under variable conditions in a screenhouse on B. dorsalis. Several non-linear functions were fitted to model species development, mortality, longevity and oviposition using the Insect Life Cycle Modeling (ILCYM) software. The established phenology models were stochastically simulated at variable temperatures to estimate the life table parameters. Fopius arisanus completed development from egg to adult at all the temperatures tested except at 35&nbsp;°C. Mean developmental time from egg to adult was inversely proportional to the temperature. The minimum temperature threshold (Tmin) from egg to adult was 8.15&nbsp;°C, while the maximum temperature threshold (Tmax) was estimated at 34.2&nbsp;°C. The optimal temperature for immature stages survival was predicted for 20-30&nbsp;°C. The optimum fecundity estimated was 251 eggs/female at 22&nbsp;°C. Following the stochastic simulations under natural conditions of the selected agro-ecological zones, it appears that the Humid Forest with Bimodal Rainfall provides a suitable thermal condition for potential population growth of F. arisanus. The present study shows the importance of temperature on the demographic parameters of F. arisanus. Implications of present findings on the biological control of B. dorsalis under climate change scenarios is discussed

Tephritid fruit fly species composition, seasonality, and fruit infestations in two central African agro-ecological zones

Open Access Journal; Published online: 13 Nov 2022Bactrocera dorsalis and several Africa-native Ceratitis species are serious constraints to fruit production in sub-Saharan Africa. A long-term trapping and fruit collection study was conducted (2011–2016) in two contrasting agro-ecological zones (AEZs) of Cameroon to determine fruit fly species composition, seasonality, attraction to various lures and baits, and fruit infestation levels. Ten tephritid species from genera Bactrocera, Ceratitis, Dacus, and Perilampsis were captured in traps. Bactrocera dorsalis was the most dominant of the trapped species and persisted throughout the year, with peak populations in May–June. Ceratitis spp. were less abundant than B. dorsalis, with Ceratitis anonae dominating in the western highland zone and Ceratitis cosyra in the humid forest zone. Methyl eugenol and terpinyl acetate captured more B. dorsalis and Ceratitis spp., respectively than Torula yeast. The latter was the most effective food bait on all tephritid species compared with Bio- Lure and Mazoferm. Bactrocera dorsalis was the dominant species emerging from incubated fruits, particularly mango, guava, and wild mango. Four plant species—I. wombolu, Dacryodes edulis, Voacanga Africana and Trichoscypha abut—were new host records for B. dorsalis. This study is the first long-duration and comprehensive assessment of frugivorous tephritid species composition, fruit infestations, and seasonality in Central Africa