Spatial separation of semiochemical Lurem-TR and entomopathogenic fungi to enhance their compatibility and infectivity in an autoinoculation system for thrips management

BACKGROUNDThe effect of spatial separation of the semiochemical Lurem-TR, which has been found to inhibit conidia of entomopathogenic fungi when put together, on the persistence of conidia of Metarhizium brunneum and M. anisopliae was evaluated in the greenhouse and field in order to develop an autodissemination strategy for the management of Megalurothrips sjostedti on cowpea crop. Influence of spatial separation of the semiochemical on thrips attraction and conidial acquisition by thrips from the autoinoculation device was also investigated in the field.RESULTSPersistence of conidia of M. brunneum and M. anisopliae increased with distance of separation of Lurem-TR. Direct exposure of fungus without separation from Lurem-TR recorded the lowest conidial germination as compared with the other treatments. Attraction of thrips to the device also varied significantly according to distance between device and semiochemical, with a higher number of thrips attracted when Lurem-TR was placed in a container below the device and at 10 cm distance. There was no significant difference in conidial acquisition between spatial separation treatments of conidia and Lurem-TR. Attraction of other insect pests to the device did not significantly vary between treatments. Positive correlations were found between conidial acquisition and thrips attraction.CONCLUSIONThis study suggests that spatial separation of fungal conidia from Lurem-TR in an autoinoculation device could provide a low-cost strategy for effective management of thrips in grain legume cropping systems.</p

Antibiosis and antixenosis of two cowpea varieties to the legume flower thrips

Laboratory investigations were conducted to study the mechanisms of resistance of two cowpea (Vigna unguiculata L. Walp) varieties, ICV 8 and IT84S-2246 to the legume flower thrips, Megalurothrips sjostedti (Trybom) [Thysanoptera: Thripidae]. High mortality of larval stages and slower developmental rates on ICV 8, indicated presence of antibiotic mechanisms of resistance. Adult longevity and oviposition rates of thrips fed on pollen of ICV 8 were greatly reduced. Mean larval and pupal weights were also low on this variety but adult weight was not affected. Mortality rates on IT84S-2246 was low and developmental rates was normal, indicating an absence of antibiotic mechanisms. However, a choice experiment using cowpea flowers, and olfactometer assessment, showed that IT84S-2246 was the least preferred variety, indicating evidence of antixension as the mechanism of resistance in this variety.Des etudes ont ete conduites au laboratoire pour etudier le mecanisme de resistance de deux varietes de niebe (Vigna unguiculata L. Walp), ICV 8 at IT84S-2246, a l'egard du thrips des fleurs de niebe, Megalurothrips sjostedti (Trybom) (Thysanoptera: Thripidae). Une mortalite elevee des stades larvaires ainsi qu'un long developpement larvaire ont ete observes avec la variete ICV 8, montrant ainisi la presence des mecanismes antibiotiques de resistance. La longevite des adultes et le taux d'oviposition des insectes nourris au pollen de la variete ICV 8 etaient considerablement reduits. Les poids moyen des larves et des pupes etait egalement peu eleve avec cette variete; toutefois, le poids des adultes n'etait pas affecte. Avec la variete IT84S-2246, la mortalite etait peu elevee, tandis que le taux de developpement larvaire etait normal, indiquant ainsi l'absence des mecanismes antibiotiques. Cependant, un test a double choix avec les fluers de niebe et un essai dan un olfactometre, ont revele que la variete IT84S-2246 etait la moins preferee, indiquant ainsi que l'antixenose est le mecanisme de resistance pour cette variete

Interactions between Phaedrotoma scabriventris Nixon (Hymenoptera: Braconidae) and Diglyphus isaea Walker (Hymenoptera: Eulophidae), parasitoids of Liriomyza huidobrensis (Blanchard) (Diptera: Agromyzidae)

Liriomyza leafminer flies represent a serious threat to horticultural production in East Africa. Total field parasitism rates recorded in Kenya are below 5%, with the indigenous ectoparasitoid Diglyphus isaea Walker being one of the key parasitoid species. The International Centre of Insect Physiology and Ecology (icipe), in collaboration with the International Potato Centre (CIP), imported into Kenya the endoparasitoid Phaedrotoma scabriventris Nixon to improve natural control of leafminers. The objective of this study was to investigate the interactions between D. isaea and P. scabriventris when used together for the biological control of Liriomyza species. These interactions were studied under laboratory conditions, using treatments that involved single, simultaneous and sequential releases of the different parasitoid species onto plants infested by L. huidobrensis larvae. While used separately, parasitism rates of D. isaea and P. scabriventris were 30.4 ± 10.9% and 63.6 ± 7.7% respectively. However, when used simultaneously, the total parasitism rate increased to 77.0 ± 5.3%. Although P. scabriventris had no effect on D. isaea, the presence of D. isaea reduced the specific parasitism rate of P. scabriventris. In addition, both parasitoids induced leafminer mortality through larval-feeding and stinging. However, feeding and stinging mortality induced by D. isaea (41.9 ± 9.1%) was significantly higher compared to P. scabriventris (11.9 ± 8.7). Similarly, pupal mortality due to feeding and stinging activity was 49.1 ± 6.5% and 21.6 ± 1.9% when exposed to D. isaea and P. scabriventris respectively. The implication for simultaneous use of both parasitoids in East Africa is discusse

Effect of Infection by Metarhizium anisopliae (Hypocreales: Clavicipitaceae) on the feeding and oviposition of the pea leafminer Liriomyza huidobrensis (Diptera: Agromyzidae) on different host plants

The effect of fungal infection by Metarhizium anisopliae on feeding and oviposition of adult Liriomyza huidobrensis was examined on three host plants, faba bean (Vicia faba), French bean (Phaseolus vuklgaris) and snow pea (Pisum sativum) in the laboratory. Flies were contaminated with dry conidia and allowed to feed and oviposit on the different host plants. Mortality in L. huidobrensis varied between 14% and 20% in the controls and between 77% and 100% in fungal treatments 120 h post-infection for the three host plants. L. huidobrensis made more punctures (47.3–52.6 cm-2) in the control than in the fungal treatments (23.1–26.9 cm-2) for the three host plants. The cumulative average number of punctures cm-2/female by L. huidobrensis was higher in the controls than in fungal treatments from 72 h post-treatment in faba bean (12.2 vs. 8.2) and French bean (14.8 vs. 8.9), and from 48 h post-inoculation in snow pea (8.5 vs. 5.7). Female L. huidobrensis laid more eggs in the control (0.6–6.1) than in fungal treatments (0.2–1.5) across the host plants tested. The cumulative mean number of eggs cm-2/female was significantly higher in the controls than in fungal treatments from 48 h post-treatment in faba bean (0.4 vs. 0.2) and French bean (0.1 vs. 0), and 96 h post-inoculation in snow pea (0.2 vs. 0.1). The host plant did not affect the average total number of punctures but had a significant effect on egg laying, with faba bean harboring greater number of eggs in both control and fungal treatments. A proper timeline application of the fungus before onset of feeding and oviposition peaks will be crucial in field suppression of the pest using M. anisopliae. In addition, a great consideration must be given to the target host plants prior to application of the fungus.http://dx.doi.org/10.1016/j.biocontrol.2010.09.01

Endophytic colonization of Vicia faba and Phaseolus vulgaris (Fabaceae) by fungal pathogens and their effects on the lifehistory parameters of Liriomyza huidobrensis (Diptera: Agromyzidae)

Ten fungal isolates belonging to the genera Beauveria (3), Hypocrea (1), Gibberella (1), Metarhizium (2), Trichoderma (1) and Fusarium (2) were evaluated in the laboratory to determine whether they could become endophytic in two pea leafminer (Liriomyza huidobrensis) host plants (Vicia faba and Phaseolus vulgaris), and to assess their possible negative effects on leafminers. Beauveria (ICIPE279), Hypocrea, Gibberella, Fusarium and Trichoderma isolates colonized roots, stems and leaves of both host plant species. Beauveria isolates G1LU3 and S4SU1 colonized roots, stems, and leaves of P. vulgaris but only the root and stem of V. faba. Isolates of Metarhizium failed to colonize the two host plants. The effects of endophytically colonized fungal pathogens on mortality, oviposition, emergence and longevity of L. huidobrensis were investigated after endophytic colonization of V. faba plants. All the fungal isolates that succeeded in colonizing the host plant were pathogenic to L. huidobrensis, causing 100 % mortality within 13.2 ± 0.7–15.0 ± 0.6 d. However, Hypocrea outperformed the other isolates (p < 0.0 001) in reducing longevity of the progeny (11.2 ± 1.0 vs. 17.8 ± 1.4 d in the control), the number of pupae (80.0 ± 6.7 vs. 387.0 ± 21.7 pupae in the control), and adult longevity (3.8 ± 1.0 vs. 9.9 ± 1.8 d in the control). Adult emergence was significantly reduced (p < 0.0 001) in Hypocrea (21.4 %) and Beauveria (38.0 %) treatments compared to the control (82.9 %).http://www.journals.elsevier.com/fungal-ecology

Selection of fungal isolates for virulence against three aphid pest species of crucifers and okra

Published online: 04 June 2016Aphids are regarded as important pest problems of vegetable crops worldwide. Most vegetable growers in sub-Saharan Africa heavily rely on synthetic chemical insecticides for aphids’ control. Fungus-based biopesticides are being considered as alternatives to chemical insecticides. This study evaluates virulence of five isolates of Metarhizium anisopliae and three of Beauveria bassiana against Brevicoryne brassicae, Lipaphis pseudobrassicae, and Aphis gossypii, and their thermotolerance and conidial yield as a prerequisite for strain selection. The study also evaluates performance of the best isolate in screenhouse experiment against target aphid species. Three isolates of M. anisopliae ICIPE30, ICIPE62, and ICIPE69 outperformed the others, causing mortality of 85–98 %, 83–97 %, and 73–77 %, in B. brassicae, L. pseudobrassicae, and A. gossypii, respectively, 7 days post-inoculation. Isolate ICIPE62 had the shortest LT50 values of 3.4, 2.5, and 2.6 days at 1 × 108 conidia ml−1, and the lowest LC50 values of 7.3 × 105, 9.3 × 104, and 3.0 × 104 conidia ml−1 on day 7 against A. gossypii, B. brassicae, and L. pseudobrassicae, respectively. Furthermore, ICIPE62 produced more conidia on the surface of aphid cadavers than ICIPE30 and ICIPE69 and showed wider thermotolerance with optimum ranges between 25 and 30 °C. Application of conidia of ICIPE62 formulated in aqueous and emulsifiable formulations negatively affected aphid population growth rate on kale and okra plants compared to controls in screenhouse experiments. These results have demonstrated the potential of M. anisopliae isolate ICIPE62 in suppression of A. gossypii, B. brassicae, and L. pseudobrassicae populations and could therefore be considered as biopesticide candidate for the control of these target aphids

Interactions among vegetable-infesting aphids, the fungal pathogen Metarhizium anisopliae (Ascomycota: Hypocreales) and the predatory coccinellid Cheilomenes lunata (Coleoptera: Coccinellidae)

Published online: 06 Nov 2015Entomopathogenic fungi are among biocontrol agents being considered for the control of aphids on a variety of crops. Predatory coccinellids, although generalist, are also among important natural enemies that must be conserved for aphid management. Laboratory studies were carried out to investigate the interaction between three vegetable-infesting aphids, Metarhizium anisopliae isolate ICIPE 62 and the coccinellid predator Cheilomenes lunata. At a concentration of 1 × 108 conidial ml–1, the fungus was found to cause mortality of 7.5% to C. lunata, compared to 2.5% mortality in the control at 10 days post-treatment. Female adult C. lunata to which fungus-infected aphids were offered as prey never accepted them as food source in non-choice bioassays. However, live and dead non-infected aphids were fed upon. In choice bioassay, a total of 1–3 out of 24 infected non-sporulating aphids per species (average of 0.1–0.4 aphids per arena) were consumed by 48 h-starved C. lunata within a period of 60 min, but avoided sporulating cadavers. Foraging adult C. lunata enhanced the spread of conidia of M. anisopliae from infected cadavers to fourth instars Aphis gossypii feeding on okra (0.8–15.0% mortality), Brevicoryne brassicae (3.3–15.0% mortality) and Lipaphis pseudobrassicae (0.8–14.2% mortality) on kale plants. Results of this study demonstrate compatibility between M. anisopliae and C. lunata, and could provide a sustainable strategy for effective management of aphids on crucifers and okra cropping systems

Effects of entomopathogenic fungus Metarhizium anisopliae on non-target ants associated with Odontotermes spp. (Isoptera: Termitidae) termite mounds in Kenya

doi:10.1017/S1742758416000114Termites are an important component of savannah ecosystems throughout Africa. Despite their importance in the ecosystem, they can be serious pests of structures, houses, rangelands, tropical forestry, and agriculture. For many decades, chemical insecticides have remained popular for termite management worldwide. However, with the growing environmental concerns over pesticides, biological control using entomopathogenic fungi such as Metarhizium anisopliae (Metschnikoff) Sorokin has become an often-considered alternative. Metarhizium anisopliaeis an ubiquitous, naturally occurring pathogen, which has been reported infecting over 200 insect species; therefore, there is concern that use of M. anisopliae may affect non-target organisms. The effects of M. anisopliae isolate ICIPE 30 were experimentally tested on the ants which associate with Odontotermes spp. termite mounds. Laboratory bioassays were carried out to assess the effects of direct exposure to M. anisopliae on Crematogaster mimosae and Camponotus spp. In addition, ant diversity was monitored over 18 months from termite mounds treated with M. anisopliae in situ near the Mpala Research Centre in Laikipia District of central Kenya. Results obtained revealed no effects of direct exposure to M. anisopliae isolate ICIPE 30 on the mortality of C. mimosae (F1 = 7.29, P = 0.0072) or Camponotus spp. (F1 = 13.01, P = 0.0004) in the laboratory. No significant difference in Shannon indices of ant diversity from treated and untreated mounds (F1 = 0.016, P = 0.8989) was found. It is evident that M. anisopliae has no negative effects on ants that are associated with Odontotermes spp. termite