Candidate For Biological Control Research Articles

Genome sequencing and functional analysis of potential Trichoderma species for controlling Pythium schmitthenneri-Induced root rot in olive trees

Root rot disease caused by Pythium schmitthenneri is a significant challenge in olive (Olea europaea L.) cultivation. Due to the limitations of chemical control, this study explores the potential of Trichoderma species as a sustainable alternative with an overview in the genetic properties involved in it. Eight Trichoderma isolates were obtained from olive roots and identified using rDNA internal transcribed spacer (ITS) sequences, revealing four species: T. harzianum, T. longibrachiatum, T. virens, and T. viride. Among these, T. harzianum T-BM6 and T. virens T-KH4, showed 81.4 and 78.77 % inhibition rates of pathogen growth, respectively, in vitro. Greenhouse trials demonstrated that these isolates reduced disease severity to 18.75 % for T-BM6 and 31.25 % for T-KH4. All isolates produced cellulase, with T-BM6 exhibiting high cellulolytic activity. Genomic analysis highlighted key genes related to the MAPK signaling pathway, sulfur metabolism, and inositol phosphate metabolism in T-BM6, and phenylalanine, tyrosine, and tryptophan metabolism in T-KH4. These results suggest that T. harzianum T-BM6 and T. virens T-KH4 are promising candidates for biological control, offering a sustainable alternative to chemical treatments for managing olive root rot.

Improving the Efficiency and Safety of Sentinel Stink Bug Eggs Using X-rays.

Sentinel eggs used to monitor field parasitism of stink bug pests (Hemiptera: Pentatomidae) can only be deployed for a few days to avoid releasing the pest in the monitored area. Using sterile eggs removes the risk of accidental pest introduction and extends deployment time. Freezing the eggs before deployment is one common method of sterilizing sentinel eggs. However, some egg parasitoid species have low or no parasitism on frozen eggs. In this study, X-ray irradiation was used to sterilize Bagrada hilaris sentinel eggs intended for monitoring parasitism by Gryon aetherium (Hymenoptera: Scelionidae), the most promising biological control candidate. In this case, freezing sentinel eggs is not recommended because G. aetherium has low levels of parasitism on frozen eggs. Doses as low as 10 Gy induced 100% sterility. Irradiated eggs successfully sustained the development of G. aetherium and Ooencyrtus californicus (Hymenoptera: Encyrtidae), another egg parasitoid attacking B. hilaris, and parasitism levels were comparable to that of fresh eggs up to seven days old. In addition, G. aetherium showed no preference for fresh non-irradiated eggs over seven-day-old irradiated eggs. Our results indicate that X-ray irradiation is a suitable alternative to produce safe and reliable sentinel eggs to monitor the egg parasitism of B. hilaris and possibly other species.

Black soldier fly (Diptera: Stratiomyidae) larvae reduce cyathostomin (Nematoda: Strongylidae) eggs but develop poorly on horse manure.

Cyathostomins are common digestive tract parasites of grazing horses that spread through contact with horse feces. Horse feces are colonized by a variety of organisms, some of which could serve to reduce parasite loads in horse pastures. Black soldier fly (Hermetia illucens L.; Diptera: Stratiomyidae) larvae (BSFL) could be an ideal candidate for biological control of cyathostomins, due to their near-global distribution, low risk of pathogen transmission, ability to develop on a variety of nutrient-poor substrates (including horse manure), and dramatic effect on microbial communities that cyathostomins depend on. Here, using controlled feeding bioassays, we evaluated the effect of BSFL on cyathostomin egg densities in horse manure while also tracking BSFL performance on manure relative to standard grain-based diets. We found that BSFL consumed less substrate, were slower to reach the prepupal stage, and ultimately yielded less biomass when reared on horse manure compared to grain-based diets. However, BSFL reduced average cyathostomin egg densities in horse manure by over 3-fold. Overall, our results suggest that despite horse manure being a poor substrate for BSFL growth, BSFL effectively reduce cyathostomin egg loads in infected horse manure, though the mechanisms by which they do this are uncertain. While BSFL are known to transform the microbial communities within a diversity of rearing substrates, their effect on larger, parasitic organisms in animal manures may be underappreciated. Promoting the decomposition of infected horse manure with BSFL might be a promising approach to managing parasite populations among grazing horses.

Characterization and screening of new Metarhizium isolates to control the coconut rhinoceros beetle in the Pacific islands

The coconut rhinoceros beetle (CRB; Oryctes rhinoceros) is one of the most destructive insect pests of coconut and oil palms in tropical Asia and the Pacific islands. Members of a new variant, known as CRB-G (clade I), have recently spread into the Pacific islands, causing significant damage. Biopesticides containing Metarhizium spp. are the strongest candidates for inundative biological control against the emerging CRB threat. Selection of the most virulent and robust isolate may determine the impact of this control option on the pest. In this work, CRB specimens with natural fungal infection were collected in Papua New Guinea (PNG) and Solomon Islands (SI). Putative entomopathogenic fungi were isolated and identified. These new isolates and some previously obtained from other Pacific countries were molecularly identified, characterized, and tested for virulence against CRB larval populations in PNG and SI in laboratory bioassays. Of the new isolates collected, four obtained from SI were identified as Metarhizium majus (conidia length ⁓11–15 μm), and four from PNG were identified as Metarhizium pingshaense (conidia length ⁓4–6 μm). The most virulent isolate was M. majus AgR-F717, which caused 100 % mortality in 20–23 days against a CRB variant from the CRB-S grouping (clade II) in laboratory bioassays carried out in PNG. Isolates of M. pingshaense did not show pathogenicity against CRB larvae. M. majus AgR-F717 was also the most virulent in laboratory bioassays using the mixed SI population (from both CRB-S and CRB-G groupings) and was selected for further evaluation using artificial breeding sites. Under field conditions, this isolate demonstrated its ability to infect CRB, dispersal up to 100 m from treated artificial breeding sites, and persistence in soil for at least four months. The new isolate AgR-F717 of M. majus has demonstrated potential as an augmentative biological control agent for CRB in PNG and SI.

Risk assessment of the laboratory host range and a molecular characterisation determining the field host range of Lixus aemulus, for the biological control of Chromolaena odorata in South Africa

Chromolaena odorata (Asteraceae: Eupatorieae) is a sprawling shrub native to the Americas, and a destructive invader of much of the humid tropics and subtropics of the Old World. Opportunistic native-range exploration in 1995 identified a stem-boring weevil, Lixus aemulus, as a promising biological control candidate agent. Host-specificity testing was conducted on L. aemulus in South Africa using laboratory no-choice and paired-choice tests. Three invasive alien plants closely related to C. odorata may be utilized by L. aemulus but no indigenous, ornamental or crop species in South Africa was or is expected to be attacked by the weevil. A native-range field survey was conducted in Brazil to determine the exact identity of the host plant L. aemulus had been collected in 1995, and to identify additional host-plant species. Genetic assessments of the Lixus sp.(p.). adults collected on the three host plants (C. odorata, Chromolaena laevigata and Heterocondylus vitalbae) reveal these individuals are L. aemulus and the weevil can be classed as an oligophage in its native range. Over 5,500 adults were released in South Africa, but overall establishment has been poor. The most likely explanation appears to be a climate mismatch between the region of South Africa invaded by C. odorata and the collection locality in Rio Branco, Acre state, Brazil. Additionally, because the full extent of the native range of L. aemulus is unknown, it is uncertain whether individuals can be sourced from an area whose climate resembles that of South Africa. Furthermore, despite being oligophagous, L. aemulus may perform sub-optimally on the southern African C. odorata biotype.

Effective toxicity of pH to embryonic development of the banded lampeye killifish Aplocheilichthys spilauchen (Duméril, 1861)

The banded lampeye killifish, Aplocheilichthys spilauchen, feeds on larvae of the anopheles mosquito, which makes the fish a good candidate for biological control of malaria. Aquatic organisms require optimal hydrogen ion concentration (pH) for healthy aquatic life, but the impact of pH alteration on A. spilauchen reproductive potential is not known. This study investigated the toxic effect of pH on the embryonic development of A. spilauchen using a static renewal exposure method. Newly fertilised embryos were exposed to a range of pH treatments (5–6 acidic; 7 neutral; 8–9 alkaline) until hatching. All pH media involved triplicates and pH 7 was used as a control. The pH media were checked every 24 h for change and adjusted if necessary. Dissolved oxygen (DO), electrical conductivity (EC), and temperature were monitored throughout the experiment. The endpoints investigated were hatching success, hatchling length, and hatching period. Results indicated a mean hatching success of 95.83 % for pH 7 (neutral) group, while embryos exposed to acidic and basic media recorded lower hatching successes of 60.42 % and 83.34 %, respectively. Hatchling length and hatching period were longer in the control group than in groups of acidic and basic media. Effective toxic pH values of 4.5, 6 and 6.5 were estimated for the hatching period, hatching success, and hatchling length, respectively. These results suggest that sharp changes in the pH of aquatic environments from neutral may adversely impact the reproductive potential of A. spilauchen via embryonic development. This is the first time effective toxic pH values have been estimated for A. spilauchen embryonic development.

Studies on the host selection of a weed biological control candidate facilitate pre-release environmental safety assessments

Pre-release host specificity testing can reliably predict the environmental safety of weed biological control agent (BCA) candidates but typically does not consider their host-finding behavior. Therefore, BCA candidates that do not utilize non-target plants in the field post-release, despite development on such plants in pre-release tests, may be prematurely disqualified for release. We addressed this issue with the seedpod weevil Ceutorhynchus peyerimhoffi, a BCA candidate for the invasive Eurasian mustard Isatis tinctoria. Ceutorhynchus peyerimhoffi weevils, both naive and experienced, were tested for their responses to olfactory, visual, and combined olfactory and visual cues of Braya alpina, Caulanthus heterophyllus, and the US federally listed Boechera hoffmannii. These responses were compared to I. tinctoria or control treatments in a modified Y-tube olfactometer set-up. Naïve and weevils with prior experience on I. tinctoria responded with attraction to olfactory, visual, and combined cues of I. tinctoria. In contrast, there was no attraction by either naïve or experienced weevils to non-target plant cues, except for attraction to C. heterophyllus combined cues by experienced weevils. Furthermore, visual cues of B. alpina and B. hoffmannii were repellent to experienced weevils, and olfactory cues of B. alpina were repellent to naïve weevils. We conclude that C. peyerimhoffi uses visual and olfactory cues to discriminate between its host plant I. tinctoria and North American non-targets. Behavioral host selection studies involving multimodal cues can provide a mechanistic explanation of host selection and complement environmental safety assessments of weed BCA candidates.

Biocontrol efficacy of cajeput oil against Anopheles stephensi L. mosquito and its effect on non-target species.

Chemical insecticides are effective at controlling mosquito populations, but their excessive use can pollute the environment and harm non-target organisms. Mosquitoes can also develop resistance to these chemicals over time, which makes long-term mosquito control efforts challenging. In this study, we assessed the phytochemical, biochemical, and insecticidal properties of the chemical constituents of cajeput oil. Results show that Melaleuca cajuputi essential oil may exhibit mosquito larvicidal properties against Anopheles stephensi larvae (second-fourth instar) at 24h post-treatment. At 24h post-exposure, the essential oil resulted in a significant decrease in detoxifying enzymes. All of these findings indicate that cajeput oil infects An. stephensi larvae directly affect the immune system, leading to decreased immune function. Cajeput oil significantly affects the second, third, and fourth instar larvae of An. stephensi, according to the bioassay results. Cajeput oil does not induce toxicity in non-target Eudrilus eugeniae earthworm species, as indicated by a histological study of earthworms. Phytochemical screening and GC-MS analysis of the essential oil revealed the presence of several major phytochemicals that contribute to mosquito larvicidal activity. The importance of cajeput oil as an effective candidate for biological control of the malarial vector An. stephensi is supported by this study.

Direct Effect of Cannibalism and Intraguild Predation in Menochilus sexmaculatus (Coleoptera: Coccinellidae)

Abstract Menochilus sexmaculatus F. (Coleoptera: Coccinellidae) is a generalist predator with potential as a biological control candidate for suppressing many insect pests, including the cotton mealybug, Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae). However, the potential control capacity of M. sexmaculatus on P. solenopsis may depend not only on its fitness and predatory efficacy, but also on the consequences of both conspecific and heterospecific interactions with other individuals that share the same resource. This study investigated the aggressiveness and vulnerability of different life stages of M. sexmaculatus when encountering various stages of M. sexmaculatus or Harmonia axyridis (Pallas). The results showed that M. sexmaculatus could act as predator and/or prey with the presence of conspecific and heterospecific ladybird beetles. The success of predation is affected by the ladybird beetle life stage and, in most cases, young stages of the ladybird beetles were most susceptible to relatively older life stages of ladybird beetles. Predation between M. sexmaculatus/H. axyridis larvae of the same developmental stage was always asymmetric, favoring H. axyridis. Moreover, M. sexmaculatus exhibited intensive aggressiveness toward their own species over heterospecific individuals, but was more vulnerable to H. axyridis than to M. sexmaculatus individuals. Overall, H. axyridis could negatively affect the population densities of M. sexmaculatus by its high aggressiveness and low vulnerability. However, because our study was conducted in an oversimplified and confined area, more research should be conducted under more realistic conditions to explore the impacts of H. axyridis on the population dynamics of M. sexmaculatus.

Bacillus thuringiensis Bt_UNVM-84, a Novel Strain Showing Insecticidal Activity against Anthonomus grandis Boheman (Coleoptera: Curculionidae).

Bacillus thuringiensis is a Gram-positive bacterium known for its insecticidal proteins effective against various insect pests. However, limited strains and proteins target coleopteran pests like Anthonomous grandis Boheman, causing substantial economic losses in the cotton industry. This study focuses on characterizing a Bacillus sp. strain, isolated from Oncativo (Argentina), which exhibits ovoid to amorphous parasporal crystals and was designated Bt_UNVM-84. Its genome encodes genes for the production of two pairs of binary Vpb1/Vpa2 proteins and three Cry-like proteins showing similarity with different Cry8 proteins. Interestingly, this gene content was found to be conserved in a previously characterized Argentine isolate of B. thuringiensis designated INTA Fr7-4. SDS-PAGE analysis revealed a major band of 130 kDa that is proteolytically processed to an approximately 66-kDa protein fragment by trypsin. Bioassays performed with spore-crystal mixtures demonstrated an interesting insecticidal activity against the cotton boll weevil A. grandis neonate larvae, resulting in 91% mortality. Strain Bt_UNVM-84 is, therefore, an interesting candidate for the efficient biological control of this species, causing significant economic losses in the cotton industry in the Americas.

Biocontrol potential of entomopathogenic nematode, Heterorhabditis indica against pink bollworm, Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae)

BackgroundThe emergence of pink bollworm (PBW), Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae), in cotton due to Bt resistance and concealed feeding habit has created a need for alternative, eco-friendly, and cost-effective control methods. This study aimed to evaluate the bio-efficacy and reproductive potential of two native strains of entomopathogenic nematodes (EPNs), Heterorhabditis indica, namely CICR-HI-CL and CICR-HI-MN, against PBW larvae and pupae under in-vitro conditions.ResultsThe larval assay revealed that strain CICR-HI-CL exhibited higher potency than strain CICR-HI-MN against 2nd, 3rd, and 4th instar larvae, with median lethal dose (LD50) values of 5.45, 4.45, and 4.60 infective juveniles (IJs) per larva, respectively. In case of pupal bioassay, both EPN strains demonstrated greater virulence when applied directly (LD50 values: 29.65 and 73.88 IJs per pupa for strains CICR-HI-CL and CICR-HI-MN, respectively) compared to soil application (147.84 and 272.38 IJs per pupa). Both EPN strains successfully penetrated and reproduced on 4th instar larvae, resulting in maximum production of 19.28 and 20.85 lakh IJs per larva in the next generation when inoculated at 30 IJs per larva.ConclusionThe present study has generated useful information on the virulence and reproductive potential of two strains of EPN H. indica (CICR-HI-CL and CICR-HI-MN) against PBW, a dreaded pest of cotton. Higher virulence and reproductive potential of EPN strains demonstrated their ability to multiply, sustain and perpetuate on larval and pupal stages of PBW. The knowledge generated will help formulate effective management strategies for PBW with the inclusion of EPN as a potential biological control candidate. The soil-dwelling life stages viz., last instar hibernating larvae and pupae of PBW can be the ideal weak links to make a successful use of H. indica for sustainable management of PBW in the cotton ecosystem. However, before taking these EPN strains to field for managing PBW, detailed studies investigating their biocontrol potential against PBW under field conditions are needed.

A biobased superabsorbent formulation for above-ground application of a new entomophthoralean fungus for biological psyllid pest control

Entomophthoralean fungi have long been recognized as promising candidates for biological insect pest control. However, due to technical challenges, no preparation based on these fungi has been established for practical use so far. Low water availability is a key limiting factor of conidial discharge and germination. In the present study, sporulation of psyllid-pathogenic entomophthoralean fungus Pandora cacopsyllae Eilenberg, Keller and Humber (Entomophthorales Entomophthoraceae) was not observable under reduced water activity (aW ≤ 0.97). To support sporulation of encapsulated P. cacopsyllae hyphae from submerged culture under low humidity conditions in above-ground applications in field, we developed a novel paste-type formulation containing biobased superabsorbents, which retained water for a prolonged time period. In co-application with the superabsorbent formulation, the otherwise fast-drying capsules were kept sufficiently moist for sporulation for at least six days in laboratory trials at low humidity below 40%. Using the new formulation, we measured conidial discharge by P. cacopsyllae from the capsules under dry semi-field conditions in summertime by trapping conidia at a vertical distance of up to 40 cm from the sporulation source. By considering the cardinal directions, fewer conidia were discharged on the sun-facing side in the east than on the sun-averted side in the west. The developed formulation improved the sporulation efficacy significantly. Since water availability is a limiting factor for many fungal biocontrol agents, the developed formulation has the potential to also improve their efficacy.

Arthropod associates of Kenyan buffelgrass (Cenchrus ciliaris): a field survey for biological control candidates of a globally important invasive grass

Invasive species are the second largest contributor to biodiversity loss and drivers of ecosystem change. Buffelgrass is a C4, perennial grass native to Africa and Asia that was widely introduced across tropical and subtropical rangelands as livestock forage. Buffelgrass reduces native biodiversity and ecosystem stability in its introduced range when it escapes livestock pastures. Understanding the ecology of insects associated with buffelgrass in its native range may provide an understanding of invasion processes and biological control opportunities where buffelgrass has become an invasive challenge. Here, we present the results of a six-year survey of herbivorous arthropods of a native buffelgrass population from Kenya. Buffelgrass was examined for externally and internally feeding insects of vegetative and reproductive tissues. We also categorised buffelgrass detritivores and parasitoids that may use buffelgrass herbivores as hosts. The samples were photographed and Sanger sequenced to identify them to the lowest possible taxonomic ranking. We collected information on sample abundances, phenologies, tissues consumed, and putative diet breadths. We identified 25 morphospecies representing seven orders and 16 families. The putative host plant specialisation was as high as 67% for Diptera. Phenological variation in herbivore presence correlated with seasonal rainfall and provided a guide for when to conduct follow-up biological control agent searches. The most abundant herbivore was a gall midge (Diptera: Cecidomyiidae) that inhabits buffelgrass culms. Additional research should focus on bringing this species into containment where host choice trials can be conducted to determine if it is truly monophagous and assess its impact on buffelgrass growth.

Isolation and Characterization of Bacteriophage VA5 against Vibrio alginolyticus.

Bacteriophages, or phages, can be used as natural biological control agents to eliminate pathogenic bacteria during aquatic product cultivation. Samples were collected from seafood aquaculture water and aquaculture environmental sewage, and phage VA5 was isolated using the double-layer agar plate method, with Vibrio alginolyticus as the host bacteria. The purified phage strain was subjected to genome sequencing analysis and morphological observation. The optimal multiplicity of infection (MOI), the one-step growth curve, temperature stability, and pH stability were analyzed. Phage VA5 was observed to have a long tail. Whole-genome sequencing revealed that the genome was circular dsDNA, with 35,866 bp length and 46% G+C content. The optimal MOI was 1, the incubation period was 20 min, the outbreak period was 30 min, and the cleavage amount was 92.26 PFU/cell. The phage showed good activity at -20 °C, 70 °C, and pH 2-10. Moreover, the phage VA5 exhibited significant inhibitory effects on V. alginolyticus-infected shrimp culture. The isolated phage VA5 has a wide range of host bacteria and is a good candidate for biological control of pathogenic bacteria.

Evaluating dispersal ability of Venturia canescens Gravenhorst (Hymenoptera: Ichneumonidae) using natural abundance technique and geostatistics

Ectomyelois ceratoniae (Zeller) (Lepidoptera: Pyralidae), is one of the most serious insect pest worldwide. This research was done to evaluate the dispersal ability of Venturia canescens Gravenhorst (Hymenoptera: Ichneumonidae), as one of the larval parasitoids of this pest. The first trial was conducted at three plots consisting of 220 trees in each plot, which separating from each other by at least 100 m, and 13C-enriched V. canescens were released on a single tree at the center of each plot. The traps containing 50 larvae of E. kuehniella was attached at 6, 12, 18, and 24 m intervals in four directions of north, south, west, and east of the release tree. In the second trial, V. canescens were released from a tree where it located in central of each plot (n = 3, each plot = 0.3 ca). geostatistical tools and spatial analysis by distance indices (SADIE) was used to determine distribution of parasitoids in radii of 12, 24, 36 and 48m. Finally, semivariance analysis and isotope ratio indicated that the parasitoids had the highest density in 12 and 24 m radiuses after release while the spatial distribution in higher radii changed toward random or regular patterns. This result revealed that V. canescens could be a potential candidate for biological control of carob moth in pomegranate orchard and it would be attractive to develop the release points to 48 m from each other. Such information would be improved precision or site-specifc applications in agroecosystems and can also be used in site-specific pest management programs.

Insect oviposition in herbaceous plants attracts egg parasitoids despite fungal phytopathogen infection

Egg parasitoids are important natural enemies of several insect pests. The ability to kill the pest before it can inflict damage to the plant makes egg parasitoids ideal candidates for biological control. Several studies have shown that egg parasitoids exploit oviposition-induced plant volatiles (OIPVs) to locate host eggs laid on plant organs. Yet such studies have often overlooked that, in nature, plants frequently suffer concurrent attack by insect herbivores and phytopathogens. These dual attacks can modify the emission of induced plant volatiles, which may potentially interfere with the host location abilities of egg parasitoids. We investigated this research question using the following study organisms: the broad bean Vicia faba, the plant pathogen Stemphylium sp., the southern green stink bug Nezara viridula and its associated egg parasitoid Trissolcus basalis. We showed that T. basalis is able to exploit OPIVs in order to locate N. viridula egg masses even when V. faba plants were previously infected by Stemphylium sp. Chemical analyses indicate that the egg parasitoid ability to exploit OIPVs persists despite significant alterations of the volatile blends emitted by plants suffering multiple biotic stresses. This study highlights the importance of incorporating the complexity of multiple biotic stresses when studying parasitoid foraging behavior, in order to comprehend how to enhance the effectiveness of natural enemies in crop protection.

Prospects of classical biological control of papaya mealybug in Kenya: Performance of its exotic parasitoid, Acerophagus papayae, under laboratory and field conditions

Papaya mealybug (PMB), Paracoccus marginatus, native to Mexico and Central America, invaded Kenya in 2016 causing severe yield losses of between 57% and 91% and £2224/ha household economic losses annually. A classical biological program for PMB involved the importation of Acerophagus papayae, a koinobiont endoparasitoid, from Ghana into the quarantine facility at Kenya Agricultural and Livestock Research Organization, Muguga. Laboratory bioassays were conducted to evaluate the suitability of A. papayae to parasitize PMB. Parasitism rates, sex ratio and development time of the parasitoid were evaluated under choice and no-choice experimental conditions. High parasitism rates of 72.5 ± 5.9 and 75.0 ± 3.8% were recorded in third instar and adult female PMB, respectively, and lower parasitism rates of 43.8 ± 4.6 % were recorded in second instars, under no-choice test conditions. Significant differences in host choice were noted when A. papayae was offered several host stages, with third instars being preferred over second instars. Adult females were preferred over third instars. Adult parasitoids were released and monitored for their establishment at six papaya farms in the Coastal region of Kenya from December 2021 to November 2022. Parasitoid establishment was recovered within the first month of release. Parasitism levels varied across the sites with the highest parasitism of 72.89 % recorded in Kwale. Findings from this study highlight the potential of A. papayae as a good candidate for biological control of PMB in Kenya and Africa beyond.

Native Hymenopteran parasitoids associated with fruit flies (Diptera: Tephritidae) in fruits and vegetables in three ecological zones of Togo

Fruit flies (Diptera: Tephritidae) are major pests associated with fruit and vegetable production in West Africa in general and in Togo in particular. The use of parasitoid wasps to significantly reduce their populations in agroecosystems is a significant component of the integrated management of these pests (IPM-package). To do this, it is important to know their diversity, distribution and potential in controlling fruit flies. In this perspective, the incubation of 28 species of fruits and vegetables sampled in 2009 in ecological zones III, IV and V in Togo allowed to identify five species of native braconid parasitoids: Fopius caudatus Szepligeti, Diachasmimorpha fullawayi Silvestri, Bracon sp., Fopius sp. and Psyttalia sp. F. caudatus was the most abundant making 98.6% of parasitoids recovered. These parasitoids were associated with 4 species of fruit flies, the most abundant being the native species, Ceratitis cosyra (Walker). The parasitism rate in the three ecological zones depended on the locality, the incubated fruit and the fruit fly species. It was relatively low and ranged from 0 to 42.31%, with the highest average rate recorded in the wild fruit, Sarcocephalus latifolius (Sm.) E.A.Bruce, associated exclusively with C. cosyra. Pupae recorded from S. latifolius frequently yielded F. caudatus which was the most abundant. Assessment of the demographic parameters of F. caudatus, a potential candidate for augmentative biological control of C. cosyra in Togo, should be considered under controlled and natural conditions.

Streptomyces silvisoli sp. nov., a polyene producer, and Streptomyces tropicalis sp. nov., two novel actinobacterial species from peat swamp forests in Thailand.

Two novel actinobacterial strains, designated RB6PN23T and K1PA1T, were isolated from peat swamp soil samples in Thailand and characterized using a polyphasic taxonomic approach. The strains were filamentous Gram-stain-positive bacteria containing ll-diaminopimelic acid in their whole-cell hydrolysates. Phylogenetic analysis of their 16S rRNA gene sequences revealed that strain RB6PN23T was most closely related to Streptomyces rubrisoli (99.1 % sequence similarity) and Streptomyces ferralitis (98.5%), while strain K1PA1T showed 98.8 and 98.7% sequence similarities to Streptomyces coacervatus and Streptomyces griseoruber, respectively. However, the average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values were below the species-level thresholds (95-96 % ANI and 70 % dDDH). The genomes of strains RB6PN23T and K1PA1T were estimated to be 7.88 Mbp and 7.39 Mbp in size, respectively, with DNA G+C contents of 70.2 and 73.2 mol%. Moreover, strains RB6PN23T and K1PA1T encode 37 and 24 putative biosynthetic gene clusters, respectively, and in silico analysis revealed that these new species have a high potential to produce unique natural products. Genotypic and phenotypic characteristics confirmed that strains RB6PN23T and K1PA1T represented two novel species in the genus Streptomyces. The names proposed for these strains are Streptomyces silvisoli sp. nov. (type strain RB6PN23T=TBRC 17040T=NBRC 116113T) and Streptomyces tropicalis sp. nov. (type strain K1PA1T=TBRC 17041T=NBRC 116114T). Additionally, a giant linear polyene compound, neotetrafibricin A, exhibiting antifungal activity in strain RB6PN23T, was identified through HPLC and quadrupole time-of-flight MS analysis. The crude extract from the culture broth of strain RB6PN23T exhibited strong antifungal activity against Fusarium verticillioides, Fusarium fujikuroi and Bipolaris zeicola. This finding suggests that strain RB6PN23T could be a promising candidate for biological control of fungal diseases.

Functional and Numerical Responses of Trichogramma euproctidis (Hymenoptera: Trichogrammatidae) to Helicoverpa armigera (Lepidoptera: Noctuidae) Under Laboratory Conditions.

The tomato fruitworm Helicoverpa armigera (Hübner) is regarded as a serious pest that affects a great number of field crops globally. One of the environmentally safe alternatives to the utilization of insecticides is controlling H. armigera via the release of biological control agents by employing parasitoids, e.g., trichogrammatid species. One of the desired parasitoids indigenous to southwestern Iran is Trichogramma euproctidis (Girault). To anticipate the outcomes of augmentative releases of T. euproctidis in the field, the numerical and functional responses of female T. euproctidis that parasitizes the eggs of H. armigera were determined in the laboratory. The densities of host eggs per glass tube arena (length: 10cm, diameter: 1cm) were 2, 4, 8, 16, 32, 64, or 128 individuals. The functional response to the eggs of H. armigera indicated Holling's type II response. The estimated handling time and attack rate from the random parasitoid equation were 0.6898h and 0.00823h, respectively. This indicates that, at the maximum level, each T. euproctidis was capable of parasitizing 34.79 eggs a day. At the 128 host egg density, the number of eggs laid, that is, the numerical response, ascended as the density of host eggs increased up to a maximum of 89.90 eggs per female. According to the obtained results of the present investigation, T. euproctidis can serve as an appropriate candidate for augmentative biological control of H. armigera. Nevertheless, it is necessary to conduct complementary experiments in greenhouses and open fields.