Bioecology of some key cashew insect pests and diseases in diverse habitats and landscapes in Tanzania

Cashew (Anacardium occidentale) is an economically important cash crop for many rural households in Tanzania. However, its production is constrained by some insect pests and diseases. As a prerequisite for the development of a more sustainable integrated insect pest and disease management strategy for cashew, information on the biology and ecology of the key insect pests and diseases in a changing environment, and on influencing biotic and abiotic factors, is needed. Surveys were conducted in the major cashew nut‐producing areas of Tanzania for two seasons: August to December, 2009, and August to December, 2010. Data on number of infested and infected shoots by key insect pests and diseases, natural enemies and associated farmer practices, namely synthetic pesticide use and intercropping systems, were collected from different subzones within agroecological zones. Our data showed that abundance and diversity of key cashew insect pests and diseases were influenced by agroecological zones and subzones. Intercropping was more commonly practised in the northern than in the southern zone. Agrochemicals were most frequently used in the southern agroecological zone and affected the occurrence of natural enemies, notably the weaver ant that was more abundant in the northern zone. Furthermore, our findings revealed that Helopeltis sp. and the powdery mildew remained the major constraints to cashew nut production in Tanzania.     

Cross-correlation analysis of invasive mango mealybug and its associated natural enemies in relation to meteorological factors: implications for biological control

Damage caused by invasive downey snow line mealybug, Rastrococcus iceryoides Green (Hemiptera: Pseudococcidae) has been reported to vary between 30% to complete crop loss where no control measure is applied. The current studies seek to determine factors influencing R. iceryoides population outbreaks, parasitoid – host and predator–prey relationships as well as predict optimal management strategies through weather modelling over a period of 28 months from 2008 to 2010 in Tanzania. The highest incidence of R. iceryoides was recorded during the dry season coinciding with the major mango fruiting season. The relationship between R. iceryoides and the parasitoid was positive but not significant, which implies the influence on outbreaks was negligible probably due to low percent parasitism (<12%). However, the predator abundance was directly and significantly related to that of R. iceryoides. Average temperature, average relative humidity, rainfall, and R. iceryoides abundance were autocorrelated to each other. Cross-correlation coef?cients vary significantly from ?0.286 to 0.589 for the pair-variable between R. iceryoides, temperature, relative humidity, rainfall, parasitism and predators. Our findings showed that temperature was the key climatic variable that significantly influenced R. iceryoides outbreaks while rainfall was significantly negatively associated with the pest. Time series analyses show R. iceryoides population increased 4 months after an increase in average temperature in all the sites, 11 months after rainfall and 11 months after relative humidity in Kibaha and Dar es Salaam, respectively. Our findings revealed that R. iceryoides is an excellent target for classical biological control. Thus, the importation of promising co-evolved parasitoid specific to R. iceryoides from the aboriginal home is crucial in formulating an efficient and sustainable management approaches against the invasive mealybug pest in mango agro-ecosystems.     

Distribution,degree of damage and risk of spread of Trioza erytreae (Hemiptera: Triozidae) in Kenya

The African citrus triozid (ACT), Trioza erytreae Del Guercio, is a destructive pest particularly on citrus, and vectors, “Candidatus” Liberibacter africanus (CLaf), which is the causal agent of the African citrus greening disease. Our study seeks to establish the distribution and host‐plant relationship of ACT across citrus production areas in Kenya. We also modelled the risk of spread using the maximum entropy modelling algorithm with known occurrence data. Our results infer that ACT is widely distributed and causes severe damage to four alternative host plants belonging to the family Rutaceae. The adults, immature stages (eggs and nymphs), galls and the percentage of infested leaves were significantly higher in shaded than unshaded trees. However, adult ACTs preferred Kenyan highlands to Victoria Lake and coastal regions. The average area under the curve of the model predictions was 0.97, indicating an optimal model performance. The environmental variables that most influenced the prediction were the precipitation of wettest quarter, precipitation of wettest month, mean diurnal range, temperature seasonality and mean temperature of the coldest quarter. The current prediction of ACT exceeded its existing range, especially in the Western, Nyanza, Central, Rift valley and Eastern regions of Kenya. The model predicted a contraction of suitable habitats for a potential spread in 2040 with an inland shift to higher altitudes in the cooler regions. The potential for further expansion to climatically suitable areas was more pronounced for the 2080 forecast. These findings provide relevant information to improve monitoring/surveillance and designing IPM strategies to limit its spread and damage.     

Taxonomic Identity of the Invasive Fruit Fly Pest,Bactrocera invadens: Concordance in Morphometry and DNA Barcoding

In 2003, a new fruit fly pest species was recorded for the first time in Kenya and has subsequently been found in 28 countries across tropical Africa. The insect was described as Bactrocera invadens, due to its rapid invasion of the African continent. In this study, the morphometry and DNA Barcoding of different populations of B. invadens distributed across the species range of tropical Africa and a sample from the pest''s putative aboriginal home of Sri Lanka was investigated. Morphometry using wing veins and tibia length was used to separate B. invadens populations from other closely related Bactrocera species. The Principal component analysis yielded 15 components which correspond to the 15 morphometric measurements. The first two principal axes contributed to 90.7% of the total variance and showed partial separation of these populations. Canonical discriminant analysis indicated that only the first five canonical variates were statistically significant. The first two canonical variates contributed a total of 80.9% of the total variance clustering B. invadens with other members of the B. dorsalis complex while distinctly separating B. correcta, B. cucurbitae, B. oleae and B. zonata. The largest Mahalanobis squared distance (D² = 122.9) was found to be between B. cucurbitae and B. zonata, while the lowest was observed between B. invadens populations against B. kandiensis (8.1) and against B. dorsalis s.s (11.4). Evolutionary history inferred by the Neighbor-Joining method clustered the Bactrocera species populations into four clusters. First cluster consisted of the B. dorsalis complex (B. invadens, B. kandiensis and B. dorsalis s. s.), branching from the same node while the second group was paraphyletic clades of B. correcta and B. zonata. The last two are monophyletic clades, consisting of B. cucurbitae and B. oleae, respectively. Principal component analysis using the genetic distances confirmed the clustering inferred by the NJ tree.     

Halting ionic shuttle to disrupt the synthetic machinery—Structural and molecular insights into the inhibitory roles of Bedaquiline towards Mycobacterium tuberculosis ATP synthase in the treatment of tuberculosis

Therapeutic targeting of the adenosine triphosphate (ATP) machinery of Mycobacterium tuberculosis (Mtb) has recently presented a potent and alternative measure to halt the pathogenesis of tuberculosis. This has been potentiated by the development of bedaquiline (BDQ), a novel small molecule inhibitor that selectively inhibits mycobacterial F₁F_o-ATP synthase by targeting its rotor c-ring, resulting in the disruption of ATP synthesis and consequential cell death. Although the structural resolution of the mycobacterial C₉ ring in co`mplex with BDQ provided the first-hand detail of BDQ interaction at the c-ring region of the ATP synthase, there still remains a need to obtain essential and dynamic insights into the mechanistic activity of this drug molecule towards crucial survival machinery of Mtb. As such, for the first time, we report an atomistic model to describe the structural dynamics that explicate the experimentally reported antagonistic features of BDQ in halting ion shuttling by the mycobacterial c-ring, using molecular dynamics simulation and the Molecular Mechanics/Poisson-Boltzmann Surface Area methods. Results showed that BDQ exhibited a considerably high ΔG while it specifically maintained high-affinity interactions with Glu65_B and Asp32_B, blocking their crucial roles in proton binding and shuttling, which is required for ATP synthesis. Moreover, the bulky nature of BDQ induced a rigid and compact conformation of the rotor c-ring, which impedes the essential rotatory motion that drives ion exchange and shuttling. In addition, the binding affinity of a BDQ molecule was considerably increased by the complementary binding of another BDQ molecule, which indicates that an increase in BDQ molecule enhances inhibitory potency against Mtb ATP synthase. Taken together, findings provide atomistic perspectives into the inhibitory mechanisms of BDQ coupled with insights that could enhance the structure-based design of novel ATP synthase inhibitors towards the treatment of tuberculosis.     

Host suitability and feeding preference of the African citrus triozid Trioza erytreae Del Guercio (Hemiptera: Triozidae), natural vector of “Candidatus Liberibacter africanus”

African citrus greening (ACGD) and huanglongbing (HLB) diseases are the most damaging diseases of citrus worldwide. Currently, the disease has no cure and has been attributed to the collapse of the citrus industry in several countries. In Africa, the causative agent “Candidatus” Liberibacter africanus is vectored by African citrus triozid (ACT) Trioza erytreae Del Guercio (Hemiptera: Triozidae). African citrus triozid is native to Africa but has been recently reported in Asia and Europe. Apart from citrus, Murraya koenigii (L.) and Clausena anisata (Willd) Hook. F. ex Benth. are also considered as preferred host plants. At present, there is scant information on host plant suitability and preference of T. erytreae. Also, there are contradictory reports on its reproduction and survival on rutaceous and non‐rutaceous host plants. In the present study, we tested the suitability and preference of rutaceous and non‐rutaceous trees and shrubs as potential ACT host plants in choice and no‐choice bioassays. The development from egg to the adult stage was longest on Calodendrum capense (Wright & Arn.) Engl. Host plants of superior quality accordingly to several ACT's biological parameters measured also revealed significantly higher morphometric characteristics. Our findings on the host status of the five rutaceous plants imply that these plants can greatly influence the population dynamics of ACT as well as the epidemiology of ACGD, and these can be a useful guide in the area‐wide management of the pest in Kenya.     

Colon Necrosis Due to Sodium Polystyrene Sulfonate with and without Sorbitol: An Experimental Study in Rats

Introduction

Based on a single rat study by Lillemoe et al, the consensus has been formed to implicate sorbitol rather than sodium polystyrene sulfonate (SPS) as the culprit for colon necrosis in humans treated with SPS and sorbitol. We tested the hypothesis that colon necrosis by sorbitol in the experiment was due to the high osmolality and volume of sorbitol rather than its chemical nature.

Methods

26 rats underwent 5/6 nephrectomy. They were divided into 6 groups and given enema solutions under anesthesia (normal saline, 33% sorbitol, 33% mannitol, SPS in 33% sorbitol, SPS in normal saline, and SPS in distilled water). They were sacrificed after 48 hours of enema administration or earlier if they were very sick. The gross appearance of the colon was visually inspected, and then sliced colon tissues were examined under light microscopy.

Results

1 rat from the sorbitol and 1 from the mannitol group had foci of ischemic colonic changes. The rats receiving SPS enema, in sorbitol, normal saline, distilled water, had crystal deposition with colonic necrosis and mucosal erosion. All the rats not given SPS survived until sacrificed at 48 h whereas 11 of 13 rats that received SPS in sorbitol, normal saline or distilled water died or were clearly dying and sacrificed sooner. There was no difference between sorbitol and mannitol when given without SPS.

Conclusions

In a surgical uremic rat model, SPS enema given alone or with sorbitol or mannitol seemed to cause colon necrosis and high mortality rate, whereas 33% sorbitol without SPS did not.     

Circulating urokinase receptor as a cause of focal segmental glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) is a cause of proteinuric kidney disease, compromising both native and transplanted kidneys. Treatment is limited because of a complex pathogenesis, including unknown serum factors. Here we report that serum soluble urokinase receptor (suPAR) is elevated in two-thirds of subjects with primary FSGS, but not in people with other glomerular diseases. We further find that a higher concentration of suPAR before transplantation underlies an increased risk for recurrence of FSGS after transplantation. Using three mouse models, we explore the effects of suPAR on kidney function and morphology. We show that circulating suPAR activates podocyte β(3) integrin in both native and grafted kidneys, causing foot process effacement, proteinuria and FSGS-like glomerulopathy. Our findings suggest that the renal disease only develops when suPAR sufficiently activates podocyte β(3) integrin. Thus, the disease can be abrogated by lowering serum suPAR concentrations through plasmapheresis, or by interfering with the suPAR-β(3) integrin interaction through antibodies and small molecules targeting either uPAR or β(3) integrin. Our study identifies serum suPAR as a circulating factor that may cause FSGS.     

CXCL10 Gene Promoter Polymorphism -1447A>G Correlates with Plasma CXCL10 Levels and is Associated with Male Susceptibility to Cerebral Malaria

The risk factors for cerebral malaria (CM) and the wide variation in clinical manifestations of malaria are poorly understood. Recent studies indicate that interferon gamma inducible chemokine, CXCL10, is a strong predictor of both human and experimental cerebral malaria. Increased plasma and cerebrospinal fluid levels of CXCL10 were tightly associated with fatal CM in Indian and Ghanaian patients. In the present study, we hypothesized that in a subset of malaria patients, CM susceptibility is associated with variation in CXCL10 expression. We determined whether polymorphisms in the CXCL10 gene promoter region played a role in the clinical status of malaria patients and addressed the genetic basis of CXCL10 expression during malaria infection. Following extensive bioinformatics analyses, two reported single nucleotide polymorphisms in the CXCL10 promoter (−135G>A [rs56061981] and −1447A>G [rs4508917]) were identified among 66 CM and 69 non-CM Indian patients using PCR-restriction fragment length polymorphism assay. Individuals with the −1447(A/G) genotype were susceptible to CM (adjusted odds ratio [AOR] = 2.60, 95% CI = 1.51–5.85, p = 0.021). In addition, individuals with the −1447(A/G) genotype had significantly higher plasma CXCL10 levels than individuals with the −1447(A/A) genotype. Stratifying patients according to gender, the observed association of CM with over expression of CXCL10 were more pronounced in males than in female patients (AOR = 5.47, 95% CI = 1.34–22.29, p = 0.018). Furthermore, −135G>A polymorphism conferred a decreased risk of CM among males (AOR = 0.19, 95% CI = 0.05–0.78, p = 0.021). Polymorphisms in the CXCL10 gene promoter sequence were associated with increased CXCL10 production, which is linked to severity of CM. These results suggest that the −1447A>G polymorphism in CXCL10 gene promoter could be partly responsible for the reported variation underlying severity of CM outcomes particularly in males.