Risk of spread of the Asian citrus psyllid Diaphorina citri Kuwayama (Hemiptera: Liviidae) in Ghana

The impact of invasive species on biodiversity, food security and economy is increasingly noticeable in various regions of the globe as a consequence of climate change. Yet, there is limited research on how climate change affects the distribution of the invasive Asian citrus psyllid Diaphorina citri Kuwayama (Hemiptera:Liviidae) in Ghana. Using maxnet package to fit the Maxent model in R software, we answered the following questions; (i) what are the main drivers for D. citri distribution, (ii) what are the D. citri-specific habitat requirements and (iii) how well do the risk maps fit with what we know to be correctly based on the available evidence?. We found that temperature seasonality (Bio04), mean temperature of warmest quarter (Bio10), precipitation of driest quarter (Bio17), moderate resolution imaging spectroradiometer land cover and precipitation seasonality (Bio15), were the most important drivers of D. citri distribution. The results follow the known distribution records of the pest with potential expansion of habitat suitability in the future. Because many invasive species, including D. citri, can adapt to the changing climates, our findings can serve as a guide for surveillance, tracking and prevention of D. citri spread in Ghana.

First report on the presence of huanglongbing vectors (Diaphorina citri and Trioza erytreae) in Ghana

As significant threats to global citrus production, Diaphorina citri (Kuwayama; Hemiptera: Psyllidae) and Trioza erytreae (Del Guercio; Hemiptera: Triozidae) have caused considerable losses to citrus trees globally. Diaphorina citri vectors "Candidatus Liberibacter asiaticus" and "Ca. L. americanus", whereas T. erytreae transmits "Ca. L. africanus" and "Ca. L. asiaticus", the pathogens responsible for citrus greening disease or Huanglongbing (HLB). Though HLB is a destructive disease of citrus wherever it occurs, information on the occurrence and geographical distribution of its vectors in Africa is limited. In recent surveys to determine if HLB vectors are present in Ghana, we observed eggs, nymphs, and adults of insects suspected to be D. citri and T. erytreae. Using morphological traits and DNA analyses, the identity of the suspected insects was confirmed to be D. citri and T. erytreae. Individuals of D. citri and T. erytreae were examined using qPCR for CLaf, CLam, and CLas, but none of them tested positive for any of the Liberibacter species. Herein we report, for the first time, the presence of D. citri and T. erytreae in Ghana (West Africa). We discuss the implications of this new threat to the citrus industry to formulate appropriate management strategies.

Modeling climate change impacts on potential global distribution of Tamarixia radiata Waterston (Hymenoptera: Eulophidae)

The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama (Hemiptera: Liviidae), is an efficient vector of "Candidatus Liberibacter" species, the causative agents implicated in citrus greening or huanglongbing (HLB). HLB is the most devastating citrus disease and has killed millions of citrus trees worldwide. Classical biological control using Tamarixia radiata Waterston (Hymenoptera: Eulophidae) against ACP has been successful in some regions. Climatic conditions are critical in determining suitable areas for the geographical distribution of T. radiata. However, paucity of information on climate change impacts on the global spread of T. radiata restricts international efforts to manage ACP with T. radiata. We investigated the potential global distribution of T. radiata using 317 native and non-native occurrence records and 20 environmental data sets (with correlation coefficients (|r| > 0.7)). Using the Maximum Entropy model, these data were analyzed for two shared socioeconomic pathways (SSPs) and two time periods (2030s and 2050s). We showed that habitat suitability for T. radiata occurred in all continents except Antarctica. However, the highly suitable areas for T. radiata were found in parts of the Americas, Asia, Africa and Oceania. The climate suitable areas would increase until the 2050s. The predictions showed that mean temperature of coldest quarter and precipitation of warmest quarter were the most important environmental variables that influenced the distribution of T. radiata. The model reliably predicted habitat suitability for T. radiata, which can be adapted in classical biological control programs to effectively manage ACP in an environmentally friendly manner.

Tamarixia radiata global distribution to current and future climate using the climate change experiment (CLIMEX) model

The phloem-limited bacteria, "Candidatus Liberibacter asiaticus" and "Ca. L. americanus", are the causal pathogens responsible for Huanglongbing (HLB). The Asian citrus psyllid Diaphorina citri Kuwayama (Hemiptera: Liviidae) is the principal vector of these "Ca. Liberibacter" species. Though Tamarixia radiata Waterston (Hymenoptera: Eulophidae) has been useful in biological control programmes against D. citri, information on its global distribution remains vague. Using the Climate Change Experiment (CLIMEX) model, the potential global distribution of T. radiata under the 2050s, 2070s, and 2090s for Special Report on Emissions Scenarios A1B and A2 was defined globally. The results showed that habitat suitability for T. radiata covered Africa, Asia, Europe, Oceania, and the Americas. The model predicted climate suitable areas for T. radiata beyond its presently known native and non-native areas. The new locations predicted to have habitat suitability for T. radiata included parts of Europe and Oceania. Under the different climate change scenarios, the model predicted contraction of high habitat suitability (EI > 30) for T. radiata from the 2050s to the 2090s. Nevertheless, the distribution maps created using the CLIMEX model may be helpful in the search for and release of T. radiata in new regions.

Electronic waste control and management in Ghana: A critical assessment of the law, perceptions and practices

The aim of the study was to assess the impact of Ghana's hazardous and e-waste control and management Act 917 of 2016 on current e-waste management practices and the level of awareness among key stakeholders (general public, repairers, wholesalers/retailers, recyclers and importers of electronic items) in the Greater Accra Region of Ghana. Both quantitative and qualitative data were collected and examined in this study. Results showed a low level (12%) of awareness among stakeholders on the e-waste legislation. Almost 13% of respondents had been educated on e-waste management. Community engagement and the mass media were the main sources of information on e-waste. Significant associations between background information of respondents and awareness level on 'Ghana's Act 917' were observed. Relative to general e-waste issues, only education and stakeholder showed significant associations with e-waste legislation and management. The main e-waste disposal methods adopted by respondents were disposal at dumpsites (22.7%), repair and reuse (21.1%) and reselling (20.1%). Almost 10% of respondents made changes to their e-waste disposal practices over the past 5 years. These changes were mainly due to the economic benefits derived from reselling e-waste (37.6%) and the perceived adverse impacts of e-waste on the environment (23.9%). Overall, there is the need to intensify awareness on 'Ghana's Act 917', especially issues regarding sustainable e-waste management practices.

Assessing levels of selected heavy metals with other pollutants in soil and water resources in Nandom District in the semi-arid northwestern Ghana

This study assessed heavy metal contaminations of soils in cultivated fields (or farms) and water samples from rivers, boreholes, and dug-out wells in Nandom District in semi-arid northwestern Ghana. Other parameters of water from the three sources were also measured and then compared to the permissible limits in the literature. The results showed that soils in farms across the study communities significantly (P ≤ 0.05) had higher levels of chromium (Cr = 0.456 ± 0.132 mgkg^-1), iron (Fe = 214.8 ± 1.52 mgkg^-1), lead (Pb = 0.854 ± 0.03 mgkg^-1), nickel (Ni = 2.813 ± 0.4 mgkg^-1), and arsenic (As = 1.753 ± 0.42 mgkg^-1) when compared to permissible limits set by World Health Organization (WHO) and Food and Agricultural Organization (FAO) for food crops. Water from the study sites significantly (P ≤ 0.0001) had lower levels of heavy metals than the permissible limits set by FAO for irrigation of growing crops. Thus, the water sources appear to be safe for irrigation in the study area. Nonetheless, these sources of water in Nandom District had significantly higher levels of total suspended solids, turbidity, and coliforms that were above the maximum limits indicated in the guidelines of WHO and the Government of Ghana for drinking water. Therefore, treatments of water for drinking are required to minimize any potential threats to public health.

Overview and future research needs for development of effective biocontrol strategies for management of Bactrocera dorsalis Hendel (Diptera: Tephritidae) in sub-Saharan Africa

Infestation of fruits by native and invasive fruit flies causes significant economic losses. In most cases, incidence of 'regulated' dangerous fruit flies in orchards results in restrictions on export of fruits from such places to international markets. Unfortunately, use of insecticides applied on foliage and fruits does not kill the fruit-to-soil stages of fruit flies. However, diverse biological control agents (BCAs) do so. Thus, prevalence of native and invasive fruit flies in orchards will require that a combination of BCAs is included in integrated pest management (IPM) programmes. In the case of Bactrocera dorsalis Hendel and other economically important fruit flies found in sub-Saharan Africa (SSA), use of classical biocontrol approach involves concomitant releases of two exotic parasitoids (Fopius arisanus Sonan and Diachasmimorpha longicaudata Ashmead). These non-native wasps may have complemented the indigenous parasitoids in combination with application of entomopathogenic fungi (EPFs) and conservation of predatory ants (Oecophylla longinoda Latreille, with O. smaragdina) in fruit fly IPM plans. Consequently, some levels of decline in fruit infestation have been observed. Although interspecific interactions between BCAs against several insect pests have produced varying results, including threatening the survival of other BCAs, the prevalence of B. dorsalis in orchards across SSA requires further research to investigate effects of coalescing biocontrol approaches in IPM strategies. Therefore, future research into combining parasitoids, EPFs and entomopathogenic nematodes, in addition to conservation of predatory ants (O. longinoda, O. smaragdina and others) in IPM plans may improve the effectiveness of currently used strategies for the management of fruit-infesting tephritids. © 2021 Society of Chemical Industry.

Responses of Anastrepha suspensa, Diachasmimorpha longicaudata, and Sensitivity of Guava Production to Heterorhabditis bacteriophora in Fruit Fly Integrated Pest Management

Caribbean fruit fly, also known as Caribfly or Anastrepha suspensa , is a major tephritid pest of guavas. A virulent entomopathogenic nematode (EPN) species was investigated to suppress the fruit-to-soil stages of Caribflies, which are also attacked by the koinobiont parasitoid Diachasmimorpha longicaudata in south Florida. The main objective was to develop a feasible and cost-effective EPN-application method for integrated pest management (IPM) of Caribfly to improve guava production. Naturally infested guavas were treated with increasing Heterorhabditis bacteriophora infective juvenile (IJ) concentration or rate (0, 25, 50, …, 1,600 IJs cm -2 ) in field trials to measure the optimum IJ rate and then examine sensitivity of producing guavas to inclusion of Heterorhabditis bacteriophora in Caribfly IPM plans. Relative survival of Caribfly in treatments significantly decreased with increasing IJ rate from 0 to 100 IJs cm -2 . Similarly, probability of observing large numbers of parasitoid wasps ( Diachasmimorpha longicaudata ) in EPN treatments significantly declined with increasing IJ rate (0-100 IJs cm -2 ), even though the non-target effects of Heterorhabditis bacteriophora on relative survival of Diachasmimorpha longicaudata could not be determined because of few emerging parasitoid wasps. Optimum suppression (⩾ 60%) of Caribfly was consistently achieved at 100 IJs cm -2 or 17,500 IJs fruit -1 . Profitability analysis showed that Heterorhabditis bacteriophora can be included in Caribfly IPM tactics to produce guavas. Costs of EPNs in Caribfly IPM are minimized if Heterorhabditis bacteriophora is strategically applied by spot treatment of fruit. Repayment of costs of EPN-augmentation by spot treatments appears achievable by recovering 5.71% of the annual yield losses (⩾1,963 kg ha -1 ≈ US$ 8,650 ha -1 ), which are largely due to Caribfly infestation. Hectare-wide EPN-augmentation (or broadcasting) method requires more fruit recovery than the total annual yield losses to repay its high costs. Profitability of guava production in south Florida will not be very sensitive to marginal costs of the spot treatment method, when compared to the field-wide broadcasting of Heterorhabditis bacteriophora .

Biological control potential of entomopathogenic nematodes for management of Caribbean fruit fly, Anastrepha suspensa Loew (Tephritidae)

BACKGROUND

Caribbean fruit fly (Caribfly) is a serious economic insect pest because of development of larvae that hatch from eggs oviposited into fruits by female adults. This study assessed the virulence of twelve entomopathogenic nematode (EPN) isolates to Caribfly in laboratory bioassays as a starting point toward evaluation of management strategies for the fruit-to-soil-dwelling stages of A. suspensa in fields infested by Caribfly.

RESULTS

Inoculation of A. suspensa with 1 mL of ca 200 IJs larva^-1 killed Caribfly at either larval or pupal stage. Pupae were more resistant to EPN infections than larvae. Adult emergence from inoculated pupae in soil microcosms was significantly lower than that observed in filter paper assays. Longest or largest steinernematids suppressed emergence of more adult Caribfly from pupae in soils, whereas shorter heterorhabditids were more infectious to Caribfly larvae. The highest mortalities of A. suspensa were caused by exotic nematodes Steinernema feltiae and Heterorhabditis bacteriophora, followed by the native Heterorhabditis indica and the exotic Steinernema carpocapsae.

CONCLUSION

Entomopathogenic nematodes reduced the development of Caribfly larvae and pupae to adult in our bioassays, suggesting that EPNs have potential for biological control of A. suspensa. Future work will assess management strategies, using the virulent EPNs, in orchards infested by A. suspensa. © 2016 Society of Chemical Industry.

Damage thresholds and population dynamics of Meloidogyne chitwoodi on carrot (Daucus carota) at different seed densities

Yield loss of carrot (Daucus carota) cv. Nerac caused by Meloidogyne chitwoodi and population dynamics of this nematode were studied using a range of 13 nematode densities at three seed densities (2, 4, 18 seeds pot−1) in a climate-controlled glasshouse. Yield and quality data were fitted to Seinhorst’s yield models. Final population densities were fitted to the population dynamic models for sedentary and free-living nematodes. The tolerance limits for yield loss were 0.34, 0.62 and 0.50, while that of quality were 0.012, 0.142 and 0.813 second-stage juveniles (J2) (g dry soil)−1 at increasing seed densities, respectively. The minimum yield (m), increased with seed density: 0.25, 0.30 and 0.50; the minimum quality yield was 0.10, 0.08 and 0.15 J2 (g dry soil)−1 at increasing seed densities, respectively. Both maximum multiplication rates and maximum population densities increased with increasing seed density but were generally low. Carrot cv. Nerac can be considered a bad host for M. chitwoodi.