Distribution, abundance and natural enemies of the invasive tomato leafminer, Tuta absoluta (Meyrick) in Kenya

Tuta absoluta (Meyrick) has become a serious menace to sustainable production of tomato in Kenya. A survey was conducted between April 2015 and June 2016 to determine its distribution, abundance, infestation, and damage levels on tomato, and associated natural enemies. Trap counts of T. absoluta moths were recorded in all surveyed 29 counties, which indicated its nationwide distribution irrespective of altitude. Tuta absoluta was present in both open fields and greenhouses. The highest moth/trap/day was 115.38 ± 15.90. Highest leaf infestation was 92.22% and the highest number of mines and larvae per leaf were 3.71 ± 0.28 and 2.16 ± 0.45, respectively. Trap captures in terms of moth/trap/day were linearly and positively related to leaf infestations in open fields (R2 = 0.81) and greenhouses (R2 = 0.61). Highest fruits’ infestation and damage were 60.00 and 59.61%, respectively, while the highest number of mines per fruit was 7.50 ± 0.50. Nesidiocoris tenuis (Reuter) and Macrolophus pygmaeus (Rambur) were identified as predators of T. absoluta larvae. Nine species of larval parasitoids were recovered from infested foliage, with a combined parasitism of 7.26 ± 0.65%. Hockeria species was the most dominant (31.25%) and accounted for 12.88 ± 1.47% parasitism. Two species of larval parasitoids, Hockeria and Necremnus were obtained from sentinel plants with an average parasitism of 1.13 ± 0.25. The overall abundance and parasitism rates of recovered natural enemies were low to effectively control the field populations of T. absoluta. These findings form the basis of researching and developing effective and sustainable management strategies for the pest.

Sensing the future of bio-informational engineering

The practices of synthetic biology are being integrated into ‘multiscale’ designs enabling two-way communication across organic and inorganic information substrates in biological, digital and cyber-physical system integrations. Novel applications of ‘bio-informational’ engineering will arise in environmental monitoring, precision agriculture, precision medicine and next-generation biomanufacturing. Potential developments include sentinel plants for environmental monitoring and autonomous bioreactors that respond to biosensor signaling. As bio-informational understanding progresses, both natural and engineered biological systems will need to be reimagined as cyber-physical architectures. We propose that a multiple length scale taxonomy will assist in rationalizing and enabling this transformative development in engineering biology.

Drift Distance in Aircraft Glyphosate Application Using Rice Plants as Indicators

ABSTRACT: This study aimed to evaluate the potential for glyphosate drift during aerial application using rice plants as sentinels, aiming to determine the effect of drift on irrigated rice crops. For this purpose, a field experiment was performed using an entirely randomized design with four replicates, evaluating different distances from the site of application [control (no application), 0, 12.5, 25, 50, 75, 100, 150, 200, 300, and 400 m]. The experiment was carried out at the Granjas 4 Irmãos farm, located in the Rio Grande city, Rio Grande do Sul State, Brazil. The glyphosate dose application was 1,920 g e.a. ha-1 (Roundup Transorb®, 480 g e.a. L-1 glyphosate isopropylamine salt). A dose-response curve was developed to estimate the drift rate in sentinel plants, by applying increasing glyphosate doses in rice plants and assessing the injury level. The drift rates estimated by the injury level in sentinel plants were 14% (150 m), 13% (200 m), and 5% (400 m). Death of the experimental units was observed for distances between 0 and 50 m, while in distances between 75 and 150 m, 25 to 50% of the plants survived, reducing productivity. In the distances between 200 and 400 m, there was no reduction in productivity when compared to the control, even when the injury levels reached 52 to 82%. Thus, we concluded that a 5% glyphosate drift reached up to 400 m from the application range. Considering the recommendation of zero drift, distances greater than 400 m should be adopted to avoid symptoms in rice plants. We suggest using distances of more than 400 m in future studies.

Field Margin Vegetation in Tropical African Bean Systems Harbours Diverse Natural Enemies for Biological Pest Control in Adjacent Crops

Non-crop vegetation around farmland can be valuable habitats for enhancing ecosystem services but little is known of the importance of field margins in supporting natural enemies of insect pests in tropical agriculture. This study was conducted in smallholder bean fields in three elevation zones to assess the importance of field margin vegetation to natural enemy populations and movement to the bean crop for biological pest control. The pests and natural enemies were assessed using different coloured water pan traps (to ensure the capture of insects with different colour preferences) and the interactions of the two arthropod groups with the margin vegetation and their movement to the bean crop were monitored using fluorescent dye. Sentinel plants were used to assess predation and parasitism levels. A total of 5003 natural enemies were captured, more in the field margin than within the bean field for low and mid elevation zones, while in the high elevation zone, they were more abundant within the bean field. Pests were more abundant in the crop than margins for all the elevation zones. The use of a dye applied to margin vegetation demonstrated that common natural enemy taxa moved to the crop during the days after dye application. The proportion of dye-marked natural enemies (showing their origin to be margin vegetation) sampled from the crop suggest high levels of spatial flux in the arthropod assemblage. Aphid mortality rates (measured by prey removal and parasitism levels on sentinel plants) did not differ between the field edges and field centre in any of the three elevation zones, suggesting that for this pest taxon, the centre of the fields still receive comparable pest control service as in the field edges. This study found that field margins around smallholder bean fields are useful habitats to large numbers of natural enemy taxa that move to adjacent crops providing biological pest control service.

The value of sentinel plants for risk assessment and surveillance to support biosecurity

Effective surveillance for early detection of invasive alien species in natural ecosystems, or on valued plants found in modified areas, could prevent potentially devastating and costly impacts (whether environmental, economic or cultural) of new invasions on the invaded country. Surveillance technologies are often constrained by a range of factors. Determining which species present a significant risk before they reach the border is an effective strategy to minimize the possibility of invasion and/or the impact of invasion. Surveillance of sentinel plants provides an important tool to strengthen biosecurity programs assisting with i) detecting and identifying insect pests, nematodes and plant diseases that could potentially invade uncolonized countries, and ii) developing pest risk analysis profiles to eliminate or mitigate the risk of arrival. This review examines some of the challenges and opportunities provided by sentinel plant research and discusses the factors that could affect the success of their use for biosecurity risk assessment and surveillance in the New Zealand context.

A host immune hormone modifies parasite species interactions and epidemics: insights from a field manipulation

Parasite epidemics can depend on priority effects, and parasite priority effects can result from the host immune response to prior infection. Yet we lack experimental evidence that such immune-mediated priority effects influence epidemics. To address this research gap, we manipulated key host immune hormones, then measured the consequences for within-host parasite interactions, and ultimately parasite epidemics in the field. Specifically, we applied plant immune-signalling hormones to sentinel plants, embedded into a wild host population, and tracked foliar infections caused by two common fungal parasites. Within-host individuals, priority effects were altered by the immune-signalling hormone, salicylic acid (SA). Scaling up from within-host interactions, hosts treated with SA experienced a lower prevalence of a less aggressive parasite, increased burden of infection by a more aggressive parasite, and experienced fewer co-infections. Together, these results indicate that by altering within-host priority effects, host immune hormones can drive parasite epidemics. This study therefore experimentally links host immune hormones to within-host priority effects and parasite epidemics, advancing a more mechanistic understanding of how interactions among parasites alter their epidemics.

Incidence of Viruses in Two Large-Scale Plantings of Blackberry in South Carolina as Detected Through the Use of Sentinel Plants and RT-PCR

Some plants in two large-scale blackberry plantings established from virus-indexed planting material displayed symptoms typical of virus infection in the early days of the growing season immediately after planting. Groups of sentinel plants exposed within the plantings for 30-day periods over additional growing seasons, and subsequently screened for the presence of five viruses by reverse transcription PCR, detected Blackberry yellow vein-associated virus (BYVaV), Blackberry virus Y (BVY), Blackberry chlorotic ringspot virus (BCRV), Blackberry virus E (BVE), and Blackberry leaf mottle-associated virus (BLMaV). Because these viruses are thought to be transmitted through the actions of arthropods, and bearing in mind that the plantings had been established with virus-indexed material, it seems that the viruses must be moving into the new crops from adjacent native vegetation and once established moving freely within the crops. BYVaV has been reported from South Carolina previously. A recent publication reports the detection of BLMaV in samples originating from South Carolina and demonstrates transmission of the virus by mites. This is the first report of the detection of BCRV, BVY, and BVE within the state and provides support for the movement of the latter two viruses (BVY and BVE) within established plantings of blackberry as a result of vector activity.