Cassava whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), in sub-Saharan African farming landscapes: a review of the factors determining abundance

Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is a pest species complex that causes widespread damage to cassava, a staple food crop for millions of smallholder households in Sub-Saharan Africa. Species in the complex cause direct feeding damage to cassava and are the vectors of multiple plant viruses. Whilst significant work has gone into developing virus-resistant cassava cultivars, there has been little research effort aimed at understanding the ecology of these insect vectors. In this review we critically assess the knowledge base relating to factors that may lead to high population densities of Sub-Saharan African (SSA) Bemisia tabaci species in cassava production landscapes of East Africa. We focus first on empirical studies that have examined biotic or abiotic factors that may lead to high populations. We then identify knowledge gaps that need to be filled to deliver long-term sustainable solutions to manage both the vectors and the viruses that they transmit. We found that whilst many hypotheses have been put forward to explain the increases in abundance witnessed since the early 1990s, there are little available published data and these tend to have been collected in a piecemeal manner. The most critical knowledge gaps identified were: (i) understanding how cassava cultivars and alternative host plants impact B. tabaci population dynamics and its natural enemies; (ii) the impact of natural enemies in terms of reducing the frequency of outbreaks and (iii) the use and management of insecticides to delay or avoid the development of resistance. In addition, there are several fundamental methodologies that need to be developed and deployed in East Africa to address some of the more challenging knowledge gaps

Nestmate interactions and egg-laying behaviour in the queenless ponerine ant Rhytidoponera sp. 12

Rhytidoponera sp. 12 is a polygynous Australian arid-zone queenless ponerine ant with morphologically identical mated workers (gamergates) and unmated workers. Discriminating gamergates from virgin workers in R. sp. 12 is therefore difficult. All females have functional ovaries and spermatheca. The ability of unmated workers to lay trophic eggs has not been reported. In four R. sp. 12 colonies we found that gamergates have tough reddish-brown cuticle differing from that of the dark brown unmated workers. Gamergates were successfully identified by combining this observable morphological difference with previously described behavioural traits thus eliminating the need of identification through dissection. In a laboratory-kept colony gamergates showed mutual tolerance. Egg-shuffling behaviour by gamergates was observed. A high proportion of unmated workers laid trophic eggs that were either cannibalised or shared between nestmates; larvae were observed to feed exclusively on these trophic eggs. Eggs laid by gamergates were sometimes eaten, although the majority of these were deposited onto egg piles carried by unmated workers. Oophagy of viable eggs by gamergates may represent a form of dominance behaviour or, together with egg-shuffling, a behaviour to resist manipulation by less fecund gamergates. Removing gamergates from three colonies led to oocyte development in some unmated workers, indicating that ovarian development in virgin workers may be reduced in the presence of gamergates

Microsatellite analysis of gamergate relatedness of the queenless ponerine ant Rhytidoponera sp. 12

Rhytidoponera sp. 12 is a queenless ponerine ant. Reproduction is only by several to many mated workers (gamergates). Until now there has been no information on the variation in relatedness between colonies of such ants. Here we use data from five highly polymorphic microsatellite markers to determine the intracolony relatednesses of cohabiting gamergates (bgg) collected from five colonies. Contrary to expectations from previous work, cohabiting gamergates are highly related, and colonies were provisionally classified into 2 types based on bgg: Type 1 colonies have full sister gamergates, while in Type 2 colonies gamergates are not full sisters, although still significantly related. The high relatedness observed between nestmate gamergates despite the low relatedness expected on theoretical grounds, the observed low relatedness between unmated nestmates, and the genetic signatures of migration between colonies indicates frequent bottlenecking, such as from colony founding events or catastrophic reductions in the numbers of gamergates per colony

Molecular markers to discriminate among four pest species of Helicoverpa (Lepidoptera: Noctuidae)

The four significant pest species in the Helicoverpa genus (H. armigera, H. assulta, H. punctigera and H. zea) are morphologically similar and can only be reliably distinguished through dissection of adult genitalia. Two partial regions of the mitochondrial DNA (mtDNA), the cytochrome oxidase subunit I (COI) and the cytochrome b (Cyt b) genes were amplified by PCR and digested with restriction endonucleases. The restriction patterns, generated by the endonucleases BstZ17I and HphI, demonstrated reliable differentiation of the four Helicoverpa pest species. This technique is fast, reliable and effective at distinguishing specimens irrespective of their life stages and offers support to conventional taxonomic differentiation based on morphological characters

RAT: A quick (and dirty?) push for mobility support

10.1109/MCSA.1999.749275Proceedings - WMCSA'99: 2nd IEEE Workshop on Mobile Computing Systems and Applications32-4

Spodoptera frugiperda: Ecology, Evolution, and Management Options of an Invasive Species

The fall armyworm (FAW), Spodoptera frugiperda (Lepidoptera, Noctuidae), is a well-known agricultural pest in its native range, North and South America, and has become a major invasive pest around the globe in the past decade. In this review, we provide an overview to update what is known about S. frugiperda in its native geographic ranges. This is followed by discussion of studies from the invaded areas to gain insights into S. frugiperda's ecology, specifically its reproductive biology, host plant use, status of insecticide resistance alleles, and biocontrol methods in native and invasive regions. We show that reference to host strains is uninformative in the invasive populations because multidirectional introduction events likely underpinned its recent rapid spread. Given that recent genomic analyses show that FAW is much more diverse than was previously assumed, and natural selection forces likely differ geographically, region-specific approaches will be needed to control this global pest

Optimal design of a tuning fork gyroscope and its testing experiment

2000 International Conference on Modeling and Simulation of Microsystems - MSM 2000621-62

Equilibrium analysis through separation of user and network behavior

10.1016/j.comnet.2008.09.008Computer Networks52183405-3420CNET

The prevalence of and risk factors for pterygium in an urban Malay population: The Singapore Malay Eye Study (SiMES)

10.1136/bjo.2008.150847British Journal of Ophthalmology948977-981BJOP

Elevated blood pressure is associated with rarefaction of the retinal vasculature in children

10.1167/iovs.11-8835Investigative Ophthalmology and Visual Science531470-474IOVS