Carmelo Rapisarda

Determination of baseline susceptibility of European populations of Tuta absoluta (Meyrick) to indoxacarb and chlorantraniliprole using a novel dip bioassay method.

BACKGROUND Tuta absoluta(Meyrick) is one of the most serious pests of tomato recently introduced in the Mediterranean region. A novel bioassay method designed for the accurate determination of insecticide toxicity on T. absoluta (IRAC method No. 022) was validated by three different laboratories [Greece (NAGREF), Italy (UC) and Spain (UPCT)] on European populations. RESULTS The insecticides indoxacarb and chlorantraniliprole were used as reference products. The IRAC leaf dip method is easy to perform, producing repeatable, homogeneous responses. LC(50) values for indoxacarb ranged between 1.8 and 17.9 mg L(-1) (NAGREF), 0.93 and 10.8 mg L(-1) (UC) and 0.20 and 0.70 mg L(-1) (UPCT), resulting in a tenfold, 12-fold and fourfold difference between the least and most susceptible populations at each laboratory respectively. For chlorantraniliprole, LC(50) values ranged between 0.10 and 0.56 mg L(-1) (NAGREF), 0.23 and 1.34 mg L(-1) (UC) and 0.04 and 0.24 mg L(-1) (UPCT), resulting in a sixfold difference in all three cases. Overall, UPCT reported lower mean LC(50) to indoxacarb, while UC reported higher LC(50) to chlorantraniliprole. CONCLUSIONS The new bioassay is reliable, providing a useful tool in the design of IRM strategies. Within each country/lab, the variability observed in the results for both indoxacarb and chlorantraniliprole can be attributed to natural variation. Future research is necessary to determine the extent to which it is possible to compare results among laboratories.

Biology and management of Bemisia whitefly vectors of cassava virus pandemics in Africa.

Cassava mosaic disease and cassava brown streak disease are caused by viruses transmitted by Bemisia tabaci and affect approximately half of all cassava plants in Africa, resulting in annual production losses of more than

Potential Toxicity of α-Cypermethrin-Treated Nets on Tuta absoluta (Lepidoptera: Gelechiidae)

US 1 billion. A historical and current bias towards virus rather than vector control means that these diseases continue to spread, and high Bemisia populations threaten future virus spread even if the extant strains and species are controlled. Progress has been made in parts of Africa in replicating some of the successes of integrated Bemisia control programmes in the south-western United States. However, these management efforts, which utilise chemical insecticides that conserve the Bemisia natural enemy fauna, are only suitable for commercial agriculture, which presently excludes most cassava cultivation in Africa. Initiatives to strengthen the control of B. tabaci on cassava in Africa need to be aware of this limitation, and to focus primarily on control methods that are cheap, effective, sustainable and readily disseminated, such as host-plant resistance and biological control. A framework based on the application of force multipliers is proposed as a means of prioritising elements of future Bemisia control strategies for cassava in Africa.

First record of the red gum lerp psyllid, Glycaspis brimblecombei Moore (Hemiptera Psyllidae), in Tunisia

ABSTRACT Insect-proof nets are thought to be effective physical barriers to protect tomato crops against several insect pests, including the invasive tomato pest, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae). However, protected tomato crops are frequently infested by this destructive pest, and there is a higher infestation of plants closer to openings in Mediterranean greenhouses, suggesting that immigrating adults can easily walk on these protective materials and find a way to reach the crop. Laboratory bioassays were carried out to characterize the potential toxicity of &agr;-cypermethrin-treated insect-proof nets (Agronet) against T. absoluta adults. The data showed that the net acts mainly through a variety of chronic sublethal effects rather than acute ones. Reduced longevity and, more markedly, a reduced number of laid eggs were observed after the moths were exposed to the treated net over the duration of their lifetimes. A Y-tube experiment showed that the treated net does not affect the T. absoluta olfaction cues for host location. In contrast, when the moths were given the option to choose either the treated or the untreated net in laboratory cages, they significantly preferred the untreated one. The toxicological significance and the functional implications of these subtle effects for the implementation of integrated T. absoluta management strategies are discussed.

Abundance, diversity and geographic distribution of cassava mosaic disease pandemic-associated Bemisia tabaci in Tanzania

During a survey carried out in August 2013 along all coastal areas of north-eastern Tunisia (governorships of Bizerte, Ariana, Tunis, Ben Arous, Nabeul, Sousse), eucalyptus trees were found to be highly infested by the invasive pest Glycaspis brimblecombei Moore, 1964, also known as red gum lerp psyllid. This insect, native to the Australian region and secondarily dispersed also in the Americas, Mauritius, Madagascar and South Africa, very recently started to invade the Mediterranean region and in almost 5 years has spread to the Iberian Peninsula, Italy, Greece and Morocco. Its presence in Tunisia (which is recorded here for the first time) most probably dates back to summer 2012, since typical necrotic spots caused by the lerp of the psyllid had already been noted on leaves during spring 2013. No presence of its main parasitoid – Psyllaephagus bliteus Riek – nor of any other natural enemy, was noted up to now during our survey in Tunisia.

Mutation in the ace‐1 gene of the tomato leaf miner (Tuta absoluta) associated with organophosphates resistance

Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae), one of the most economically important agricultural pests worldwide, is the vector of cassava mosaic geminiviruses that cause cassava mosaic disease (CMD). In East and Central Africa, a severe CMD pandemic that spread from Uganda in the late 1980s still continues to devastate cassava crops. To assess the association of distinct B. tabaci genetic groups with the CMD pandemic, mitochondrial cytochrome oxidase I gene sequences were analysed from whiteflies collected during surveys conducted from 2010 to 2013 in Tanzania. Four genetic groups – Sub‐Saharan Africa 1 (SSA1), Mediterranean, Indian Ocean and East Africa 1, and a group of unknown whitefly species were identified. SSA1 comprised four subgroups: SSA1‐SG1, SSA1‐SG2, SSA1‐SG1/2 and SSA1‐SG3. SSA1‐SG1 was confined to the pandemic‐affected north‐western parts of Tanzania whilst SSA1‐SG2 and SSA1‐SG3 were found in the central and eastern parts not yet affected by the pandemic. The CMD pandemic front was estimated to lie in Geita Region, north‐western Tanzania, and to be spreading south‐east at a rate of ca 26 km/year. The pandemic‐associated B. tabaci SSA1‐SG1 predominated up to 180 km ahead of the CMD front indicating that changes in whitefly population characteristics precede changes in disease characteristics.

Survey on whiteflies and their parasitoids in cassava mosaic pandemic areas of Tanzania using morphological and molecular techniques

The tomato leaf miner, Tuta absoluta (Lepidoptera: Gelechiidae), is a major invasive pest that has spread throughout many countries in the Mediterranean basin and parts of Asia over the last decade. The control of T. absoluta has relied heavily on the use of chemical insecticides, a strategy that has led to the evolution of resistance. In this study, biological and molecular methods were used to determine the susceptibility of five strains of T. absoluta to the organophosphate chlorpyrifos and to investigate the molecular mechanisms underlying resistance to this class of insecticides. High levels of resistance to chlorpyrifos were observed in all five strains tested. Cloning and sequencing of the gene encoding the organophosphate target site, ace‐1, of T. absoluta revealed the presence of an alanine to serine substitution at a position that has been previously linked with organophosphate resistance across a range of different insect and mite species. The presence of this mutation at high frequency in T. absoluta populations originating from various countries further supports the suggestion that the rapid expansion of this species is, in part, mediated by the resistance of this pest to chemical insecticides.

Identification of mutations associated with pyrethroid resistance in the voltage-gated sodium channel of the tomato leaf miner (Tuta absoluta).

BACKGROUND Bemisia tabaci (Gennadius) is the vector of cassava mosaic geminiviruses (CMGs) and cassava brown streak viruses (CBSVs) in Africa, which cause devastating yield losses. As a prerequisite to developing biological control methods and enhancing knowledge of the fauna of whitefly parasitoids in sub-Saharan Africa, endemic parasitoids were surveyed in the cassava-growing regions of Tanzania and analysed using both morphological and molecular methods. An attempt was made to corroborate the identification of the parasitoid species on the basis of consideration of their morphology and sequence analyses of three DNA fragments, namely partial cytochrome oxidase I (COI), the D2 expansion segment of the 28S rRNA and the internal transcribed spacer I (ITS1). RESULTS Eight whitefly species colonising cassava and twelve species of parasitoids were detected. A species in the Encarsia strenua group and a species in the Eretmocerus mundus group were the most common parasitoids. Molecular systematics indicated the occurrence of two new species of Eretmocerus Haldeman parasitising B. tabaci. CONCLUSION The accurate identification of natural enemies is an essential first step in developing effective biological control solutions for B. tabaci in Tanzania and the wider cassava-growing environments of Africa. The new data provided here represent an important contribution to this goal.