Environmental and physiological factors influencing phototactic flight of Bemisia tabaci

Abstract. Experiments were conducted in a glasshouse and in the laboratory to determine the environmental and physiological parameters that affect flight behaviour of Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae). The number of whiteflies taking off and exhibiting a positive response to sky light in the glasshouse was greatest from 08.30 to 10.00 hours. During peak flight activity less than 5% of the population engaged in phototactic orientation. Temperature was the best single predictor for the phototactic response, accounting for 75% of the variability in whitefly ascent. Sex ratios were determined for individuals remaining on poinsettia, Euphorbia pulcherrima (Willd.), and for individuals that exhibited phototactic orientation; both groups deviated from an expected 1:1 ratio. Males were more prevalent on the plants (1:0.76), whereas females were much more prevalent (1:3.02) among the whiteflies responding to sky light. A higher percentage of the females displaying a phototactic response contained eggs when compared to females remaining on poinsettia (87 v 65%). The two groups of females did not differ significantly in their weights, but males that remained on the plants were heavier than males that responded to sky light. Mark–recapture studies and experiments where phototactic individuals were removed from the population established that the response was short-lived. Whiteflies exhibiting a phototactic response in the glasshouse were more likely to exhibit long-duration, phototactic flights in a vertical flight chamber when compared to individuals that remained on poinsettia (80.7 ± 6.7 v 36.0 ± 5.8% phototactic response; 7.0 ±3.2 v 0.7±0.2min flights). There was also less deviation in flight across the horizontal plane among the individuals that exhibited a positive response to sky light in the glasshouse in comparison to individuals that remained on their host. However, initial rates of climb were not significantly different between the two groups of whiteflies.     

Colored shading nets impede insect invasion and decrease the incidences of insect‐transmitted viral diseases in vegetable crops

Black shading nets are commonly used to protect agricultural crops from excessive solar radiation and wind, and for water saving. Recent studies have demonstrated that when black nets were replaced by either red, yellow, or pearl nets (ChromatiNets^?) of equivalent shading capacity, it increased the fruit yield and improved the quality of bell peppers (Capsicum annuum L.) and tomatoes (Solanum lycopersicum L.) (both Solanaceae). We studied the effects of these colored shading nets on the infestation by aphids [Myzus persicae (Sulzer) and Aphis gossypii Glover (both Hemiptera: Aphididae)] and whiteflies [Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae)], and the incidence of the viral diseases transmitted by these insects, for five consecutive years (2006–2010). These studies were conducted in the semi‐arid Besor region in southern Israel. The plants were grown in ‘walk‐in’ tunnels that were covered by several nets of 35% shading capacity in the range of photosynthetically active radiation. Although the shading nets permit free passage of these pests, the infestation levels of aphids and whiteflies in tunnels covered by either the yellow or pearl nets were consistently 2–3× lower than in tunnels covered by the black or red nets. In accordance with the pest results, when the incidences of Cucumber mosaic virus in pepper grown under the black or red nets ranged between 35 and 89%, they were 2–10× lower under the yellow or pearl nets. Similarly, when the incidences of necrotic Potato virus Y in tomato grown under black or red nets ranged between 42 and 50%, they were 2–3× lower under the yellow or pearl nets. Also, when the incidences of Tomato yellow leaf curl virus in tomato grown under the black or red nets ranged between 15 and 50%, but they were 2–4× lower under the yellow or pearl nets. Putative mechanisms of crop protection achieved by the yellow and pearl nets are discussed.     

Feeding behavior,life history,and virus transmission ability of Bemisia tabaci Mediterranean species (Hemiptera: Aleyrodidae) under elevated CO2

The continuous rise of CO₂ concentrations in the atmosphere is reducing plant nutritional quality for herbivores and indirectly affects their performance. The whitefly (Bemisia tabaci, Gennadius) is a major worldwide pest of agricultural crops causing significant yield losses. This study investigated the plant‐mediated indirect effects of elevated CO₂ on the feeding behavior and life history of B. tabaci Mediterranean species. Eggplants were grown under elevated and ambient CO₂ concentrations for 3 weeks after which plants were either used to monitor the feeding behavior of whiteflies using the Electrical Penetration Graph technique or to examine fecundity and fertility of whiteflies. Plant leaf carbon, nitrogen, phenols and protein contents were also analyzed for each treatment. Bemisia tabaci feeding on plants exposed to elevated CO₂ showed a longer phloem ingestion and greater fertility compared to those exposed to ambient CO₂ suggesting that B. tabaci is capable of compensating for the plant nutritional deficit. Additionally, this study looked at the transmission of the virus Tomato yellow leaf curl virus (Begomovirus) by B. tabaci exposing source and receptor tomato plants to ambient or elevated CO₂ levels before or after virus transmission tests. Results indicate that B. tabaci transmitted the virus at the same rate independent of the CO₂ levels and plant treatment. Therefore, we conclude that B. tabaci Mediterranean species prevails over the difficulties that changes in CO₂ concentrations may cause and it is predicted that under future climate change conditions, B. tabaci would continue to be considered a serious threat for agriculture worldwide.     

Natural enemy impacts on Bemisia tabaci (MEAM1) dominate plant quality effects in the cotton system

1. Plant quality (bottom‐up effects) and natural enemies (top‐down effects) affect herbivore performance. Furthermore, plant quality can also influence the impact of natural enemies. 2. Lower plant quality through reduced irrigation increased the abundance of the cryptic species from the Bemisia tabaci complex [hereafter B. tabaci Middle East Asia Minor 1 (MEAM1)], but not its natural enemies on cotton. It was therefore predicted that lower plant quality would diminish the impact of natural enemies in regulating this herbivore. 3. Over three cotton seasons, plant quality was manipulated via differential irrigation and natural enemy abundance with insecticides. Life tables were used to evaluate the impact of these factors on mortality of immature B. tabaci (MEAM1) over nine generations. 4. Mortality of B. tabaci (MEAM1) was consistently affected by natural enemies but not by plant quality. This pattern was driven by high levels of sucking predation, which was the primary (key) factor associated with changes in immature mortality across all irrigation and natural enemy treatments. Dislodgement (chewing predation and weather) and parasitism contributed as key factors in some cases. Analyses also showed that elimination of sucking predation and dislodgement would have the greatest effect on overall mortality. 5. The top‐down effects of natural enemies had dominant effects on populations of B. tabaci (MEAM1) relative to the bottom‐up effects of plant quality. Effects were primarily due to native generalist arthropod predators and not more host‐specific aphelinid parasitoids. The findings of this study demonstrate the important role of arthropod predators in population suppression and validate the importance of conservation biological control in this system for effective pest control.     

First interception of Bemisia tabaci Mediterranean (Q biotype) in Serbia

The whitefly Bemisia tabaci (Gennadius) is a cosmopolitan insect pest and causes great damage to many agricultural crops by direct feeding, and transmitting many plant viruses causing disastrous effects. The global distribution of B. tabaci was previously investigated, but so far, it has not been confirmed in Serbia. Sampling conducted on plants at three localities in Serbia revealed the presence of three whitefly species, one is B. tabaci Mediterranean (MED) species, a quarantine pest. Additionally, Trialeurodes vaporariorum Westwood and an Aleurodes sp. that was not identified to the species level were also confirmed. The last two are common and widespread species in Serbia. Whitefly collections were made from cabbage, kale and oilseed rape plants (Brassica oleracea, B. oleracea var. sabauda, B. napus, respectively) grown in the field, on sunflower (Helianthus annuus) grown in the greenhouse and on potted hibiscus (Hibiscus sp.) and poinsettia (Euphorbia pulcherrima) plants grown indoors. DNA sequence analysis from a portion of the Cytochrome Oxidase I gene (COI) revealed the presence of B. tabaci MED species, which is considered to be a very important pest worldwide and has been reported from neighbouring countries, however, not yet from Serbia. Bemisia tabaci MED is recorded here for the first time in Serbia. This first interception suggests its introduction with ornamentals grown indoors, with no outdoor reports and that it is not yet spread. This report is an important alert for local authorities to take the necessary steps in monitoring and preventing its possible expansion.     

Density-related sterility in Eretmocerus mundus

While studying the reproductive capacity of Eretmocerus mundus Mercet (Hymenoptera: Aphelinidae) we found that varying numbers of females were sterile. Investigations showed that sterility occurred also in field populations, but at a very low rate. Laboratory sterility was significantly correlated with crowding of the parental females during oviposition. Whitefly hosts from which fertile of sterile females emerged did not differ in size, neither did the hind tibiae of fertile females differ in dimensions from those of sterile ones. Behavior of sterile females differed from that of the fertile ones in several parameters. They exhibited less leg drumming, used the ovipositor more frequently and for shorter durations, and changed more readily from probing to host stinging, and from a number of activities to walking. Altogether, their behavior appeared more restless and caused them to contact more hosts than fertile females. The possibility that the sterility is caused by crowding alone, or by the activity of microorganisms acting under crowded conditions, and the merits of the phenomenon for biological pest control are discussed.     

Host preference and suitability of some selected crops for two biotypes of Bemisia tabaci in Ghana

The economic importance of Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) is mainly due to its wide host range, variable kinds of damage, and great intraspecific variation. The delineation of two African biotypes of this pest has been carried by molecular, ecological, and host‐affiliation approaches, with largely consistent results. However, an understanding of its intricate host–pest interaction is necessary as a basis of its sustainable integrated control. This study investigated the host preference and suitability of cassava and okra biotypes of B. tabaci, based on multiple‐choice landing and oviposition preference assays and stage‐specific survival on eight common whitefly hosts. The cassava biotype significantly preferred cassava, Manihot esculenta, for landing and oviposition, but did not oviposit on okra, Abelmoschus esculentus. The okra biotype preferred okra, oviposited on eggplant, Solanum melongena, tomato, Lycopersicon esculentum, garden egg, Solanum integrifolium, and cowpea, Vigna unguiculata, but did not oviposit on cassava. The okra biotype developed on all hosts except cassava, but only survived marginally on cabbage, Brassica oleracea, and pepper, Capsicum annum var. grosum, while the cassava biotype did not develop on okra, cabbage, or pepper. Thus the observed host acceptance of the two biotypes is wider than earlier reported by host transfer experiments and molecular genetic surveys. Mortality was highest in the first instar nymphal stage, during which total mortality occurred on non‐hosts. Development time was slightly longer on marginal hosts than on the preferred hosts. Cowpea, garden egg, and tomato are additional common hosts of the two biotypes, whose role as reservoir hosts and biotype interbreeding grounds should be investigated further.     

Maternal Inheritance of a Single Somatic Animal Cell Displayed by the Bacteriocyte in the Whitefly Bemisia tabaci

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