Reference List – Bemisia tabaci

Reference List – Bemisia tabaci Q-Biotype

Produced for the Q-subcommittee of the Cross-commodity Working Group

The list was compiled by Steve Naranjo, John Palumbo, and Peter Ellsworth.

1. Guthrie, F., Denholm, I., Devine, G.J. and Nauen, R. 2003. Biological evaluation of spiromesifen against Bemisia tabaci and an assessment of resistance risks. pp. 795-800. In The British Crop Protection Conference: Pests and Diseases. British Crop Protection Council, Farnham, UK. The efficacy of spiromesifen was evaluated against insecticide-resistant 'Q' biotypes of Bemisia tabaci from Israel and Spain. The compound was extremely effective against early instars (LC50s of 0.1-6.2 ppm for 12-day-old nymphs). One Spanish 'Q' type was significantly less susceptible (15-fold). Further selection of that strain with spiromesifen, however, did not select for increasing resistance. Spiromesifen was highly effective against pyriproxyfen- and imidacloprid-resistant whitefly. It also had pronounced transovariole effects on oviposition and egg hatch. Given the current difficulties experienced in the control of 'Q' biotype B. tabaci around the Mediterranean, it is likely that spiromesifen will be a valuable addition to the available chemical options. We consider that the efficacy of this compound is unlikely to be compromised by existing resistance mechanisms.

2. Horowitz, A.R., Denholm, I., Gorman, K., Cenis, J.L., Kontsedalov, S. and Ishaaya, I. 2003. Biotype Q of Bemisia tabaci identified in Israel. Phytoparasitica 31(1): 94-98. The biotype status of samples of the whitefly Bemisia tabaci (Gennadius) collected from several field and greenhouse sites in Israel during 1999-2000 was determined by polyacrylamide gel electrophoresis (PAGE) for general esterases, and by RAPD-PCR using primers of arbitrary sequence. Results of this survey provide the first published evidence for the occurrence of the B. tabaci Q biotype, alongside the more widely distributred B biotype. Based on the collected samples, it appears that both the B and Q biotypes are present in Israel, and that field populations consist of a mixture of the two biotypes. A possible link between B. tabaci biotypes and insecticide resistance is discussed.

3. Horowitz, A.R., Gorman, K., Ross, G. and Denholm, I. 2003. Inheritance of pyriproxyfen resistance in the whitefly, Bemisia tabaci (Q biotype). Arch. Insect Biochem. Physiol. 54(4): 177-186. The inheritance of resistance to pyriproxyfen, an insect growth regulator (a juvenoid, with ovicidal and larvicidal activities), was studied in the whitefly Bemisia tabaci (Gennadius). Two parental strains, both belonging to Q biotype, were assayed with pyriproxyfen; a susceptible strain (ALM-1) originating from Spain and a pyriproxyfen-resistant one (Pyri-R) from Israel. The resistance ratio between the two parental strains was approximately 7,000-fold. Concentration-mortality lines for F1 heterozygous females from reciprocal crosses (SS[female] x R[male] and RR[female] x S[male]) were derived by statistical modelling and proved intermediate to those of the parents. The pooled degree of dominance from both reciprocal crosses was +0.26, indicating that resistance was incompletely or partially dominant. Mortality curves for F2 males produced by virgin F1 heterozygous females displayed a broad plateau at 50% mortality, indicating that resistance to pyriproxyfen in B. tabaci is conferred primarily by a mutant allele at a single locus. The role of arrhenotoky in influencing the mode of inheritance of resistance, and its selection in field populations, is discussed.

4. Horowitz, A.R., Kontsedalov, S., Khasdan, V. and Ishaaya, I. 2005. Biotypes B and Q of Bemisia tabaci and their relevance to neonicotinoid and pyriproxyfen resistance. Arch. Insect Biochem. Physiol. 58(4): 216-225. Resistance monitoring for Bemisia tabaci field populations to the juvenile hormone mimic, pyriproxyfen, was conducted from 1996 to 2003 in commercial cotton fields in two areas of Israel: the Ayalon Valley (central Israel) and the Carmel Coast (northwestern Israel). Although the use of pyriproxyfen ceased in these areas in 1996-1997 (because of the resistance), resistance levels to pyriproxyfen declined to some extent in the fields but remained quite stable, and the susceptibility has not been totally restored. Two strains of B. Tabaci collected from the Ayalon Valley in the late 1999 and 2002 cotton seasons (AV99L, AV02L) were assayed for their susceptibility to pyriproxyfen at F1, and subsequently a line of each strain was kept under controlled conditions without exposure to insecticides. After maintenance of more than 20 generations under laboratory conditions, the resistance to pyriproxyfen in the untreated strains substantially declined. This decline was concurrent with a replacement of Q biotype by B-type under non-insecticidal regimes, apparently B biotype was more competitive than the pyriproxyfen-resistant Q-type. Selection under controlled conditions with neonicotinoids on these B. Tabaci strains resulted in continued pyriproxyfen resistance, predominantly of Q biotype. Based on our data, applications of either pyriproxyfen or neonicotinoids may select for biotype Q, which would survive to a greater degree where these insecticides are applied. (c) 2005 Wiley-Liss, Inc.

5. Jiang, Y.X., de Blas, C., Bedford, I.D., Nombela, G. and Muniz, M. 2004. Effects of Bemisia tabaci biotype on the transmission of tomato yellow leaf curl Sardinia virus (TYLCSV-ES) between tomato common weeds. Spanish J. Agric. Res. 2(1): 115-119. Five weed species, i.e. Datura stramonium, Solanum nigrum, Brassica kaber, Capsella bursa-pastoris and Malva parviflora, were evaluated for their susceptibility to an isolate of TYLCSV from Murcia, Spain (TYLCSV-ES), using the B-, Q- and S-biotypes of B. tabaci as vectors. Both B- and Q-biotypes transmitted TYLCSV-ES from infected tomato to S. nigrum and D. stramonium and vice versa. The transmission efficiency from tomato to these weeds varied from 58.3 to 83.3%. Transmission efficiency from infected weeds to tomato varied from 66.7 to 100.0%. The B- and Q-biotypes did not significantly vary in terms of transmission efficiency from infected tomato to weed plants and from D. stramonium to tomato. However, a significant difference in transmission efficiency from infected S. nigrum plants to tomato was detected between the B- and Q-biotypes. No other tested weed species were infected by TYLCSV-ES. The S-biotype was unable to survive in tomato long enough to acquire or transmit TYLCSV-ES. This biotype could only transmit the virus from S. nigrum to S. nigrum at a very low efficiency. The implications of these results for the epidemiology of TYLCV in the field are discussed.

6. Muniz, M., Jiang, Y.X., Nombela, G., de Blas, C. and Bedford, I. 2004. Short communication. Effect of Bemisia tabaci biotype in the transmission of Tomato Yellow Leaf Curl Sardinia Virus (TYLCSV-ES) between tomato and common weeds. Spanish J. Agric. Res. 2(1): 115-119. The common five weed species Datura stramonium L., Solanum nigrum L., Brassica kaber (DC), Capsella bursapastoris L. and Malva parviflora L., were tested for their susceptibility to an isolate of TYLCSV from Murcia, Spain (TYLCSV-ES), using the B-, Q- and S-biotypes of Bemisia tabaci (Gennadius). Both, B- and Q-biotypes were shown to transmit TYLCSV-ES from infected tomato to S. nigrum and D. stramonium and vice versa. Transmission efficiency from tomato to these weeds varied from 58.3% to 83.3%. Transmission efficiency from the infected weeds back to tomato varied from 66.7% to 100%. No significant difference between the B- and Q-biotypes was found in transmission efficiency from infected tomato to weed plants and from D. stramonium back to tomato. However, a significant difference in transmission efficiency from infected S. nigrum plants to tomato was detected between the B- and Qbiotypes. No other tested weed species were found to be infected by or host TYLCSV-ES. The S-biotype was unable to survive on tomato long enough to acquire or transmit TYLCSV-ES and could only transmit the virus from S. nigrum to S. nigrum at a very low efficiency. The implications of these results for the epidemiology of TYLCV's in the field are discussed. Se analizo la susceptibilidad de las malas hierbas Datura stramonium L., Solanum nigrum L., Brassica kaber (DC), Capsella bursa-pastoris L. and Malva parviflora L. a un aislado del TYLCSV procedente de Murcia, Espana (TYLCSVES), utilizando como vectores los biotipos B, Q y S de Bemisia tabaci (Gennadius). Los biotipos B y Q transmitieron el TYLCSV-ES desde tomate infectado a S. nigrum y D. stramonium y viceversa, con una eficiencia de transmision desde tomate a dichas malas hierbas entre el 58,3% y el 83,3%. La eficiencia de transmision desde las malas hierbas al tomate vario desde el 66,7% al 100%. No se apreciaron diferencias significativas entre los biotipos B y Q respecto a la eficiencia de transmision desde tomate a malas hierbas ni desde D. stramonium a tomate. No obstante, la eficiencia de transmision desde plantas infectadas de S. nigrum a tomate fue significativamente diferente entre los biotipos B y Q. El aislado TYLCSV-ES no fue capaz de infectar a ninguna de las otras especies de malas hierbas utilizadas en este estudio. El biotipo S no pudo sobrevivir en tomate el tiempo suficiente para adquirir o transmitir el TYLCSVES, pudiendo solamente transmitir el virus desde S. nigrum a S. nigrum con una eficiencia muy limitada. Se discuten las implicaciones de estos resultados para la epidemiologia en campo de los virus TYLCV.

7. Muniz, M. and Nombela, G. 2001. Differential variation in development of the B- and Q-biotypes of Bemisia tabaci (Homoptera: Aleyrodidae) on sweet pepper at constant temperatures. Environ. Entomol. 30(4): 720-727. Developmental rates of the B- and Q-biotypes of Bemisia tabaci (Gennadius, 1889) were studied at seven constant temperatures (17, 20, 23, 26, 30, 33, and 35°C) on sweet pepper, Capsicum annuum L. ('Morrón'). The egg incubation period and the times required to complete development at all immature stages decreased with increasing temperature up to 33°C, but at 35°C were found to be greater than at 33°C. The relationships between developmental rate of B. tabaci and temperature were influenced by the insect biotype. The lower and upper developmental thresholds as well as the optimal temperatures and thermal constant for the preoviposition period and all immature stages were estimated by fitting the observed developmental rates versus temperature with a nonlinear model and two linear models. For all stages, graphs obtained by plotting the reciprocal of development times against temperature could be described by the modification 2 of the Logan's model. The simple linear model tT = K+ct suffices for predicting B- and Q-biotype phenologies on sweet pepper for the temperature range of 17-33°C. The shortest developmental times as well as the lowest developmental thresholds and thermal constant were mostly obtained with the Q-biotype. Overall, the most favorable temperature range appeared to be 31-33°C. Mean generation times (adult-adult) ranged from 17 d (Q-biotype) and 18 d (B-biotype) at 33°C to 49 d (B-biotype) and 46 d (Q-biotype) at 17°C.

8. Muniz, M., Nombela, G. and Barrios, L. 2002. Within-plant distribution and infestation pattern of the B- and Q-biotypes of the whitefly, Bemisia tabaci, on tomato and pepper. Entomol. Exp. Appl. 104(2-3): 369-373. Short communication – no abstract

9. Nauen, R. and Denholm, I. 2005. Resistance of insect pests to neonicotinoid insecticides: Current status and future prospects. Arch. Insect Biochem. Physiol. 58(4): 200-215. The first neonicotinoid insecticide introduced to the market was imidocloprid in 1991 followed by several others belonging to the some chemical class and with the some mode of action. The development of neonicotinoid insecticides has provided growers with invaluable new tools for managing some of the world's most destructive crop pests, primarily those of the order Hemiptera (aphids, whiteflies, and planthoppers) and Coleoptera (beetles), including species with a long history of resistance to earlier-used products. To date, neonicotinoids have proved relatively resilient to the development of resistance, especially when considering aphids such as Myzus persicae and Phorodon humuli. Although the susceptibility of M. Persicae may vary up to 20-fold between populations, this does not appear to compromise the field performance of neonicotinoids. Stronger resistance has been confirmed in some populations of the whitefly, Bemisia tabaci, and the Colorado potato beetle, Leptinotarso decemlineata. Resistance in B- and Q-type B. Tabaci appears to be linked to enhanced oxidative detoxification of neonicotinoids due to overexpression of monooxygenases. No evidence for target-site resistance has been found in whiteflies, whereas the possibility of target-site resistance in L. Decemlineata is being investigated further. Strategies to combat neonicatinoid resistance must take account of the cross-resistance characteristics of these mechanisms, the ecology of target pests on different host plants, and the implications of increasing diversification of the neonicotinoid market due to a continuing introduction of new molecules. (c) 2005 Wiley-Liss, Inc.

10. Nauen, R., Stumpf, N. and Elbert, A. 2002. Toxicological and mechanistic studies on neonicotinoid cross resistance in Q-type Bemisia tabaci (Hemiptera : Aleyrodidae). Pest Manag. Sci. 58(9): 868-875. The tobacco whitefly, Bemisia tabaci Gennadius (Homoptera: Aleyrodidae) is a serious pest in numerous cropping systems and has developed a high degree of resistance against several chemical classes of insecticides. One of the latest group of insecticides introduced to the market were the neonicotinoids (chloronicotinyls), acting agonistically on insect nicotinic acetylcholine receptors. Resistance to neonicotinoid insecticides has recently been shown to occur, especially in Q-type B. tabaci in some places in Almeria, Spain, whereas control of B-type B. tabaci in many other intense cropping systems worldwide has remained on high levels. Our study revealed that neonicotinoid-resistant Q-type strains from Almeria were often more than 100-fold less susceptible to thiamethoxam, acetamiprid and imidacloprid when tested in discontinuous systemic laboratory bioassays. The resistance factors were generally 2- to 3-fold lower in leaf-dip bioassays. In addition to the Spanish stra ins, we obtained two other highly neonicotinoid-cross-resistant B. tabaci greenhouse populations, one from Italy (December 1999) and one from Germany (June 2001). A molecular diagnostic analysis revealed that both strains also belong to the (Spanish) subtype Q of the B. tabaci species complex. The resistance levels of Q-type whitefly strains derived from Almeria greenhouses in 1999 remained stable for at least two years, even when maintained in the laboratory without any selection pressure. The biochemical mechanisms conferring resistance to neonicotinoids have not yet been elucidated in detail, but synergist studies suggested a possible involvement of microsomal monooxygenases. Furthermore, we checked two Almerian strains of B. tabaci isolated in 1998 and 1999 and demonstrated that neonicotinoid resistance is not due to an altered [3H]imidacloprid binding site of nicotinic acetylcholine receptors.

11. Nombela, G., Beitia, F. and Muniz, M. 2001. A differential interaction study of Bemisia tabaci Q-biotype on commercial tomato varieties with or without the Mi resistance gene, and comparative host responses with the B-biotype. Entomol. Exp. Appl. 98(3): 339-344. Short communication – no abstract

12. Pascual, S., Aviles, M., Nombela, G., Muniz, M. and Beitia, F. 2000. Development of Bemisia tabaci (biotype Q) on tomato cultivars with/without the Mi gene. Med. Fac. Landbouww. Univ. Gent 65(2a): 291-292. Short communication – no abstract

13. Pascual, S. and Callejas, C. 2004. Intra- and interspecific competition between biotypes B and Q of Bemisia tabaci (Hemiptera: Aleyrodidae) from Spain. Bull. Entomol. Res. 94(4): 369-375. Biotypes B and Q of Bemisia tabaci (Gennadius), collected from the islands of Tenerife and Majorca respectively, were exposed to competition conditions on tomato cv. Marmande in the laboratory. Both biotypes were established in single and mixed cultures at different densities. Increased mortality of biotype Q females and immature instars was observed together with a lower rate of fecundity and progeny size compared to biotype B, when reared in single or mixed cultures. The female:male sex ratio of F1 individuals of biotype Q was higher in single than in mixed cultures. However, the sex ratio of F1 individuals of biotype B was the same in single and mixed cultures, suggesting reproductive interference. Whitefly density did not affect interspecific interactions. It had a moderate effect on developmental rate of both biotypes, and on mortality of immature instars and progeny size of biotype B only. The results indicate that under laboratory conditions the studied biotype B should displace biotype Q.

14. Pascual, S., Nombela, G., Avilés, M. and Muñiz, M. 2003. Induced resistance in tomato to whitefly Bemisia tabaci by Bion(R). Bull. OILB/SROP (IOBC/WPRS) 26(10): 61-64. Chemical elicitors can induce plant resistance to insects and other pests in susceptible plants. They include benzo [1,2,3] thiadiazole-7-carbothioic acid-S-methyl ester (BTH), which is the active ingredient in the Syngenta plant activator Bion. Induced plant resistance to the B and Q biotypes of Bemisia tabaci after foliar application of Bion to tomato cv. Marmande plants was evaluated under controlled conditions. In a free-choice experiment, adult Q-biotype B. tabaci significantly preferred control plants to plants sprayed with Bion at 0.2 g/l. In consequence, the number of eggs laid on treated plants was lower, but female fecundity was not affected. After 23 days, a decrease in the number of empty pupal cases was also observed on plants treated with Bion at 0.2 g/l. The effect produced by Bion applied at 0.1 g/l was not significant. In a no-choice assay, only one leaflet from each tomato plant was treated with either 1 g Bion/litre or water (control plants). A clip-cage con taining 5 B. tabaci females (biotype B) was attached to each treated leaflet and to another non-treated leaflet from every plant. After 16 days, the total number of immature insects (eggs+L1+L2) on Bion-treated leaflets was significantly lower than on the water-treated leaflets from the control plants. This difference was mostly due to the number of L1 larvae. The acquired resistance seemed to be very localized (LAR) given the differences between Bion-treated and non-treated leaflets on the same plants, while no differences were observed between Bion-treated and control plants in the case of non-treated leaflets.

15. Rauch, N. and Nauen, R. 2003. Identification of biochemical markers linked to neonicotinoid cross resistance in Bemisia tabaci (Hemiptera: Aleyrodidae). Arch. Insect Biochem. Physiol. 54(4): 165-176. The whitefly, Bemisia tabaci (Hemiptera: Aleyrodidae), is a serious pest in many cropping systems world-wide and occurs in different biotypes. The most widespread one is the B-type, whereas the Q-biotype is nowadays still mostly restricted to Southern Spain. Neonicotinoid cross-resistance is known at a high level in Q-types from Spain and individual samples collected in Italy and Germany. Now we detected for the first time high neonicotinoid cross-resistance in a B-type from Israel. Target site resistance to imidacloprid using [3H]imidacloprid in nicotinic acetylcholine receptor (nAChR) binding assays could not be detected in any of these highly resistant strains. The impact of metabolizing enzymes such as esterases, glutathione S-transferases [glutathione transferase], and cytochrome P450-dependent monooxygenases in neonicotinoid resistance was studied biochemically with artificial substrates. Monooxygenase activity was increased 2-3-fold in moderately resistant strains (RF ~30) and even 5-6-fold in highly resistant strains (RF ~1,000). Only monooxygenase activity correlated with imidacloprid, thiamethoxam and acetamiprid resistance and, therefore, monooxygenases seem to be the only enzyme system responsible for neonicotinoid resistance in B. tabaci Q- and B-types. The oxidative degradation of imidacloprid in resistant Q-type strains could be confirmed by metabolism studies of [14C]imidacloprid in vivo. Five-hydroxy-imidacloprid could be detected as the only main metabolite. The insecticidal activity and binding affinity to nAChR of this compound was 10 times lower than imidacloprid itself in B. tabaci.

16. Urbaneja, A. and Stansly, P.A. 2004. Host suitability of different instars of the whitefly Bemisia tabaci 'biotype Q' for Eretmocerus mundus. Biocontrol 49(2): 153-161. Eretmocerus mundus Mercet is a parasitoid of Bemisia tabaci (Genn.) indigenous to the Mediterranean and is used commercially for augmentative biological control in Spain and elsewhere. A better understanding of the suitability of different host instars would help optimize production and field application. Incidence of parasitism, development time, survivorship and sex ratio were evaluated when different nymphal instars of the sweetpotato whitefly Bemisia tabaci biotype 'Q' were offered for parasitization. Experiments were conducted on sweet pepper at 25 degrees C, 75% RH and 16:8 (L:D) photoperiod. E. mundus oviposited in all nymphal instars of B. tabaci except the mature 4th instar or pharate adult (previously designated, 'pupa'). Incidence of parasitism was greatest (33.8+or-5.1 parasitized nymphs) and development time shortest (14.1+or-0.1 d) when oviposition occurred under 2nd and 3rd instar nymphs compared to 1st or 4th instars. Survivorship (85%) and offspring sex ratio (39.8% female) did not differ statistically for parasitoids developing in whiteflies that were parasitized as different instars. Although 2nd and 3rd instars were clearly the most favorable host stage for E. mundus, its capacity to parasitize and develop on a wide range of host stages is a favorable characteristic for both rearing and field application.

17. Urbaneja, A., Stansly, P.A., Beltrán, D., Sánchez, E. and Gallego, A. 2003. Life history of Eretmocerus mundus Mercet (Hymenoptera: Aphelinidae) on Bemisia tabaci biotype "Q" (Homoptera: Aleyrodidae) using sweet pepper and tomato. Bull. OILB/SROP (IOBC/WPRS) 26(10): 67. E. mundus is native to the Mediterranean region where it spontaneously parasitizes B. tabaci in greenhouse-grown fruiting vegetables. Fecundity on tomato and pepper was evaluated by placing newly emerged couples (n=15) of E. mundus on leaf discs infested with second instar B. tabaci, the preferred stage, maintained at 25 deg C and changed daily until the female died. All whitefly nymphs were observed for host feeding. Parasitoid eggs were counted. Adult longevity was estimated at 10.1 plus or minus 1.0 days (mean plus or minus SEM) in pepper and 7.3 plus or minus 0.81 days in tomato. Fecundity (number of hosts) was estimated 171.1 plus or minus 22.8 per female in pepper and 147.8 plus or minus 13.5 in tomato. Host feeding incidence was 15.6 plus or minus 0.98 nymphs per female in pepper and 10.7 plus or minus 1.3 in tomato. No significant differences were detected in the duration of life stages between tomato and sweet pepper. Preimaginal survivourship estimated in clip cages starting with 66 eggs in pepper and 59 eggs in tomato was 81.0 and 64.4%, respectively. Most of the difference were due to 17% mortality during the pupal stage in tomato possibly due to leaf degradation and not seen in pepper. Ro in pepper was estimated at 67.50 plus or minus 8.71 (mean plus or minus SD) which was significantly greater than 47.00 plus or minus 4.02 in pepper. However, generation time (T) was also significantly greater in pepper (19.40 plus or minus 0.46) than in tomato (18.10 plus or minus 0.36). As a consequence of these two opposing factors, the estimate of intrinsic rate of increase (rm) was not statistically different in pepper 0.218 plus or minus 0.005 than in tomato (0.214 plus or minus 0.004). These values are well above those reported for B. tabaci on any crop indicating the potential of E. mundus to control this pest.

Guirao, P., Belitia, F. and Cenis, J.L. 1997. Biotype determination of Spanish populations of Bemisia tabaci (Hemiptera: Aleyrodidae). Bull. Entomol. Res. 87(6): 587-593.

18. Muniz, M. 2000. Host suitability of two biotypes of Bemisia tabaci on some common weeds. Entomol. Exp. Appl. 95(1): 63-70. Significant differences in some reproductive parameters of the B and Q biotypes of Bemisia tabaci (Gennadius) with regard to four species of winter weeds were determined in a no-choice assay. The highest fecundity (eggs) and fertility (pupae and adults) were obtained with Malva parviflora L. as host, followed by Capsella bursa-pastoris L., Brassica kaber (DC) and Lactuca serriola L. The percentage of adult emergence (from egg to adult) was significantly higher (P < 0.001) with M. parviflora, C. bursa-pastoris and B. kaber than with L. serriola. Except on L. serriola, the mean values of the reproductive parameters for the Q-biotype were significantly (P < 0.05) greater than those for the B-biotype. On the other hand, in choice experiments with summer weeds, both B- and Q-biotypes preferred Datura stramonium L. and Solanum nigrum L. to Amaranthus retroflexus L., Chenopodium album L. and Echinochloa crus-galli L. Significantly more males and females, and more pupae and empty pupal cases per plant were found on D. stramonium than on S. nigrum. Adult abundance on A. retroflexus, C. album and E. crus-galli plants was very low. At a constant temperature of 26 ± 1°C, the Q-biotype developed significantly faster than the B-biotype on S. nigrum and D. stramonium. Both biotypes required, for this development, significantly more days on D. stramonium than on S. nigrum. These results suggest that it is important to suppress the growth of M. parviflora, C. bursa-pastoris, B. kaber, D. stramonium and S. nigrum in order to avoid the risk of further expansion of whitefly populations where these weeds and both B- an Q-biotypes are present.

19. Cervera MT, Cabezas JA, Simon B, Martinez-Zapater JM, Beitia F, Cenis JL., Bull Entomol Res. 2000 Oct;90(5):391-6. Genetic relationships among biotypes of Bemisia tabaci (Hemiptera: Aleyrodidae) based on AFLP analysis. Genetic similarities between 13 samples belonging to nine reference biotypes and two field populations of Bemisia tabaci (Gennadius), one field population of B. medinae Gomez-Menor and another of B. afer Priesner & Hosny, were evaluated using amplified fragment length polymorphism (AFLP) markers. The results indicate that B. tabaci biotypes can be grouped together with a minimum similarity coefficient of 0.32 and separated from the two other species with a similarity coefficient of 0.07. Bemisia tabaci biotypes were grouped in four clusters which comprised: (i) Near East and Indian subcontinent biotypes; (ii) B and Q biotypes plus a Nigerian population from cowpea; (iii) New World A biotype; and (iv) S biotype and a Nigerian population from cassava. These results were consistent with a previous grouping of biotypes based on RAPD-PCR analysis. The AFLP assay allowed the scoring of a total of 354 polymorphic bands in two reaction events with the use of two primer combinations.

20. D. Boscoa, G. Masona, b and G. P. Accotto, b, TYLCSV DNA, but not infectivity, can be transovarially inherited by the progeny of the whitefly vector Bemisia tabaci (Gennadius). The transovarial transmission of two species of begomovirus, Tomato yellow leaf curl virus (TYLCV) and Tomato yellow leaf curl Sardinia virus (TYLCSV), through generations of Bemisia tabaci of the B and Q biotypes has been investigated. Different life stages of the progeny of viruliferous female whiteflies have been analysed by PCR detection of viral DNA and infectivity tests. Our results indicate that TYLCSV DNA can be detected in eggs and nymphs, and to a lesser extent adults, of the first-generation progeny. Infectivity tests using a large number of adult progeny of the first, second, and third generation indicate that even when viral DNA is inherited, infectivity is not. For TYLCV, neither viral DNA nor infectivity were associated with the progeny of viruliferous female whiteflies. Because the inherited viral DNA is unable to give rise to infections, the transovarial transmission of TYLCSV DNA appears to have no epidemiological relevance.

21. Delatte H, Reynaud B, Granier M, Thornary L, Lett JM, Goldbach R, Peterschmitt M. Bull Entomol Res. 2005 Feb;95(1):29-35. A new silverleaf-inducing biotype Ms of Bemisia tabaci (Hemiptera: Aleyrodidae) indigenous to the islands of the south-west Indian Ocean. Following the first detection of tomato yellow leaf curl virus (TYLCV) from Reunion (700 km east of Madagascar) in 1997 and the upsurge of Bemisia tabaci (Gennadius) on vegetable crops, two genetic types of B. tabaci were distinguished using RAPD-PCR and cytochrome oxidase I (COI) gene sequence comparisons. One type was assigned to biotype B and the other was genetically dissimilar to the populations described elsewhere and was named Ms, after the Mascarenes Archipelago. This new genetic type forms a distinct group that is sister to two other groups, one to which the B biotype is a member and one to which the Q biotype belongs. The Ms biotype is thought to be indigenous to the region as it was also detected in Mauritius, the Seychelles and Madagascar. Both B and Ms populations of B. tabaci induced silverleaf symptoms on Cucurbita sp., and were able to acquire and transmit TYLCV. Taken together these results indicate that the Ms genetic type should be considered a new biotype of B. tabaci.

22. Ishaaya I. Arch Insect Biochem Physiol. 2005 Apr;58(4):191. Novel insecticides: Modes of action and resistance mechanism. Efforts have been made during the past three decades to develop insecticides with selective properties that act specifically on biochemical sites present in particular insect groups, but whose properties differ from other insecticides. This approach has led to the discovery of compounds that affect the hormonal regulation of molting and developmental processes in insects, e.g., ecdysone agonists (tebufenozide and methoxyfenozide), juvenile hormone mimics (pyriproxyfen and fenoxycarb), and chitin synthesis inhibitors (benzoylphenyl ureas and buprofezin). In addition, compounds that selectively interact with the insect nicotinic acetylcholine receptor such as imidacloprid, acetamiprid, and thiamethoxam have been introduced for the control of aphids, whiteflies, and other insect species.In this issue, we report on some new insecticides that fit the current approach of pest management programs, such as the new non-steroidal ecdysone agonist THQ [1-aroyl-4-(arylamino)1,2,3,4-tetrahydroquinoline], which acts preferentially against mosquitoes with no appreciable effect on other insect groups or mammals. The mode of action of this compound, along with its selectivity, is discussed in detail in the report of Palli et al. Another novel compound reported in this issue is pyradalyl (S-1812), which was found to act selectively on lepidopterans and thrips. In laboratory assays, pyradalyl was found to act on insect cell lines with no appreciable effect on mammal cell lines. The potential use of this compound in agricultural systems is discussed by Isayama et al.Three reports in this issue deal with resistance mechanisms and resistance management of novel insecticides. Nauen et al. present an up-to-date review on insect resistance mechanisms to neonicotinoids and ways to optimize their use in pest management programs. Horowitz et al. report on Bemisia tabaci biotypes B and Q and their resistance to neonicotinoids and pyriproxyfen. One of the most striking findings in their report is that the Q biotype develops resistance to pyriproxyfen and neoicotinopid faster than biotype B, while the latter exhibits better fitness. The practical implications of these findings are discussed. In another report, Ishaaya et al. present a study detailing the toxicity and cross-resistance of selected biorational insecticides. Their findings indicate that no appreciable cross-resistance was observed between the benzoylphenyl urea, novaluron, the juvenile hormone mimic, pyriproxyfen, and the neonicotinoids, acetamiprid and imidacloprid. Hence, these compounds could be used, in alternation, as components in insecticide resistance management programs.

23. Moya A, Guirao P, Cifuentes D, Beitia F, Cenis JL. Mol Ecol. 2001 Apr;10(4):891-7. Genetic diversity of Iberian populations of Bemisia tabaci (Hemiptera: Aleyrodidae) based on random amplified polymorphic DNA-polymerase chain reaction. The genetic structure of six Iberian populations of the whitefly Bemisia tabaci, two of them biotype Q, one biotype B, and the other three a mixture of both, has been studied using random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR). A total of 336 individuals was completely discriminated by means of 234 scored bands. Separate analyses of molecular variance of haploid males and diploid females using the pairwise number of differences between haplotypes showed that biotypes contribute significantly more to the observed variability than populations within biotypes. On average, gene flow between two biotypes of the same population is lower than between populations of identical biotypes. On the basis of these results and the nondetection under natural conditions of a single hybrid, we consider that both biotypes are genetically isolated under the ecological conditions prevailing in the south Iberian Peninsula. All populations of biotype Q presented similar values of intrapopulational diversity, which were higher than the values shown by populations of biotype B.