The development of a B-biotype Bemisia tabaci Italian colony was studied on bean at 9 constant temperatures (15, 16, 17, 20, 23, 26, 29, 32, 35°C). The developmental time from egg-to-adult varied from 70 days at 16°C to 22 at 26°C and higher temperatures. A thermal requirement for egg-to-adult development of 307 day-degrees was calculated, based on a lower developmental threshold of 11.53°C. The survival of egg, nymph and adult whiteflies was investigated at 0, 2, 4, and 6°C on broad bean for periods of 1-8 days. The adult was the most cold-sensitive stage, while the egg and nymph showed a similar level of cold resistance. The effect of sub-lethal cold stress of 4-8 days at 4°C on eggs and nymphs was studied. After exposure to low temperatures, whiteflies needed longer developmental times, from 5 to 8 days more. The presence of B. tabaci under outdoor conditions in Italy was investigated with field surveys and correlated with climatic data; the whitefly species was found in open field conditions only south of the 41° parallel, in areas characterised by less than 5 frost days per winter and by annual mean temperatures >16°C.
Encarsia bimaculata (Heraty & Polaszek) is an abundant parasitoid of Bemisia tabaci in southern China. The effects of constant temperatures on a range of life history traits, including development, survival of immatures, longevity and reproduction of adults, were studied in the laboratory. The developmental period from egg to adult ranged from 34.3 ± 0.4 d at 20°C to 8.7 ± 0.6 d at 32°C, A total of 181.4 ± 2.4 degree-days were required to complete development with a lower developmental threshold of 11.6 ± 0.3°C. The survivorship of E. bimaculata from 2nd instar to adult varied from 81.3 ± 1.7% at 20°C to 91.0 ± 1.8% at 26°C. Average adult female longevity was 8.4 ± 0.7 d at 20°C and 5.4 ± 0.4 d at 32°C, and daily production of offspring peaked at 29°C with 4.5 offspring per female. The maximum oviposition occurred three days after adult emergence at 23, 26, 29 and 32°C, and four days at 20°C. Total number of offspring produced per female varied from 24.3 ± 2.0 at 32°C to 29.3 ± 2.9 at 20°C. The maximum intrinsic rate of increase (rm) was 0.2163 ± 0.013 at 29°C, followed by 0.2062 ± 0.022 at 32°C. Results indicate that E. bimaculata reaches its maximum biological potential at temperatures ranging from 26°C to 32°C with 29°C being the optimal temperature.
Bemisia tabaci (Gennadius) is a worldwide pest of vegetable, ornamental and field crops. Biotype B of B. tabaci, which is economically most important of the biotypes, is distinct from all other biotypes (non-B biotypes). Fourteen populations of B. tabaci were collected from different localities and host plants in the Chinese mainland and Taiwan, namely TWYDH (tassel flower, Taiwan), HNYC (tobacco, Hainan), GXNG (pumpkin, Guangxi), GDYPH (poinsettia, Guangdong), GDBSM (croton, Guangdong), GDFS (Chinese hibiscus, Guangdong), SHYPH (poinsettia, Shanghai), FJGS (sweet potato, Fujian), SDFQ (tomato, Shandong), BJXHL (squash, Beijing), XJQZ (eggplant, Xinjiang), XJYPH (poinsettia, Xinjiang), XJJM (abutilon, Xinjiang) and XJMH (cotton, Xinjiang). The internally transcribed spacer 1 sequences (ITS1) of ribosomal DNA of B biotype and other biotypes were sequenced and analyzed. The B biotype-specific primers were then designed for rapid identification of B biotype of B. tabaci. The results show that the diagnostic primer only gave a positive result with the B biotype. This is the first report of a rapid means of identifying B. tabaci B biotype using a diagnostic primer based on ribosomal DNA. This protocol is especially useful for identifying the B biotype in Bemisia populations consisting of several biotypes.
We studied the predation behaviour of the "hunter fly" (Coenosia attenuata Stein) in the laboratory and greenhouse. In the laboratory, which was conducted at 25°C at 60-80% RH, with a 16L : 8D photoperiod, we examined the functional response of this species to three different pests, namely the sciarid fly (Bradysia sp.), the tobacco whitefly (Bemisia tabaci) and the leaf miner Liriomyza trifolii. In the greenhouse, we studied the population dynamics of the predator and its prey on pepper and water melon crops grown in southern Spain. Adult hunter flies were found to exhibit a type I functional response to adult sciarid flies and whiteflies, but a type II response to adult leaf miners. The type II response was a result of the greater difficulty in capturing and handling leaf miners compared to the other two species. The dynamics of the predator-prey interaction in the greenhouse revealed that the predator specializes mainly on adult sciarids and that the presence of the other prey can be supplemental, but is never essential for survival of the predator; this, however, is crop-dependent. The results on the dynamics of the predator-prey systems were obtained through a known population dynamics model with modifications.
Stable reference genes (RGs) determine the reliability of quantitative polymerase chain reaction (qPCR) analyses and it is recommended that different reference genes are used for different types of DNA and tissues. The present study aimed to screen for stable RGs for the qPCR analysis of the immune responses of the whitefly Bemisia tabaci to the Wolbachia wMel strain from Drosophila melanogaster. A total of eight candidate RGs were evaluated using five different methods, i.e., Coefficient of Variation analysis, GeNorm, NormFinder, BestKeeper and ΔCt. The stability of these RGs was assessed for both genomic DNA (gDNA) and complementary DNA (cDNA). The results indicate that β-actin (Actin) and elongation factor 1 alpha (EF-1α) were the most stable RGs for gDNA, whereas 18S rRNA (18S) and glyceraldehyde phosphate dehydrogenase (GAPDH) were the least stable; in contrast, Actin and GAPDH were the most stable for cDNA, whereas RPL29 and ATPase were the least stable. The effectiveness of the most stable RGs was then validated against the least stable using qPCR analysis of the titre of wMel (gDNA) and the transcriptional responses of the antimicrobial peptide Alo-3-like and the phosphatidylinositol-bisphosphate 3-kinase catalytic subunit delta isoform (cDNA) to wMel transfection. The results support the notion that reliable RGs are essential for a qPCR analysis of samples of both gDNA and cDNA.
The ladybird, Serangium japonicum (Coleoptera: Coccinellidae), is one of the most important predators of whiteflies in China, however, the suitability of different kinds of prey and nutritional requirements of this predator are poorly studied. The objectives of the present study were to investigate the pre-imaginal development, percentage survival of immatures, adult longevity and fecundity of S. japonicum when reared on two different species of prey, mixed ages of the cotton whitefly Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) biotype-B (i.e., eggs and nymphs) and green peach aphid Myzus persicae (Sulzer) (Hemiptera: Aphididae) in order to quantify their relative suitability as prey under laboratory conditions of 25 ± 1°C, 50 ± 10% RH and a photoperiod of 16L : 8D. The results of this study indicate that the total developmental period (from egg to adult) was shorter when they were fed on B. tabaci (18.29 ± 0.13 days) than on M. persicae (19.85 ± 0.22 days). The percentage survival of the immatures, growth index, development rate, adult fresh weight, fecundity and percentage of eggs hatching were higher and the pre-oviposition period was significantly shorter when S. japonicum were fed on B. tabaci than on M. persicae. In contrast, there was no significant difference in their longevity and oviposition period when fed on B. tabaci and M. persicae. The results indicate that as a diet for S. japonicum M. persicae is inferior to B. tabaci. This is the first record of S. japonicum being able to complete its development feeding exclusively on M. persicae. Since B. tabaci and M. persicae often simultaneously occur in vegetable fields, these results indicate that it is likely that S. japonicum could be utilized to control mixed populations of aphids and whiteflies, and furthers our understanding of ladybird population dynamics in the field in relation to the availability of different species of prey.