Bemisia afer (Priesner & Hosny)

Malumphy, Christopher, Walsh, Katherine, Suarez, Belen, Collins, Dominique W. & Boonham, Niel, 2009, Morphological and molecular identification of all developmental stages of four whitefly species (Hemiptera: Aleyrodidae) commonly intercepted in quarantine, Zootaxa 2118, pp. 1-29 : 7-11

Bemisia afer (Priesner & Hosny)

( Figs 5–14 )

B. afer was originally described by Priesner & Hosny (1934) in the genus Dialeurodoides , from specimens collected on sycamore fig ( Ficus sycamorus ) and Lawsonia alba in Egypt. It is broadly polyphagous, feeding on host plants belonging to 46 genera in 22 families ( Martin, 1999; Mound & Halsey, 1978). It occurs widely in the warmer parts of the world and has recently established in the UK ( Malumphy, 2003). It is a serious whitefly pest of field crops in sub-Saharan Africa and China and is implicated in plant-pathogenic virus transmission.

Specimens measured

GAMBIA: (intercepted in UK), on Manihot esculenta , 7.iii.2001, PHSI, CSL2011121 (3 first, 7 second, 3 third instars and 3 adult females). ITALY: (intercepted in UK) on Laurus nobilis , 17.v.2002, PHSI, CSL2022987 (1 third instar); (intercepted in UK, plants imported via Belgium), on L. nobilis , 15.x.1999, PHSI, CSL996362 (7 eggs, 8 first, 1 second and 8 third instars), 15.xi.1999, PHSI, CSL997270 (2 adult females), 21.i.2000, PHSI, CSL2000326 (9 third instars), 21.iv.2000, PHSI, CSL2003927 (4 adult males and 1 adult female); (intercepted in UK, plants imported via Belgium, cultured at CSL under licence), on L. nobilis , 23.i.2001, CSL2010267 (2 third instars), 28.v.2001 (6 first and 1 second instar), 4.vii.2001 (2 first, 3 second and 2 third instars), 2001 (2 eggs, 1 second instar, 1 adult male and 2 female adults). UGANDA: Entebbe (cultured at the Natural Resources Institute (NRI) and CSL under licence), on M. esculenta , 13.xii.2002 (7 first, 2 second and 4 third instars). UNITED KINGDOM: London, Chelsea Physic Gardens, on L. nobilis , 27.vii.2000, PHSI, CSL2004878 (7 eggs, 7 instar and 2 second instars).

Oviposition pattern varies considerably. Eggs are most commonly scattered, or in small groups of up to five, on the lower surface of the foliage. On smooth leaves, for example L. nobilis , they may be laid in irregular rows, partial circles or complete circles of approximately 20 eggs. The chorion is smooth and shiny with little wax evident. Each egg is erect and firmly attached to the leaf surface by a slender peduncle extending from the base of the egg, inserted into the plant tissue. The egg bends slightly as it matures. After hatching, the egg remains upright and is a distinctive golden brown colour. Hatched eggs can remain attached to the plant for many months. Length 220 microns (196–248 microns), width 131 microns (108–150 microns), 1.68 (1.55–1.93) times longer than wide. Peduncle length 24 microns and width is 12 microns (10–12 microns).

FIRST-INSTAR LARVA ( Fig. 6 )

Habitus. Scale-like, pale translucent yellow, becoming slightly darker as they mature. Reddish eye spots and two yellow abdominal mycetomes clearly visible. A narrow band of white wax is present around the margin. The majority of larvae settle to feed within one cm from their eggs.

Margin. Outline ovoid, lozenge-shaped; length 288 microns (204–317 microns) and width 188 microns (134–212 microns), 1.53 (1.26–1.75) times longer than wide. With 16 pairs of well-developed setae: MS14 pair length 60 microns (38–76 microns); CS length 58 microns (30–72 microns); ratio CS/MS14 = 0.97 (0.71–1.07).

Dorsum. Some slide-mounted specimens are a pale grey in colour. Chaetotaxy comprises paired ASS length 16 microns (9–22 microns); CeS length 3 microns (1–7 microns); 1 AS length 3 microns (1–5 microns); and 8 AS length 2 microns (1–5 microns). Cephalic tubercles usually weakly developed, oval to subrectangular. Vasiform orifice almost quadrate and closed behind, length 30 microns (22–33 microns). Lingula head spinulose with one or two pairs of stout setae, half-covered by the operculum. Operculum and lingula pigmented light brown in some specimens.

Ve n t e r. Legs well developed. Fore coxae with short spine, mid and hind coxae with long setae and short spines. Tibia-tarsi distinctly spinose. Antennae long and slender, length 76 microns (63–85 microns). Abdominal setae placed mid vasiform orifice. Cuticle fine, diaphanous.

SECOND-INSTAR LARVA ( Fig. 7 )

Habitus. Distribution similar to first instars. Scale-like, similar in appearance to first instar but larger and more transparent.

Margin. Outline ovoid, widest across mesothoracic legs; length 385 microns (328–418 microns), width 274 microns (224–296 microns), 1.41 (1.34–1.48) times longer than wide. AMS pair fine, acute, length 9 microns (3–16 microns); PMS fine, acute, length 15 microns (10–25 microns); CS stout, length 50 microns (44–72 microns). Ratio CS/PMS = 3.49 (1.92–4.91). Margin evenly, faintly crenulate; slightly indented at thoracic opening and crenulations may be slightly more conspicuous.

Dorsum. Chaetotaxy comprises paired CeS, length 16 microns (2–60 microns); 1 AS, 18 microns (2–62 microns); and 8 AS, 8 microns (3–25 microns). The dorsal setae exist in two distinct states: minute (2–8 microns) or well developed (20–62 microns). The setal pairs most frequently well-developed are CeS and 1 AS, and to a lesser extent 8 AS. There are approximately 13 pairs of geminate pore/porettes aligned subdorsally in two longitudinal rows. Abdominal segmentation rather faintly marked, medially and sub-medially. Abdominal segment VII reduced medially, pockets marked. Vasiform orifice rectangular or almost triangular, sides concave, closed behind, length 41 microns (36–44 microns); inset from posterior margin by less than its own length, half occupied by the operculum with most of the lingula head visible. Lingula head spinulose with pair of stout setae. Operculum and lingula may be pigmented light brown.

Ve n t e r. Legs roughly triangular, each with a subcircular apical pad. Antennae small and slender, laterad, length 25 microns (20–28 microns). Abdominal setae placed mid-vasiform orifice. Cuticle fine, diaphanous.

THIRD-INSTAR LARVA ( Fig. 8 )

Habitus. Distribution similar to first and second instars. Ovoid, variable in colour from translucent to yellow and occasionally with four longitudinal dark patches.

Margin. Body elongate-oval, length 618 microns (540–732 microns), width 458 microns (380–552 microns), 1.36 (1.18–1.54) times longer than wide, generally widest across the meso-coxae. Three pairs of acute, marginal setae: AMS pair fine, length 12 microns (6–24 microns); PMS pair fine, length 18 microns (10–30 microns); CS pair stout, length 74 microns (64–90 microns); ratio CS/PMS = 4.25 (3.00–6.67). Margin fine to very finely crenate. Tracheal pore area indented slightly and crenulations often more pronounced.

Dorsum. Chaetotaxy comprises paired CeS, length 5 microns (3–10 microns); 1 AS, length 5 microns (3–10 microns); and 8 AS, length 5 microns (3–8 microns). 8 AS usually occurs on the lateral margin of the vasiform orifice but may be displaced antero-laterad. Minute setae may be present around the sub-marginal, but they are very difficult to detect. Geminate pore/porettes are aligned in three or four longitudinal groups. The dorsum may be smooth, without papillae or projections other than setae, or have pronounced longitudinal mid-dorsal and sub-dorsal rows of tubercles. The vasiform orifice is triangular or occasionally quadrate, longitudinal sides concave, half covered by the operculum, open behind and inset from margin by approximately its own length; length 59 microns (52–68 microns). The lingula is spatulate with two pairs of enlarged setae, the distal portion is spiculate, and it is half-covered by the operculum. Operculum and lingula may be pigmented light brown.

Ve n t e r. Cuticle diaphanous and smooth. Derm of thoracic tracheal folds usually with numerous, minute spinules. Middle and hind coxae each with a fine, hair-like seta, and an adjacent minute spine-like seta. Antennae length 17 microns (14–20 microns).

ADULT ( Figs 10–14 )

Body yellow, wings hyaline, covered with sparse, powdery wax. Antennae 7-segmented. Antennal segment II about half as long as antennal segment III; antennal segment III about as long as segments IV–VII combined; segments V–VII subequal, segment IV shorter. Segment II with long, slender, conical sensorium (difficult to distinguish from the enlarged setae). Segment III with one sensorium located on the proximal portion, and three sensoria (a cone and two rhinarial-types) on the distal portion. The cone is approximately a quarter to a third the segment length away from the apex. Segment IV without a sensorium; segment V with an distal rhinarial-type sensorium; segment VI with a subapical sensorial cone, and segment VII with both a sensorial cone and an adjacent rhinarial sensorium, arising near the middle of the segment and the segment terminating in a narrow conical sensorium. Upper eye composed of about 40–47 ommatidia, each 8.8 (8.0–9.6) microns in diameter; lower compound eye composed of about 32 ommatidia, each 10.9 (9.8–12.3) microns in diameter, arranged in interconnected groups of 6 pigmented ommatidia surrounding a clear, smaller ommatidium. Upper and lower eyes connected by a single clear ommatidium. Metatibial combs consisting of 16–17 setae, all tibial brushes consisting of two or three adjacent setae. Male claspers paired, with about 10–11 long setae. Aedeagus ventral base smooth; distal portion straight, almost parallel sided with little or no curve upwards, blunt ended, sometimes terminating with a small fine tip. Male collar and female gonapophysis and supragenital plate unpigmented. Female cement gland is sinuous, without bands and with a small head.

Figures

FIGURES 5 – 9. Bemisia afer. 5, ovum on Laurus nobilis from Italy; 6, first instar on L. nobilis from Italy; 7, second instar on L. nobilis from Italy; 8, third instar on L. nobilis from Italy; 9, fourth instar on Manihot esculenta from Mauritius.

FIGURES 10 – 17. Bemisia spp. 10, B. afer, diagrammatic representation of left compound eye of adult female; B. afer, 11, upper and lower compound eyes linked by one ommatidium; B. afer, 12, female antenna; B. afer, 13, aedeagus; B. afer, 14, female cement gland; 15, B. tabaci, ovum on Euphorbia pulcherrima; 16, B. tabaci, first larval instar on Solidago from Spain; 17, B. tabaci, second instar on E. pulcherrima.