Stylet penetration by the bayberry whitefly, as affected by leaf age in lemon, Citrus limon

Abstract

Bayberry whitefly (Parabemisia myricae [Kuwana]) crawlers were placed on young and mature lemon leaves and were allowed 7–9 days to settle. Afterwards, the nymphs were fixed and sectioned in situ on the leaves and the area of leaf under each whitefly was examined at 1 000 × for stylet penetration. Both stylets and stylet tracks were readily visible in the sections. The path of penetration was mostly intercellular and the objective appeared to be the phloem. Passage of the stylets through the plant tissue did not cause detectable damage to most cells; however, damaged plant cells occasionally were noticed. Nymphs that had moulted during the 7–9 day settling period reached the phloem significantly more often than those that were still in their first instar. In each of the three replicates, penetration in the mature leaf occurred significantly less often than penetration in the young leaf (4% vs. 72%, p < 0.01, χ2). Penetration appears to be inhibited in the mature leaf either by the leaf cuticle or by factors detected by the nymphs after very shallow penetration into the leaf. The cuticle of mature leaves was much thicker than the cuticle of young leaves and may have been a barrier to stylet penetration. RÉSUMÉ Influence de l'âge des feuilles du citronnier (Citrus limon) sur la pénétration des stylets de l'aleurode, Parabemisia myricae Des larves de premier stade (avant la fixation) de l'aleurode, Parabemisia myricae (Kuwana), ont été placées, pour qu'elles se fixent, pendánt 2 à 9 jours, sur des feuilles jeunes ou mûres de citronnier. Des morceaux de feuilles avec des larves fixées ont été trempés dans 2% d'agar; ce procédé a permis de maintenir les larves à leurs sites de fixation finale. Des pièces d'agar contenant les morceaux de feuilles avec les larves ont ensuite été trempées dans de la paraffine, et sectionnées en séries de 10 μ. Il était nécessaire de maintenir une basse température pendant l'opération afin d'obtenir de bonnes sections des feuilles mûres durcies. Les stylets et leurs traces étaient faciles à voir dans les sections teintées aux safranins, et ‘fast green’. Presque toutes les traces des stylets étaient intercellulaires et leur destination semblaient être de phloème. En général, la plupart des cellules ne semblaient pas endommagées, les larves qui avaient mué pendant la période de 7 à 9 jours de fixation avaient atteint significativement plus le phloeme que les larves du premier stade. Dans trois essais, la pénétration des feuilles mûres était significativement moins fréquente que celle des feuilles jeunes (p < 0.01, χ2). La pénétration dans des feuilles mûres semble être empêchée par la cuticule ou par des facteurs perçus par les nymphes après une pénétration superficielle. La cuticule des feuilles mûres était beaucoup plus épaisse que la cuticule des jeunes feuilles et pourrait donc représenter une barrière à la pénétration des stylets.

Gall induction by hemipteroid insects

“…Walker (1987) determined that adults of Parabemisia myricae (Aleyrodidae) discriminate between young and mature lemon leaves from leaf-surface cues picked up by the sensilla on the rostral tip. Probing by first-instar nymphs could be limited by physical and/or chemical factors in leaf cuticle (Walker 1985). For instance, sucrose, in high likelihood, is a phagostimulant for inducing the settling response (Walker and Bednar 1986).…”

Life History, Functional Anatomy, Feeding and Mating Behavior

“…4.20a, c). Salivary sheaths remain in the plant after the stylets are withdrawn and are easily stained, providing a convenient record of everywhere that the whitefly probed with its stylets (McLean and Kinsey 1967;Walker 1985;Backus et al 1988;Cohen et al 1996b, c).…”

“…The stylet bundle of whiteflies is quite flexible and weaves its way between and around cells on its route to the phloem (Pollard 1955;Walker 1985;Walker and Perring 1994, Fig. 4.18).…”

Leaf age preference for opposition by three species of whitefly on lemon

“…Whitefly crawlers not only are poorly able to disperse to another plant, but they even are limited severely in their ability to disperse from the particular leaf where they were deposited as eggs (Lloyd, 1922;Dowell et al, 1978). Since leafage can be a critical factor affecting immature survivorship or development, as shown for the whitefly Parabemisia myricae (Kuwana) (Walker & Aitken, 1985;Walker, 1985), then leaf age discrimination by an ovipositing female may have a profound effect on her fitness.…”