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AVOCADO LEAF GALLING PSYLLID Trioza anceps Tuthill, Trioza perseae Tuthill,
Trioza aguacatae Hollis and Martin, Trioza godoyae Hollis and Martin Hemiptera, Psylloidae ----- CLICK on Photo to enlarge
& search for Subject Matter with Ctrl/F. GO TO ALL: Bio-Control Cases Four species of Trioza are
currently known to attack avocado foliage and nymphal feeding causes some
form of leaf deformation. Trioza anceps Tuthill
is associated with avocados throughout Mexico and Central America. Trioza
perseae Tuthill has been described from avocados growing
in Peru, and Trioza aguacatae Hollis
and Martin and Trioza godoyae Hollis
and Martin are known from avocados in Michoacan Mexico, and San Jose Costa
Rica, respectively (Hollis and Martin 1997).
All four Trioza spp.
appear to have an extremely restricted host range and have only been recorded
from leaves of avocados (Persea americana).
Further, under some circumstances certain Trioza species
(e.g., T. perseae) may even be restricted to particular
races of P. americana, which is
suggestive of extreme monophagy and host specialization (Hollis and Martin,
1997). Trioza species have been
found on smuggled avocado plants intercepted in San Antonio and Brownsville
in Texas, and San Diego in California (Texas and California are states in the
USA) (Hollis and Martin 1997). Currently, none of the four Trioza species
known to attack avocado leaves are present in the major avocado growing
states of the USA (i.e., California, Florida, Texas, and Hawaii).
However, given the relatively close proximity of Mexico to California ,
the high daily volume of tourism, traffic (road, rail, sea, and air), and trade
across the California-Mexico border, and the potential for illegal movement
of plant material through these identifiable conduits, Trioza
anceps and T. aguacatae have
high invasion and establishment potential should they be illegally moved on
avocado plants that are introduced into California. Consequently, Trioza species
represent a serious biosecurity risk for California (the largest avocado
producing region in the USA at ~65,000 acres), and other minor avocado
producing areas in the USA (especially Texas and Florida). Around 58 species of psyllids (~2% of
described species) are associated with host plants in the Lauraceae, the
plant family to which avocados belong. The majority of these psyllid species,
~72% of them, belong to the family Triozidae which contains the genus Trioza,
of which ~64% cause some type of leaf deformation to their lauraceous hosts
(Hollis and Martin 1997). Adult Trioza. Trioza species
adults are small (~3mm in length), winged, and depending on the species, coloration
is either pale green or brown with ochraceous markings. Forewings are hyaline
with pronounced veination that may be useful for species identifications.
Adults have been observed feeding on avocado leaves, presumably imbibing
phloem. Female Trioza species
probably oviposit eggs into young avocado leaves by partially inserting them
into leaf tissue with the ovipositor. Virtually nothing is known about
the basic developmental and reproductive biology and ecology of Trioza species
associated with avocados and these are important areas of research in need of
attention. Trioza nymphs. Nymphs are
the life stage responsible for causing characteristic deformaties to avocado
leaves. Trioza species
normally have five nymphal instars before molting to the adult stage.
Female T. anceps, T. aguacatae,
and T. godoyae apparently lay eggs on the underside
of young tender avocado leaves. Nymphs of T. anceps and T.
aguacatae upon emerging from eggs create a
"pit" within which they commence feeding. As nymphs mature, they
induce the formation of protective galls within which they feed. Galls are
typically conical vertical growths of leaf material that form on the leaf
surface opposite to which the feeding pit is initiated. Typically this is the
upper leaf surface for T. anceps and T.
aguacatae. T. perseae nymphs
apparently feed in pits on the upper leaf surface which then causes gall
formation on the lower surface of the leaf (Hollis and Martin 1997). T.
godoyae nymphs do not form projecting galls, instead nymphs
of this species cause the edges of leaves to roll and feeding occurs within
these protective structures (Hollis and Martin 1997). Very little, if anything, is known
about the physiology of gall induction by Trioza species
associated with avocados, how nutrition is acquired from within galls,
factors influencing development (e.g., temperature, avocado race, leaf age,
exposure of leaves to sun and shade, and densities of nymphs and galls per
leaf). Feeding Damage Nymphal Trioza species
induce galls that either develop on the upper or lower leaf surface, or they
cause leaf margins to roll. The type of leaf damage observed on avocados is
dependent on the species of Trioza infesting the
plant. Trioza anceps and T. aguacate cause
galls to develop on the upper leaf surface, T. perseae induces
gall formation on the lower leaf surface, while T. godoyae infestations
result in leaf margins curling. Attacks by Trioza
magnoliae on redbay (Persea borbonia)
appear to more intense when plants are shaded, and galled leaves tend to be
smaller, senesce more rapidly, and shoots with galled leaves grow less in
comparison to shoots lacking galled leaves (Leege 2006). These field
observations of T. magnoliae on P.
borbonia suggest that gall induction negatively affects
plant growth and reproduction (Leege 2006). Consequently, it is possible
that Trioza species attacking avocados have similar
negative impacts on this host plant. Therefore, it is not surprising
that reports from Mexico indicate that heavy Trioza sp.
infestations can cause premature leaf defoliation which reduces avocado fruit
production (Ebeling 1950, Hernandez et al., 2000). Biological Control There are no readily available
published records on the natural enemy fauna associated with Trioza species
that induce galls in avocados. It is likely that there are specialist
hymenopterous parasitoids attacking Trioza nymphs
within galls that await discovery in countries with endemic Trioza species.
Discovery, identification, and study of these parasitoids, should they exist,
could be very important for developing IPM programs in areas with
naturally-occurring Trioza species.
Knowledge of these natural enemies could be invaluable for future biological
control programs against invasive Trioza species
in countries with avocado industries that currently lack this pest.
Adult Trioza are probably
opportunistically preyed upon by generalist natural enemies (e.g., lace wing
larvae, spiders, and coccinellids) on avocados. Many species of psyllids are known to
have parasitoids (e.g., Hymenoptera: Eulophidae) that attack nymphs. Some
species of invasive psyllid attacking agriculturally important crops has been
subjected to classical biological control (e.g., Asian citrus psyllid, Diaphorina
citri in Florida with Tamarixia radiata (Waterston)
[Hymenoptera: Eulophidae]). Invasive pest psyllids attacking landscape
ornamentals have been controlled with specialist natural enemies also (e.g.,
Eugnenia psyllid, Trioza eugeniae, has been
suppressed in parts of California with Tamarixia sp.). REFERENCES: [Additional references may be found at: MELVYL Library ] Ebeling, W. 1950.
Subtropical Entomology.
Lithotype Process Co., San Francisco, USA. Hernandez, H. G., R.
Johansen Naime, L. Gasca Corona, A. Equihua Martinez, A. Salinas Castro, E.
Estrada Venegas, F. Duran de Anda, & A. R. Valle de Paz. 2000.
Plagas del Aguacate. In:
"El Aguacate y Su Manejo Integrado" Ed. D. Teliz, pp. 117-136.
Ediciones Mundi-Prensa, Mexico D.F. Hollis, D. & J.
H. Martin. 1997. Jumping plantlice (Hemiptera: Psylloidae)
attacking avocado pear trees, Persea americana, in the New
World, with a review of Lauraceae-feeding among psylloids. Bulletin of Entomological Research 87:
471-480. Leege, L. A. 2006. The
relationship between psyllid leaf galls and redbay (Persea borbonia)
fitness traits in sun and shade. Plant Ecology 184: 203-212. |
