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BIOLOGICAL
CONTROL OF THE NAVEL ORANGEWORM Amyelois transitella
(Walker) Phycitidae Two external
larval parasitoids, Goniozus legneri
Gordh and Goniozus emigratus (Rohwer) and one internal
egg-larval parasitoid, Copidosomopsis
plethorica Caltagirone,
which are dominant on navel orangeworm in south Texas, Mexico, Uruguay and
Argentina, were successfully established in irrigated and nonirrigated almond
orchard in California\'s Central Valley in 1979-86 (Caltagirone 1966, 1964;
Legner & Silveira-Guido 1983). Separate k-value analyses indicated
significant regulation of their navel orangeworm host during the warm summer
season. Variable percentages of field-collected larvae of the navel
orangeworm and the imported parasitoids have required significantly longer
developmental periods to the adult stage than those in laboratory control
cultures. These differences indicate diapause in the host triggered by
several seasonally varying factors, and a diapause in the parasitoids
triggered by hormonal changes in the host. Possible latitudinal effects on
diapause are also observed. The ability of the imported parasitoids to
diapause with their host enables their permanent establishment and ability to
reduce host population densities to economic levels (Legner 1983). CLICK on Photo for greater detail The
relationship between residual almond mummies on densities of the navel
orangeworm and parasitism has been demonstrated (Legner 1983a). The two
imported Goniozus
parasitoids have also been shown capable of regulating navel orangeworm at
low densities (Legner & Silveira-Guido 1983, Legner & Gordh 1992).
Superimposed upon the whole system is a diapausing mechanism in both the
navel orangeworm and the parasitoids (Legner 1983b). Efforts are now required
that would tie together all these forces into a sound, reliable integrated
management, which would allow growers to make reasonable decisions on whether
or not to remove mummied almonds, or to use within season sprays. Populations
of navel orangeworm have been followed since 1979 in six almond orchards near
Paso Robles, Hilmar, Chowchilla, Selma, Westley and Atwater, to determine the
impact of the parasitoids. A clear drop in the average density of navel
orangeworm in all orchards is coincident with the establishment of the three
parasitoids (Legner & Gordh 1992). However, the almond reject levels are
not always below the economic threshold of in all orchards. Careful
investigations show that invariably such rejects are due to other causes,
such as ant damage and fungus infections. In certain years the peach twig
borer has been found to be the principal cause, which subsequently stimulates
oviposition by navel orangeworm moths. Packing plant appraisals frequently
attribute damage incited by twig borer to the navel orangeworm.
Copidosomopsis plethoricus
and Goniozus legneri, and to a
lesser extent Goniozus
emigratus overwinter
in release orchards year after year. However, only Copidosomopsis can consistently be recovered
at all times of the year. The Goniozus
species are not recovered in significant numbers until early summer. However,
adults of the latter are frequently observed in large numbers during autumn
and early spring months.
Goniozus legneri has been reared from codling moth and oriental fruit moth in peaches in
the Paso Robles area in addition to navel orangeworm from almonds. Field data
suggest that a certain number of old mummied nuts is necessary to maintain a
desirable synchrony of these parasitoids with navel orangeworm to produce the
lowest average densities (below 4% damage at harvest). In fact, at Paso
Robles mummies often exceed 1,000 per tree through the winter months, and
produce navel orangeworm densities at harvest at below 1% on soft-shelled
varieties. Pest
management in almond orchards frequently involves periodic releases of
Goniozus legneri and/or Copidosomopsis plethoricus to reestablish balances
that were disrupted by insecticidal drift or by the absence of overwintering
mummied fruit refuges. Goniozus legneri
(Discovery & Habits)
--The discovery of Goniozus legneri in South America
involved making initial contact with Dr. José Pastrana of the University of
Buenos Aires. Arrangements were made for Dr. Legner to meet with Dr. Pastrana
in Punta del Este, Uruguay in 1977. The navel orangeworm was not a common
insect at higher latitudes in South America, and Dr. Pastrana only recalled
having studied it in his collections from central Argentina. He advised Dr.
Legner to travel to Concordia, Argentina to inquire there. In
Concordia, Legner was accompanied by Dr. Aquiles Silveira-Guido, where both
of them searched through collections in the experiment station there. A dusty
room, filled to the ceiling with wooden insect collection boxes, was searched
intensively. Several specimens of the navel orangeworm were found from
collections made in 1938, and from the host coral tree, Erythrinia crista-galli. This knowledge
enabled a further search in the wild on this host tree.
Subsequently, collections were continued in Argentina and Uruguay with the
aid of Dr. Silveira-Guido. Goniozus
legneri turned out to be the most frequently collected parasitoid
from navel orangeworm and the imported carob moth, Ectomyelois ceratoniae (Zeller), with other parasitoid
species of only ca. 5% occurrence being Temelucha
sp, Coccygonimus sp. and
Venturia canescens (Graven-Stein), Bracon sp. & Copidosoma sp. Cultures sent to
Riverside, California were attempted, but only G. legneri succeeded. Collections
were also made from Texas where it was found that Pentalitomastix (Copidosoma) plethorica parasitized navel
orangeworm on Nonpareil almonds as far north as Brownwood (33 deg. N. lat.)
and on Texas ebony and western soapberry seeds along the Gulf of Mexico coast
and throughout south Texas. At the latitude of Corpus Christi, another parasitoid,
a biparental strain of Goniozus emigratus
was found attacking this host at low densities in all seasons on western
soapberry and Texas ebony. Although identified as G. emigratus by Gordh & Hawkins (1981), its biparental
behavior and fecundity differed significantly from the uniparental Hawaiian
form to indicate its possible sibling status. REFERENCES: Caltagirone, L.
E. 1966. A new Pentalitomastix from Mexico. The Pan
Pacific Entomol. 42: 145-151. Caltagirone, L. E., K. P. Shea and G. L. Finney.
1964. Parasites to aid control of navel orangeworm. Calif. Agric. 19(1):
10-12. Gordh, G. 1982. A new species of Goniozus imported into California for
the biological control of navel orangeworm[Hymenoptera: Bethylidae;
Lepidoptera: Pyralidae]. Entomol. News 93: 136-138. Gordh, G. & B. Hawkins. 1981. Goniozus emigratus (Rohwer), a primary external parasite of Paramyelois transitella (Walker), and comments on bethylids attacking
Lepidoptera [Hymenoptera: Bethylidae; Lepidoptera: Pyralidae]. J. Kansas Entomol.
Soc. 54: 787-803. Gothilf, S. 1978. Establishment of the imported
parasite Pentalitomastix plethoricus [Hym: Encyrtidae] on Ectomyelois ceratoniae [Lep: Phycitidae] in Israel. Entomophaga 23:
299-302. Legner, E. F.
1983a. Influence of
residual Nonpareil almond mummies on densities of the navel orangeworm and
parasitization. J. Econ. Entomol. 76: 473-475. Legner, E. F. 1983b.
Patterns of field
diapause in the navel orangeworm (Lepidoptera: Phycitidae) and three imported
parasites. Ann. Entomol. Soc. Amer. 76: 503-506. Legner, E. F. & G. Gordh. 1992. Lower navel
orangeworm (Lepidoptera: Phycitidae) population densities following
establishment of Goniozus legneri (Hymenoptera: Bethylidae) in
California. J. Econ. Ent. 85(6): 2153-60. Legner, E. F.
& A. Silveira-Guido. 1983. Establishment of Goniozus
emigratus and Goniozus legneri [Hym: Bethylidae] on navel orangeworm, Amyelois transitella [Lep: Phycitidae] in
California and biological control potential. Entomophaga 28:
97-106. Legner, E. F., G.
Gordh, A. Silveira-Guido & M. E. Badgley. 1982. New larvicidal wasp to attempt control of
navel orangeworm. Almond Facts 47(3): 56-58. Legner,
E. F., G. Gordh, A. Silveira-Guido & M. E. Badgley. 1982. New wasp may
help control navel orangeworm. Calif. Agric. 38(5-6): 1, 3-5. |