How to Manage Pests
UC Pest Management Guidelines
Caterpillars and their Natural Enemies
(Reviewed 1/07, updated 6/10)
In this Guideline:
Caterpillars are the larvae of moths and butterflies (order
Lepidoptera). Omnivorous looper, western
avocado leafroller (amorbia), and
(least frequently) orange tortrix are sporadic
pests in avocado. Healthy trees can tolerate some loss of chewed foliage and
blossoms. Extensive defoliation can result in sunburn to fruit and twigs.
Economic damage occurs primarily when caterpillars chew and scar fruit. Conserve
natural enemies, as caterpillars are usually under effective biological
IDENTIFYING CATERPILLARS AND NATURAL ENEMIES
SAMPLING CATERPILLARS AND THEIR NATURAL ENEMIES
- From March through August, monitor at least 10 trees per grove
about every 7 to 10 days, concentrating efforts in areas where you see leaf
chewing or found caterpillars the previous season.
- Sample caterpillars
using timed counts or foliage shaking, as described below, depending on the
- For all samples
combined from each tree, record the total number of caterpillars and the total
predators of caterpillars.
- Record separately any
apparently diseased and parasitized caterpillars, also record any diseased or
parasitized larvae in the caterpillars per hour or caterpillars per 25 shakes
column. (This "double counting"
prevents the caterpillar pressure calculation from being altered by variations in the ratio of predators to
diseased or parasitized
it is not obvious whether a caterpillar is healthy versus diseased or parasitized, or if you don't know if
the observed species are predators
of caterpillars, collect those specimens for closer examination
later. This is especially
important when conducting timed counts, so time is not diverted from inspecting
trees during the fixed monitoring time.
Using the Shake Method
Shake foliage to sample avocado
- Place a 1-yard square
collecting surface (e.g., cloth or flattened cardboard box) beneath outer canopy foliage.
- Vigorously shake small limbs
to dislodge caterpillars onto the collecting surface. (For example, shake foliage on 2 or 3 separate
sections of each tree to collect 25 shake samples.)
Using the Timed Method
Make timed counts for amorbia (western avocado leafroller), avocado looper, and orange
- Spend a fixed amount of time
inspecting foliage for caterpillars.
For example, spend 6 minutes inspecting each of 10 trees (1 hour).
- Use an alarm watch or timer
to ensure the entire period is
spent monitoring, and that time spent moving among distant trees is not included.
- Walk slowly around the outer
canopy, looking for chewed and webbed
foliage or fruit. Pull apart webbing and count any caterpillars and natural enemies.
- Record results on a caterpillar
and biological control sampling form .
MONITORING ADULT MOTHS
Adult moths are nocturnal and consume only liquids and pollen.
During the day they rest on the underside of leaves or on shady bark.
- Deploy pheromone-baited sticky traps for
adults to identify the species in groves and indicate peaks in flights of
egg-laying adults. Each trap is baited with a separate pheromone to attractU
adult male amorbia, omnivorous looper, or orange tortrix. For amorbia, two
different pheromones are used, one for northern California and the San Joaquin
Valley and another for southern California including Ventura County. Unless
other methods are recommended, deploy traps at a density of about one trap per
ten acres when adult moths are expected to be present. Check with suppliers for
recommended pheromones and the type and number of traps to use.
- Trapping moths can indicate that foliage
monitoring is warranted and helps to time management actions such as release of
parasites. Adult traps generally are not useful for determining need for
treatment, partly because caterpillars are the damaging stage and natural
enemies kill many eggs and larvae relative to the moth population that is
trapped earlier in the season.
UC IPM Pest Management Guidelines:
UC ANR Publication
Acknowledgment for contributions to General Horticultural Information:
M. L. Arpaia, Botany and Plant Sciences, UC Riverside
M. L. Bianchi, UC Cooperative Extension, San Luis Obispo County
C. J. Lovatt, Botany and Plant Sciences, UC Riverside
P. Mauk, UC Cooperative Extension, Riverside County
G. W. Witney, California Avocado Commission, Irvine, CA
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