How to Manage Pests
UC Pest Management Guidelines
Leaffooted Plant Bugs
Scientific names: Leptoglossus zonatus, Leptoglossus clypealis, Leptoglossus occidentalis
(Reviewed 10/14, updated 10/14)
In this Guideline:
DESCRIPTION OF THE PESTS
Adult leaffooted plant bugs are relatively large insects, 3/4 to 1 inch in length. All three species are similar in appearance; they are brown in color with a narrow white band across the back, although this band is less distinct in L. occidentalis. The head appears pointed, and the hind legs have an expanded area that superficially resembles a leaf, hence its name. Leptoglossus zonatus can be distinguished by the presence of two yellow spots on the pronotum. Leptoglossus clypealis does not have the yellow spots and has a long pointed clypeus that points forward at the front of the head.
Leaffooted bugs overwinter as adults, typically in aggregations located in protected areas, such as in woodpiles, barns, under the bark of eucalyptus, citrus, palm, cypress, or juniper trees. These pests can also overwinter in the orchard in plant debris, pump houses, or cracks along the tree trunk. From late March through May, adults disperse to find food sources. These insects are primarily seed feeders and, once in the orchard, they will feed directly on the developing nuts or on ground vegetation. Adults are strong flyers and can disperse from overwintering sites and quickly move into and within the orchard. Overwintered adults are long-lived, from September or October to April or May. Their eggs are laid in spring usually on leaves, twigs, and nuts; some Leptoglossus species deposit over 200 eggs. After nymphs emerge from a round hole on top of the egg, they develop into adults in 6 to 8 weeks. Because the adults are long-lived and can lay eggs over an extended period, the population can consist of all life stages by late June. There may be 2 to 3 generations per year, depending on temperatures and food sources.
These insects are capable of causing two types of damage. The first type (epicarp lesion) is produced early in the season and is similar to that caused by other plant bugs. Nuts damaged during or shortly after bloom blacken and drop. If nuts are damaged during the period in which they are enlarging, the damaged tissue turns brown and necrotic and the outside will often become sunken and appear almost water soaked. The internal lesions often develop a white, netted appearance in the shell tissue, with no deep pitting.
After shell hardening in June, leaffooted bugs may cause a second type of damage called kernel necrosis, which is not obvious on the shell. Externally all that is evident is a brown pinpoint mark. With kernel necrosis, the nutmeat is darkened, often develops a sunken or distorted area, and may have an off-flavor. If this occurs when humidity is high, a fungal breakdown of the nut causes it to turn slimy. This is referred to as stigmatomycosis.
Leaffooted plant bugs typically damage most of the nuts in an attacked cluster.
Leaffooted bugs typically first appear in orchards starting in April. However, if they overwinter in or near pistachio, they may be found earlier, usually feeding on nut clusters, and at this time they can cause considerable nut drop when their populations densities are high.
In most years leaffooted bug populations are controlled by natural mortality from extremely cold winter temperatures and an egg parasitoid (Gryon pennsylvanicum). However, these natural controls cannot be relied upon if there is a large overwintering population typically following a mild, dry winter. This is especially true during the critical spring period as the egg parasitoid will only impact the adult's offspring, and it is the overwintered adult that will cause most damage.
During the season there are no cultural controls known to affect the density of the leaffooted bug or the damage it causes to pistachios. However, cultural controls such as cleaning debris from near the orchard may help reduce overwintering populations.
Monitoring and Treatment Decisions
During dormant and delayed dormant tree pruning, check for leaffooted plant bug when looking for Botryosphaeria cankers.
Starting in April monitor weekly through nut development.
UC IPM Pest Management Guidelines: Pistachio
Insects and Mites
D. R. Haviland, UC Cooperative Extension, Kern County