How to Manage Pests
UC Pest Management Guidelines
Scientific name: Leptoglossus clypealis and Leptoglossus occidentalis
(Reviewed 3/09, updated 11/12)
In this Guideline:
DESCRIPTION OF THE PEST
The leaffooted bug is an infrequent pest in almonds that gets its name from the small, leaflike enlargements found on the hind legs of the large nymphs and adults. Adult bugs are about 1 inch long and have a narrow brown body with a yellow or white zigzag line across its flattened back. Adult females lay eggs in strands of usually 10 to 15 eggs that are often found on the sides of nuts in almonds. Eggs hatch into small nymphs that resemble newly hatched assassin bugs.
Although it is an infrequent pest in almonds, in years when weather and other conditions are right, significant damage can occur, especially in the lower San Joaquin Valley. The leaffooted bug overwinters in the adult stage in aggregations in orchards, or near orchards on native host plants, from which it migrates into orchards in March or early April in search of nuts on which to feed. Feeding by adult leaffooted bugs on young nuts before the shell hardens can cause the embryo to wither and abort, or may cause the nut to gum internally, resulting in a bump or gumming on the shell. It can also cause nut drop. After the shell hardens, leaffooted bug feeding can still cause black spots on the kernel or wrinkled, misshapen nutmeats. Varieties with softer shells such as Fritz, Sonora, Aldrich, Livingston, Monterey, and Peerless are more susceptible to bug damage for a longer period during the season.
Be careful not to confuse leaffooted bug damage with damage by stink bugs. Both pests damage nuts by probing them with their needlelike mouthparts, and both result in gumming on the hull. In most cases, leaffooted bug damage occurs in March and April while stink bug damage is more common in May and June. Another way to distinguish damage, considering that symptoms are so similar, is to find the actual bugs or their egg masses.
Egg parasites, Gryon spp., often keep populations of leaffooted bug below economically damaging levels. However, as egg parasites, they have no ability to control the overwintering adult leaffooted bugs that migrate into orchards in spring.
Monitoring and Treatment Decisions
Walk the orchard during the months of March and April to look for dropped nutlets (particularly on susceptible varieties), nuts with gummosis, and leaffooted bugs. Finding adult bugs is the best indication that a problem may arise, but the cryptic nature of these pests and their behavior of staying in the tops of trees makes this difficult to do. A more practical approach is to look for nuts with gummosis or egg masses on the sides of nuts. If gummosis exists, cut a cross-section across the damaged site to look for a puncture mark from the bug's mouthparts to confirm that the gummosis is not due to physiological reasons.
The easiest monitoring method is to look for aborted nuts on the ground. However, basing treatments on gummosis and nut drop also means that there can be a 7-10 day lag time between when feeding takes place and when gummosis and nut drop occur - so the dispersing insects may have already moved to another block.
Treatment thresholds have not been developed for this pest in almonds, but low numbers of bugs can cause substantial damage. If bugs and their damage are evident, consider a treatment. Chemical control generally targets the overwintering adults that have migrated into the orchard with April or May applications. Unfortunately, the broad-spectrum products that are most effective against leaffooted bugs are also very disruptive to biological control agents of spider mites and other almond pests. Later applications are not needed when populations of overwintering adults and nymphs, with mouthparts that are too small to feed on the kernel, have declined.
UC IPM Pest Management Guidelines:
Insects and Mites
F. G. Zalom, Entomology, UC Davis