I have been several calls in regards to leaffooted plant bug (Leptoglossus clypealis and L. occidentalis). Damage has been reported from various areas of the county, with significant damage observed within some blocks.
Leaffoted plant bugs get their name from the leaflike features found on the back legs of the large nymphs and adults. Adults are about 1 inch long and have a yellow or white zigzag line across their back. Females lay eggs in strands which are often found on the sides of almonds or pistachios.
Prior to shell hardening, leaffooted plant bug feeding will cause nut drop by killing the embryo. Feeding may also cause the nut to gum internally, resulting in gumming on the shell. After the shell hardens, leaffooted bug feeding can still cause black spots on the kernel or wrinkled, misshapen nutmeats. Damage from leaffooted plant bug feeding from various times of the year can be seen here. Fritz, Sonora, Aldrich, and Monterey appear to be more susceptible to bug damage for a longer period during the season.
Treatment thresholds have not been developed for this pest in almonds, but low numbers of bugs can cause substantial damage. Treatment should be considered if bugs are found and if damage has occurred, especially if early in the growing season (April – May). Basing treatments off of observation of symptoms, however, usually means a 7-10 day lag time between when feeding takes place and when nut drop occurs. Research is needed to determine a predictive tool for preventative leaffooted plant bug treatments. Although anecdotal, leaffooted plant bug damage seems to be worse within Merced County in years of low winter rainfall. Perhaps migrating populations move earlier into the almond crop, which causes increase crop loss.
Control treatments consist of using broad spectrum insecticides (pyrethroids, neonicotinoids, and organophosphates) and target the overwintering adults that have migrated into the orchard in April or May. These treatments will often disrupt biological control agents of spider mites, and the inclusion of a miticide should be considered. Since the treatments are made after the damage has occurred it is unknown how effective these sprays are in controlling the insects. After June, damage usually decreases due to decreased population of adults, and the inability of nymphs to penetrate the hull due to mouthparts that are too small to feed on the kernel.
More information can be found at the UC IPM Website.