Assessing Feeding Damage from Two Leaffooted Bugs, Leptoglossus clypealis Heidemann and Leptoglossus zonatus (Dallas) (Hemiptera: Coreidae), on Four Almond Varieties

Abstract

Leaffooted bugs (Leptoglossus spp; Hemiptera: Coreidae) are phytophagous insects native to the Western Hemisphere. In California, Leptoglossus clypealis and Leptoglossus zonatus are occasional pests on almonds. Early season feeding by L. clypealis and L. zonatus leads to almond drop, while late season feeding results in strikes on kernels, kernel necrosis, and shriveled kernels. A field cage study was conducted to assess feeding damage associated with L. clypealis and L. zonatus on four almond varieties, Nonpareil, Fritz, Monterey, and Carmel. The objectives were to determine whether leaffooted bugs caused significant almond drop, to pinpoint when the almond was vulnerable, and to determine the final damage at harvest. Branches with ~20 almonds were caged and used to compare almond drop and final damage in four treatments: (1) control branches, (2) mechanically punctured almonds, (3) adult Leptoglossus clypealis, and (4) adult Leptoglossus zonatus. Replicates were set up for eight weeks during two seasons. Early season feeding resulted in higher almond drop than late season, and L. zonatus resulted in greater drop than L. clypealis. The almond hull width of the four varieties in the study did not influence susceptibility to feeding damage. The final damage assessment at harvest found significant levels of kernel strikes, kernel necrosis, and shriveled almonds in bug feeding cages, with higher levels attributed to L. zonatus than L. clypealis. Further research is warranted to develop an Integrated Pest Management program with reduced risk controls for L. zonatus.

Augmentative biological control for squash bug (Hemiptera: Coreidae) using the egg parasitoid, Hadronotus pennsylvanicus (Hymenoptera: Scelionidae)

“…For instance, H. pennsylvanicus is currently being evaluated as a classical biological control agent for the invasive western conifer seed bug ( L. occidentalis ) in Europe (Roversi et al 2013, Lesieur et al 2018). In California, prospects are growing for H. pennsylvanicus as an augmentative biological control agent targeting the western leaffooted bug, Leptoglossus zonatus (Dallas), in almond and pistachio orchards as acreage expands and management issues with the pest intensify (Joyce et al 2019, Straser et al 2022). Researchers considering the releases of H. pennsylvanicus to manage these coreid species will benefit from and be emboldened by the knowledge gained from our rearing and deployment procedures used in this study.…”

Leaffooted Bugs: Insect Pest Species of Growing Concern for Agriculture

“…15 In California, L. zonatus has emerged as a significant pest in pistachio, almond, and pomegranate orchards, with feeding damage causing premature fruit drop and kernel necrosis in these crops. 7 In 2022, U.S. production of pistachio, almond, and pomegranate was valued collectively at greater than $6 billion. 16 Furthermore, L. zonatus decreases yield in maize, damaging the developing kernels (up to 15% yield loss) and reducing germination in maize grown for seed (U.S. production valued at greater than $91 billion in 2022).…”

“…2−5 As true bugs (Hemiptera: Heteroptera), Leptoglossus possess piercing-sucking mouthparts and engage in extra-oral digestion, injecting proteinaceous saliva 6 into developing seeds, fruit, and vegetative tissues of host plant species. Feeding damage caused by Leptoglossus species is similar to that caused by stink bugs (Heteroptera: Pentatomidae) and includes damage to developing seeds and premature fruit drop, 7 discoloration and necrosis, 8 and the transmission of plant pathogens. 9 Literature relating to Leptoglossus has grown steadily since the mid-20th century (Figure 1A) as species are identified as emerging agricultural pests, 10 invasive species, 11 or are named research area priorities by industry stakeholders.…”

Distribution of Two Strains of Leptoglossus zonatus (Dallas) (Hemiptera: Coreidae) in the Western Hemisphere: Is L. zonatus a Potential Invasive Species in California?

“…This species is recorded from dozens of host plant species including many which are economically important such as maize, citrus, tomato, cotton, pistachio and almonds [3][4][5][6][7][8][9][10][11]. In the last decade, L. zonatus has increased in abundance in California on almonds [12,13]. The apparent increase of L. zonatus could be attributed to factors including the increase in almond acreage in California [14,15], a changing climate which alters insect development and reproduction [16], or through the introduction of cryptic species or strains which are morphologically similar yet vary in their biological attributes [17].…”