Sudan Gyawaly, UC IPM Advisor, Sacramento Valley

Carpophilus truncatus, commonly called the carpophilus beetle, is a tiny (~1/10 inch long) insect and a new threat to California nut crops. A key pest of almonds in Australia, this insect reportedly causes an average of 2-5% damage in Australian almonds. The beetle was first detected in multiple counties in the San Joaquin Valley almond and pistachio orchards in 2023; since then, it has been found in these nut crops in other regions across California, including the Sacramento Valley.

I have been conducting detection and monitoring surveys of this pest as part of statewide surveys, in collaboration with other UC entomologist colleagues, in multiple nut-crop orchards for the last couple of years. My recent surveys have confirmed that the beetle is also present in several orchards in the Sacramento Valley, though we have not seen widespread damage by this pest yet. In our surveys, the traps captured several thousand beetles (most of which were from one of multiple carpophilus species that don’t attack nuts in the tree), but a small number were C. truncatus beetles recovered from two almond and two pistachio orchards.

In addition to the trap survey, we also received multiple suspicious beetles and infested nut samples from PCAs and Consultants throughout the season. After diagnosis, we found several C. truncatus beetles and larvae in walnut samples recently collected from the orchard floor of a well-managed Chandler orchard in the region. A well-known pest of almonds in Australia, C. truncatus has been reported in walnuts in other countries, including Italy, Chile, and recently Australia, but the degree of infestation in walnuts seems lower than in almonds and pistachios. In the Central Valley, C. truncatus was first detected infesting a walnut block in Stanislaus County in 2023. The detection of this beetle in the walnut block in our region highlights the importance of paying attention to this pest in walnut orchards as well.

The carpophilus beetles overwinter as adults in remnant nuts, known as “mummy nuts,” predominantly in the ground. They seem to utilize those nuts for building populations until the hullsplit. Therefore, orchard sanitation, particularly shredding or destroying nuts on the ground, is a critical management practice for this pest. In studies conducted by UC researchers, insecticides have provided limited control of this pest so far. In summer, beetles lay eggs on hullsplit nuts, and larvae and adults feed directly on the kernel. This beetle’s damage can be confused with navel orangeworm damage, as both feed on the kernels and often infest the same nut, making it challenging to find tiny beetle larvae in a mix of frass and nutmeat powder. Navel orangeworm feeding produces brown frass with copious webbing, while carpophilus beetle produces fine powder frass with minimal webbing. Inspecting hull-split nuts during the season and/or mummy nuts during the winter is the best way to detect these beetles and damage. Additionally, a visual guide is available to identify carpophilus beetle damage; you can access it by clicking the link or googling “visual guide to identify carpophilus beetle damage”. We will continue to monitor this pest to track its status in the Sac Valley, and we encourage you to contact us if you need help identifying beetle damage or have seen any.