Western Colorado Insects
Pests Affecting Native Plant Seed Production
Great Basin Native PlantsUncomphagre Plateau Project
Penstemon angustifoliaPenstemon strictus

Penstemons

Scientific Name: Scrophulariaceae: Penstemon sp.

Common Name:
Penstemon - many species

Plant Abbreviation:
PE**; P. palmeri - PEPA; P. strictus - PEST; P. barbatus - PEBA

Description:
Penstemons are some of our showiest wildflowers. Many species of Penstemon are grown for seed in western North America. They are used for reclamation, restoration, and landscape purposes. Seed production has been relatively pest free, but borers and Lygus have caused significant local problems.


The Penstemon Weevil

Scientific Name: Coleoptera: Curculionidae: Hesperobarus ovulum ??

The Penstemon weevil is know only from SW CO, where it has caused catastrophic damage to several species of Penstemon seed production fields - PEPA, PEST, PEBA. It attacked 2 and 3 year old fields and resulted in stand decline severe enough to justify field removal.

The taxonomy of this insect is uncertain and a weevil taxonomist is currently working on identification.

Penstemon Weevil AdultAdult

Adult weevils are rarely seen because of their nocturnal habits. They are active in the fall and spring. They are dark brown, and slightly more than 3 mm in length. They have a heavy, slightly curved snout.

Eggs

Eggs are not described, but they are probably laid in the spring in the crown area of the plant.

Penstemon Weevil LarvaeLarvae

The larvae are grub like, with a distinct head capsule and no legs. They are found inside the stems on the lower part of the stem or at crown level.

Pupa

Pupation is within the cell made by the larvae. Pupae are present in mid to late summer in SW CO. Pupae have not been photographed yet.


Management

Penstemon weevils are known only from SW Colorado and may not be a pest elsewhere. If you suspect you have seen them, please contact Bob Hammon.

Penstemon weevil management is difficult because once damage is observed, no controls are available. There are no good monitoring techniques developed for the insect yet. Adult weevils are nocturnal, making sweep sampling ineffective. Suction sampling has not been tried yet, but may be an effective monitoring method.

It is important to monitor native Penstemon within a few miles of a seed production field for the presence of weevils. If they are present, keep an eye out for their presence in fields once they are 1 year old.

Two types of preventative controls are possible:

1) Foliar applications of a contact residual insecticide such as a pyrethroid, aimed at adult weevils, can prevent egg deposition. These sprays should go on in late fall and/or early spring.

2) A systemic neonicitinoid insecticide applied to the soil in young fields could prevent damage. There has been no research to evaluate this method yet.


Photo Gallery

Weevil Damage in Penstemon

 

This picture shows weevil feeding damage in the taproot of a PEPA plant.

 

 


This page was updated on April 26, 2014