The impacts of invasive invertebrates on plants are primarily studied on cultivated crops, with the effects on wild and threatened species mostly overlooked. The genus Phlomoides (Lamiaceae; common names include Jerusalem sage and Lampwick plant) comprises 174 species primarily occurring in Asia and some parts of Europe. The golden Himalayan spike Phlomoides superba (syn. Eremostachys superba) is an Endangered species (Srivastava et al., 2017, Journal of Threatened Taxa, 9, 10089–10095) endemic to the western Himalayan foothills of eastern Afghanistan, Pakistan and India, at altitudes of 450–800 m. There are concerns regarding its decline in natural habitats in several locations. The reasons are still poorly understood but low regeneration potential is one possible cause. In 2020, the species disappeared from its type locality in Mohand Pass, Dehradun, India.

In May 2023, we discovered that the major cause of the decline of P. superba appears to be infestation by an insect pest whose larvae feed on its seeds, leading to seed loss and thus affecting regeneration. In April 2024, we collected 20 larvae from three populations of P. superba in Jammu, India, and from plants growing in the garden of the Botanical Survey of India, Dehradun. We kept the larvae in transparent glass bottles for 25–32 days until pupation and emergence of the adult, which was then identified as the cotton bollworm Helicoverpa armigera (Lepidoptera: Noctuidae), a polyphagous, invasive moth globally recognized as a pest of c. 200 crops. From 1st to 3rd instar stage the larvae mainly feed on the tender leaves and then migrate to the seed capsules; we observed 90–95% seed loss in highly infested populations. Major infestations were found on P. superba near crop fields or human settlements. In ex situ conservation conditions, P. superba is growing well and regenerating at the Botanical Survey of India, Dehradun, where regular pesticide treatment controls the infestation, resulting in 95% seed survival and 84% seed germination.

The shift of crop pests to wild, threatened species needs to be monitored as many native and endemic species do not have natural defences against attacks by invasive pests. This discovery of the impact of H. armigera on a threatened wild plant species will be of help in development of a conservation protocol to address the ongoing decline of P. superba.

Helicoverpa armigera infestation on Phlomoides superba: (a–d) 3rd–6th instar larval stage feeding on seed capsules, (e) final instar and emptied seed capsules, (f) female adult moth. Photos: Amber Srivstava.