Short-spined Thrips: A New Pest Alert

Description

Short-spined thrips are very small and difficult to identify correctly without magnification or trained eyes. They exhibit sexual dimorphism, meaning males and females are different in appearance (Figs. 1 and 3). Fully developed females are typically about 1 to 1.2 millimeters long. To the naked eye, females look distinctly two-toned, with a top half that is light brown (head and thorax) and a much darker bottom half (abdomen), making them easier to distinguish from other thrips (Fig. 1). With proper magnification (Fig. 3), it is possible to see that they have seven-segmented antennae with the third segment distinctly lighter in color than any other segment. The fourth and fifth segments are dark at the distal end and light at the base. All the legs are uniformly golden-brown colored. Wings are pale at the base near the thorax and completely dark toward the rest of the abdominal segments, matching the distinctive feature of the body tone contrast. Males are slender, golden yellow, and smaller than females — nearly half the size at about 0.5 to 0.6 millimeters (Soto-Adames, 2020).

Biological Notes

The life cycle consists of six stages (Fig. 4): egg, two larval stages, prepupa, pupa, and adult. The length of the life cycle depends on the environmental factors (e.g., temperature and host plant). Thrips can complete their lifecycle in about 13 to 14 days on pepper plants grown in the greenhouse, although this period can be as long as 30+ days at lower temperatures (e.g., below 70 degrees F). Adults and immature (first and second larvae) thrips feed on softer leaf tissues of the plants, buds, petioles, and flowers. Adults and larvae tend to feed in the upper canopy, making the tender new growth most vulnerable to their injury and damage. Adults are commonly found on flowers.

The short-spined thrips are known to reproduce both sexually and asexually, laying individual eggs inside the leaf tissue. Males live, on average, for 6 days, while females live about 10 days. An adult female can lay about 15 eggs in its lifetime. After hatching from the eggs in 4 to 5 days, larvae undergo two active feeding instars (first instar: 1 to 2 days; second instar: 3 to 5 days). As these immature stages move across the leaf’s surface for feeding, they are responsible for most of the plant damage inflicted by the short-spined thrips. Larvae then molt into pre-pupae and subsequently to pupae in the soil/leaf litter after 4 to 5 days. Both pre-pupae and pupae stages are non-feeding, and they show movement only when disturbed. After 4 to 5 days on the soil, they emerge as adults and return to nearby host plants, where they feed on leaves, buds, flowers, pollen, fruits, and petioles.

Host Plants

Short-spined thrips are highly polyphagous. They feed on over 43 plants from 19 families, including peppers, beans, potatoes, strawberries, cucumbers, tomatoes, okra, coriander, papaya, sorghum, maize, and cotton. Chili peppers seem to be their preferred and main hosts. High infestations are also reported on other crops, including melon, cucumber, and squash. In ornamentals in greenhouses, short-spined thrips have been found on commonly cultivated plants such as hibiscus, marigold, mandevilla, ficus, gardenia, and gerbera. For a more complete list of reported host plants, see https://mrec.ifas.ufl.edu/lsolab/thrips/thrips-parvispinus/.

Plant Injury and Symptoms

The short-spined thrips causes severe deformations of leaves, flowers, fruits, and shoots; leaf scarring, flower drop, and leaf curling; as well as stunted growth. It causes serious damage to annual bedding plants (e.g., poinsettia and gerbera), as well as tropical plants (e.g., hibiscus, mandevilla, gardenia, anthurium, and hoya). White-flowered varieties are reportedly more susceptible to damage. In crops, especially peppers, T. parvispinus causes silver scarring on leaves that curl downward (Fig. 5). Fruits can also be misshapen and scarred. According to the European and Mediterranean Plant Protection Organization (EPPO), the short-spined thrips could potentially be a vector for melon yellow spot virus (MYSV), which can cause necrotic leaf spots on melon plants.

Management

The integrated management of the short-spined thrips in North America is developing as the pest spreads.

References