Rice Delphacid

Description 

The Rice Delphacid (RD), Tagosodes orizicolus, is a planthopper, typically about ¼ inch long (Fig. 1a). It exhibits sexual dimorphism, with females being larger than males. Males are brown with black patches at the tips of their wings, while females are paler in color (Fig. 1a). Both sexes have a yellow-to-white median dorsal stripe.

There is also a short-winged female morph, where the wings are significantly smaller, and the abdomen is more bulbous (Fig. 2a). These short-winged females primarily focus on egg-laying (Fig. 2b) when resources are available, aiding in the rapid establishment and growth of the population. 

The RD undergoes five nymphal instars before maturing into adults. Nymphs are lighter in color than adults and have two characteristic brown stripes on each side of the abdomen (Fig. 1b). They are smaller and lack wings. Both adults and nymphs have piercing-sucking mouthparts, which they use to extract sap from rice plants.

As an adult, the RD resembles a leafhopper, but can be distinguished by its large, apical, hind leg spur. Planthoppers, like the RD, have a prominent spur on their hind legs (Fig. 2d), whereas leafhoppers only have one or two rows of smaller spines.

Preferred Hosts

Rice delphacids (RDs) feed on various grasses in the Poaceae plant family, with rice being its primary and most economically significant host. While this insect has been observed on other monocots such as barnyard grass and various non-crop grasses, rice remains its most severely affected host. 

Key Facts

• Piercing and sucking insects that feed on rice plant phloem.
• Invasive pests in the U.S. from Central and South America.
• Cause leaf damage known as “hopperburn.”
• Symptoms of damage include yellowing of leaves and ovipositional scars on leaf blades.
• Excrete excess sugar called “honeydew,” leading to sooty mold.
• Carry a virus that causes rice hoja blanca disease.
• First recorded in Texas in 2015 and have since spread throughout the Texas Rice Belt.

Life Cycle

The life cycle of a RD (Fig. 3) from egg to adult lasts 4 to 6 weeks, depending on the temperature. A RD lays eggs by inserting its ovipositor into the leaf sheath or midrib of rice leaves (Figs. 1c and 3).

Eggs are typically laid in clusters and hatch after 5 to 11 days (about 160 per female lifespan). The nymphs undergo five instars over 15 to 25 days, feeding and growing until they reach adulthood.

First instars are about 0.5 to 0.7 mm long, and are white with red eyes. As the nymph develops through instars, the body becomes light yellowish and develops a pair of dark brown longitudinal stripes.

Adult delphacids continue to feed on plants, mate, and lay eggs for 15 to 36 days. 

Injury/Damage

The feeding behavior of the RD causes both direct and indirect damage to rice plants, severely impacting crop health and yield. 

Direct Damage

Both nymphs and adults extract sap from plant phloem, depriving plants of essential nutrients. Nymphs and adults inhabit distinct areas of the rice plant, with nymphs feeding on the lower stems and adults feeding higher up on the plant. This feeding activity results in symptoms such as leaf senescence, necrosis, and a condition known as “hopperburn” (Fig. 4). Hopperburn typically begins with yellowing at the leaf tips, which progresses to browning and drying as infestations intensify. In severe cases, this can lead to extensive plant dieback, stunted growth, and substantial yield losses. 

In addition to the physical damage, RD excrete honeydew, a sugary substance that promotes the growth of sooty mold on leaves (Fig. 5). The sooty mold forms a black coating over the leaf surface, reducing a plant’s ability to photosynthesize effectively. This further weakens the plant, compounding the stress caused by direct sap loss. 

Indirect Damage

The RD is the primary vector of the Rice Hoja Blanca Virus (RHBV), a serious pathogen causing Rice Hoja Blanca or “white leaves” Disease (Figs. 6 and 7). Infected plants can experience reduced tillering, stunted growth, and severe yield losses. 

Monitoring

Effective monitoring of RD is essential for managing infestations and minimizing crop damage. To ensure early detection, regular field inspections are needed, paying particular attention to early signs of RD activity such as yellowing of leaves, sooty mold, and hopperburn symptoms. Use sweep nets to assess both nymph and adult populations, with a focus at the bottom canopy of rice plants where RD nymphs are most commonly found. 

Since RD pose the greatest threat during the vegetative stage, monitoring should begin at the early tillering stage of rice. Ratoon rice seems to be more susceptible to RD in Texas. Therefore, it is important to monitor ratoon fields closely to prevent significant yield loss. 

Management

There is no established economic threshold for RD. Currently, two insecticides, Endigo ZCX and Tenchu 20SG, are labeled under emergency exemptions for RD control in Texas, with registrations valid until 2025. When using these pesticides, follow label instructions in conjunction with the emergency exemptions. Remember, the label is the law! 

In native countries of the RD, the main strategy for managing them involves using resistant or tolerant rice varieties. In the U.S., research is underway aiming to better understand the susceptibility of various rice cultivars to RD. Integrating varietal resistance with other IPM strategies, like cultural practices and chemical controls, can create a sustainable and effective approach to controlling RD. 

Ratoon fields should be monitored rigorously, especially in late September through October when ratoon rice is in the reproductive stages. Historically, this time of year is when the majority of RD infestations occur across the state. Fields should also be scouted rigorously in the weeks following rainfall events.