Thwart grasshopper attacks with cultural practices and well-timed insecticides

Removing habitats such as weedy areas and timing insecticide applications accordingly may provide some regulation of grasshopper populations. photos courtesy of Ray Cloyd.“The Beginning of the End” is the title of the classic 1950s science-fiction movie staring Peter Graves (Mission Impossible fame) about gigantic locusts/grasshoppers that take over Chicago. Do you ever feel like they’re taking over the nursery?
 
There are many different types of grasshoppers including migratory, grassland and clear-winged. Grasshopper species that may be encountered feeding on plant material in greenhouses or outdoor nurseries are the migratory (Melanoplus sanguinipes), differential (M. differentialis), redlegged (M. femurrubrum), twostriped (M. bivittatus) and western lubber (Brachystola magna) grasshopper. Grasshoppers can be damaging and difficult to manage in indoor and outdoor production systems.

Biology
After mating, female grasshoppers feed for approximately two weeks before they initiate egg-laying, which usually occurs from summer through fall. Eggs, which are laid in pods containing less than 50 eggs, can be deposited in many different habitats including weedy areas and around the base of plants. Eggs hatch over a three to four week period; however, this varies depending on the species.
 
Eggs are deposited under the soil in pod-like structures. Compact, loamy soils are preferred by females for egg-laying. Each pod may consist of 20 to 120 elongated eggs, which are cemented together. Females can produce between eight to 25 egg masses during their lifetime. Temperature, moisture content and pH of the soil must be favorable in order for eggs to develop properly.

Most grasshopper species overwinter as eggs while some species may overwinter as nymphs. Egg development requires soil temperatures less than 50ºF. Eggs hatch in April through May with a majority of the young grasshoppers emerging from June through July. Young grasshoppers are called nymphs and resemble adults; however, they are smaller, have fewer antennal segments and possess wing pads instead of wings. Depending on the species, there may be four to six nymphal instars. The entire nymphal period takes 25-30 days. Each nymphal instar takes four to five days to complete with the exception of the final nymphal instar, which is completed in seven days. The life cycle from egg to adult takes from 40 to 60 days; however, this is contingent on both ambient and soil temperatures. Adults may live for up to 50 days.

Adult grasshoppers may live for up to 50 days.

The grasshopper's rapid jumping ability allows it to escape predators and avoid insecticide contact.

Feeding
Grasshoppers have chewing mouthparts, which are used to create distinct ragged, serrated damage on plant leaves and flowers. Due to their mobility, grasshoppers can migrate into areas and consume any type of plant material, including trees, shrubs, herbaceous annuals and perennials and vegetables. And grasshoppers can fly for several miles. Grasshopper abundance is very much dependent on weather (temperature in particular), soil type and vegetation. Also, nymphs and adults may be present in the same habitat simultaneously. Grasshoppers are more active on warm, sunny days and climb onto plant material feeding on leaves, flowers and unopened buds. They prefer to feed on young green leaves, which are a higher source of nutrition, and tend to avoid old, yellowing leaves.

Management
Removing weeds from around the production area will at least eliminate habitats where grasshopper females may lay eggs. The characteristic rapid jumping ability of grasshoppers allows them to escape predators and avoid contact from insecticide sprays. Recommended insecticides include permethrin, carbaryl, clarified hydrophobic extract of neem oil, malathion, petroleum-based oils and spinosad. There are two problems associated with attempting to regulate grasshopper populations with insecticides: their ability to jump and disperse; and the hardened cuticle (skin), which may prevent or reduce penetration of insecticides into the body. However, young nymphs may be easier to kill due to a thinner cuticle than adults.

Grasshoppers are more active on warm, sunny days and climb onto plant material feeding on leaves, flowers and unopened buds.Nosema locustae
Another management option is Nosema locustae.
 
N. locustae is a protozoa that when activated (by ingestion) consumes the fat reserves in grasshoppers, and any remaining reserves are not sufficient to nourish the nymphs during the molting process. This also inhibits maturation and reproduction resulting in reduced vigor and egg-laying activity. It has been demonstrated that infected females produce fewer eggs than non-infected females. The protozoa can be transmitted through the eggs to offspring (transovarial transmission). The active ingredient is sold commercially in products such as Semaspore Bait and Nolo Bait and is formulated on a wheat bait.
 
Grasshoppers must consume the spores to be negatively affected. The material may cause a minor reduction in grasshopper populations after several weeks; however, this material will not provide an immediate reduction in the population. Grasshopper age and population density may influence how effective Nosema is on the overall population. The primary way by which N. locustae is distributed among grasshopper populations is by the scavenging of infested cadavers by healthy grasshoppers.

Control is in reach
Grasshoppers are one of the most difficult insect pests to deal with in both indoor and outdoor production systems, and they can cause considerable damage to many different types of plant material. However, removing habitats such as weedy areas and timing insecticide applications accordingly may provide some regulation of grasshopper populations. In most cases, it may not be the “Beginning of the End.”

Ray Cloyd is associate professor and extension specialist in ornamental entomology/integrated pest management, Kansas State University, rcloyd@ksu.edu.