Showing papers by "Erin W. Hodgson published in 2007"

Economic threshold for soybean aphid (Hemiptera: Aphididae)

Abstract: Soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), reached damaging levels in 2003 and 2005 in soybean, Glycine max (L.) Merrill, in most northern U.S. states and Canadian provinces, and it has become one of the most important pests of soybean throughout the North Central region. A common experimental protocol was adopted by participants in six states who provided data from 19 yield-loss experiments conducted over a 3-yr period. Population doubling times for field populations of soybean aphid averaged 6.8 d ± 0.8 d (mean ± SEM). The average economic threshold (ET) over all control costs, market values, and yield was 273 ± 38 (mean ± 95% confidence interval [CI], range 111–567) aphids per plant. This ET provides a 7-d lead time before aphid populations are expected to exceed the economic injury level (EIL) of 674 ± 95 (mean ± 95% CI, range 275–1,399) aphids per plant. Peak aphid density in 18 of the 19 location-years occurred during soybean growth stages R3 (beginning pod formation) to R5 (full size pod) with a single data set having aphid populations peaking at R6 (full size green seed). The ET developed here is strongly supported through soybean growth stage R5. Setting an ET at lower aphid densities increases the risk to producers by treating an aphid population that is growing too slowly to exceed the EIL in 7 d, eliminates generalist predators, and exposes a larger portion of the soybean aphid population to selection by insecticides, which could lead to development of insecticide resistance.

Field Validation of Speed Scouting for Soybean Aphid

Abstract: Agricultural professionals are spending increasing amounts of time making treatment decisions for soybean aphid, Aphis glycines Matsumura. In an effort to reduce the time required to make treatment decisions, a binomial sequential sampling plan called "Speed Scouting" was developed for soybean aphid. In 2005, we validated Speed Scouting using commercial fields in Minnesota and replicated small plot trials in four states in the North Central Region of the USA (Iowa, Michigan, Minnesota, and Wisconsin). In commercial fields, yield (bu/acre ± S.E.) was significantly higher in areas of the fields where treatment was applied based on Speed Scouting (50.7 ± 1.7) compared to untreated controls (46.9 ± 1.6). When comparing treatment decisions based on Speed Scouting and whole-plant counts, the same decision was reached 79% of the time. Results from 5 of the 6 small plot trials showed no significant yield difference when aphid control decisions were made using Speed Scouting compared to whole-plant counts using an economic threshold of 250 aphids per plant. Speed Scouting is a conservative sampling plan, and consistently recommended treatment before populations reached the economic threshold using whole-plant counts. Using either sampling method, soybean aphid management should rely on multiple samples over time to accurately assess population growth rates to avoid unnecessary foliar applications.

Cereal Leaf Beetle

Abstract: The cereal leaf beetle feeds on a wide range of host grasses, both in the larval and adult stages. This insect prefers spring-seeded small grains, especially barley, wheat and oats, but will also feed on spelt, wild oats, orchardgrass, timothy canarygrass, reed canarygrass, annual ryegrass, perennial ryegrass, foxtail, and fescues. Adult cereal leaf beetles may feed on the leaves of corn, sorghum, and sudangrass. Plants that are least preferred by the beetles but can still serve as a host plant include, bluegrass, millet, fescue, red brome, red top, and downy brome. In general, beetles prefer young plants and younger growth on plants. Cereal leaf beetles are rarely found on broadleaf plants.

Aphids in Alfalfa

Abstract: Aphids have piercing sucking mouthparts and remove phloem or plant sap juices with a flexible stylet (Fig. 1). Wingless aphids are not very mobile insects, and tend to stay on one plant. As a result, some plants can become heavily infested as the colony grows over time. Winged aphids locate potential hosts by using visual cues, and will often quickly probe plant tissue before settling to feed. As aphids pierce plant tissue, the stylets pick up small virus particles. Aphids can then vector, or transmit, plant diseases persistently or non-persistently.

Beneficial Insects: Mantids

Abstract: Mantids are closely related to grasshoppers, crickets and katydids, and go through simple or incomplete metamorphosis (Fig. 2). There is one generation per year. In the fall, mated females will deposit 2-400 eggs in a frothy protective egg case called an ootheca (Fig. 3). Oothecae harden on branches, rocks, or other structures, and are the overwintering stage. In the spring, nymphs will emerge from the ootheca and immediately begin to look for food. Often, mantids are cannibalistic and will eat siblings. Nymphs mature into adults later in the summer.

Lygus Bug in Alfalfa Seed

Abstract: Lygus bug, Lygus lineolaris, is a true plant bug in the family Miridae (Fig. ). Sometimes this insect is also called tarnished plant bug. Lygus bug is native to North America and is distributed throughout Mexico, United States and Canada. Western tarnished plant bug, L. herperus, is closely related to the lygus bug and has overlapping distributions in the western United States. Lygus bug has a wide host range of more than 350 plants and is considered damaging wherever it occurs. In general, lygus bug prefers crops, vegetables, and weeds near crops. In Utah, lygus bug is considered the main pest of alfalfa seed production. Heavy feeding on all the growing points (e.g., buds, flowers, pods) can severely reduce seed yield potential.

Beneficial Insects: Beetles

Abstract: Beetles belong in the largest insect order Coleoptera and go through complete metamorphosis (Fig. 3). Mated females lay football-shaped eggs, usually starting off nearly colorless, but eventually turning dark yellow or brown. Eggs hatch into mobile larvae; often larvae are the predatory life stage and will eat soft bodied insects like aphids. Larvae go through several molts before transforming into a resting pupae. Adults emerge from pupal cases with functional wings and reproductive organs. Adults can be carnivores or herbivores. The total development time to adulthood is dependant on the temperature and beetle species. Beetles typically have one generation per year, but some species can have three or more per year. Fig. 2. Rove beetles can be beneficial insects.2 What You Should Know

Yellowjackets, Hornets, and Paper Wasps

Abstract: Social wasps, including yellowjackets, hornets and paper wasps, are common stinging insects in Utah (Figs. 1, 2). The wasps are related to ants and bees, which are also capable of stinging; however, yellowjackets are the most likely to sting. Less than 1% of people are allergic to wasp or bee stings; however, some people are fatally stung every year. Nearly 80% of all serious venom-related deaths occur within one hour of the sting. Most people will only experience a mild local reaction with redness, pain, swelling and itching at the sting site. If symptoms are more serious, a physician should be consulted. Some people may develop venom sensitivity after repeated stinging episodes over a short or long period of time. Fig. 2. Baldfaced hornet.2

Beneficial Insects: True Bugs

Abstract: True bugs, and all Hemipterans, go through simple or incomplete metamorphosis. Males and females will mate end-to-end (Fig. 3), or facing away from each other. Mated females lay eggs singly or in small masses near potential food sources. Nymphs hatch from the eggs and begin to search for small prey items. Nymphs look similar to the adults except they are smaller in size and lack functional wings; nymphs will develop wing pads as they mature. They pass through five instars before finally molting into an adult. Total development time is dependant on the weather, but generally there are several generations per year. Fig. 2. Bee assassin bug adult.2 What You Should Know