Project Summaries

12-434SC  Project Manager: P. F. O'Leary

CAN WE ENHANCE THE IMPACT OF NATURAL ENEMIES OF STINK BUGS IN COTTON?

Francis P. Reay-Jones, Clemson University

Once considered secondary pests in cotton, stink bug damage and abundance on cotton in the Southeast U.S. have greatly increased in recent years. Because of the widespread pest status of stink bugs across multiple crops in the United States, particularly in the Southeast, it is imperative that pest managers develop a better understanding of stink bug biology and develop alternative management strategies to mitigate yield and fiber quality losses while reducing the number of broad spectrum pyrethroid or organophosphate insecticides used to manage these pests.

In addition to chemical control, there are some natural control mechanisms for stink bugs. A complex of parasitoids and predators is known to impact stink bug populations in the United States. Parasitoids use odorous cues emitted from stink bugs to find and parasitize them, and predaceous arthropods either use the same cues or more visual/tactile cues (or a combination of cues). IPM programs need to maximize the impact of beneficial insects. The feeding of insects on plants is known to induce releases of volatile chemicals from the plants that can both stimulate plant defense and attract natural enemies. Laboratory trials have shown that feeding by the southern green stink bug on cotton and corn can increase the emission of plant volatiles. Studies with plant volatiles can lead to the development of alternative tools to broad spectrum insecticides in pest management programs. Plant volatiles have potential to reduce pest populations when applied to crops by enhancing the natural control of pests.

Jasmonic acid is a common herbivore-induced plant volatile and is a potent plant hormone responsible for a variety of physiological functions including growth, development, and defense signaling against herbivores. Few studies have tested the effectiveness of using jasmonic acid in field trials, as most efforts have focused on laboratory and greenhouse experiments. Preliminary work was conducted in 2009 showed that stink bug egg predators can reduce egg numbers by 40% under field conditions, and that applications of jasmonic acid may increase predation by 35%. This work was limited to a single cotton field in 2009 and needed to be expanded.

Studies were conducted at the Clemson University Pee Dee and Edisto RECs in Florence and Blackville. Stink bug colonies were initiated (Florence) or increased (Blackville) to provide sufficient numbers of egg masses. Collections began in April in wheat fields. Egg masses from laboratory-reared stink bug colonies (brown or southern green stink bugs) were deposited on paper cards or cheesecloth and held at -20°C (Blackville) or -80°C (Florence) until field experiments begin. Eggs were counted in each mass before placement in the field. A 0.5-mM solution of jasmonic acid was prepared in 1 mL of acetone and mixed in water. Each treated plant was misted with approximately 1 mL of the JA solution (0.105 mg JA/plant) using a spray bottle. Control plants were misted with 1 mL of acetone/water solution. Stink bug egg masses were placed in a cotton field at each REC by stapling index cards or cheesecloth to the underside of cotton leaves in a randomized complete block design. Each block (n = 5 replications) consisted of two plots of 12 rows by 80 ft. Within a plot, 2 egg masses were attached with a paper clip to cotton leaves in row 6 at 30 and 50 feet into the plot. Plants with egg masses and the four surrounding plants were treated with either the jasmonic acid solution or an acetone control solution. Egg masses were collected three days following placement in field, the number of missing and sucked dry egg masses were recorded, and those remaining were placed in plastic cups with ventilated lids and held in an insect growth chamber to monitor any parasitism. Pitfall traps with antifreeze were placed in each plot when eggs were placed in the field and were collected after 7 days to identify potential predators.

Surprising, very little predation was observed in the trial in Florence. Out of 1,192 brown stink bug eggs stapled to cotton leaves in Florence, only 64 were removed during the trial, presumably by predators. Applications of jasmonic acid did not impact predation. A total of 473 southern green stink bug eggs were stapled to cotton leaves in Florence and none were preyed upon. A possible reason is the unusual rainfall that occurred, with heavy rain occurring every week of the trial. This could have washed out predators from the field and prevented predators from finding stink bug eggs. Some of the pitfall traps placed in the field were full of sand, which is indicative of heavy rain.
No insecticides were used on cotton in this trial to maximize populations of natural enemies. Pitfall trap samples caught mainly fire ants, big-eyed bugs, crickets, and sap beetles, though numbers were always low. Other studies have shown that fire ants, big-eyed bugs, and lady beetles can prey on stink bug eggs. Stink bug eggs that were stapled to leaves in the field were bought back to the laboratory to assess egg parasitism in environmental chambers. No parasitoids emerged from the eggs. In addition, no stink bugs were sampled in sweep net samples. Future work should continue to investigate the use of plant volatiles as alternatives to broad spectrum insecticides.

 

Project Year: 2012
 

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