Searching responses of a hunting spider to cues associated with lepidopteran eggs

Authors: GALLAGHER, ROSA - Collaborator; Patt, Joseph - Joe; Pfannenstiel, Robert

Submitted to: Journal of Insect Behavior
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/2/2012
Publication Date: 5/31/2012
Citation: Gallagher, R.I., Patt, J.M., Pfannenstiel, R.S. 2012. Searching responses of a hunting spider to cues associated with lepidopteran eggs. Journal of Insect Behavior. 26:79-88. 2013.

Interpretive Summary: Cursorial spiders are a group of spiders that do not build webs, but instead run across foliage in search of their prey. They are important predators of the immatures and eggs of a number of crop pest insects, especially moths such as the corn earworm. The yellow sac spider (Cheiracanthium inclusum) is a common cursorial spider found in cotton and other row crops in south Texas. This spider has frequently been observed feeding on the eggs of the corn earworm and other moths. We examined the responses of this spider to the body scales and egg residues of corn earworm to determine whether these materials could signal the presence of eggs and help the spider locate moth eggs. We also made solvent extracts of corn earworm scales to determine if compounds present in the scales could be detected by the spider and trigger its searching behavior. A series of tests were conducted in which the spiders were presented with a piece of green florist paper that had been exposed to earworm scales alone or to scales plus egg residues or to untreated paper. A follow-up experiment was conducted in which the spiders were presented with solvent extracts of earworm scales or eggs. A range of polar to non-polar solvents was used to make the extracts; these included hexane, ethyl acetate, acetone, methanol and water. Contact with moth scales, egg residues, and extracts made with hexane and ethyl acetate triggered local searching behavior. Extracts made with polar solvents, such as water and methanol, did not trigger a response. These results strongly indicate that C. inclusum can perceive signal compounds left by corn earworms as they lay eggs and use these chemical cues to detect and locate moth eggs. Further studies of scale extracts with non-polar solvents are needed to identify these stimulatory compounds.

Technical Abstract: Cheiracanthium inclusum (Hentz), a cursorial spider, has been frequently observed feeding on the eggs of Helicoverpa zea (Boddie), an important cotton pest. This study investigated whether compounds present in H. zea scales and egg residues could act as kairomones and be used by C. inclusum in its prey searching behavior. A series of no choice tests were conducted in which the spiders were presented with a piece of green florist paper that had been exposed to H. zea scales alone or to scales + egg residues or untreated controls. A follow-up experiment was conducted in which the spiders were presented with solvent extracts of H. zea scales or eggs. A range of polar to non-polar solvents was used to make the extracts, these included hexane, ethyl acetate, acetone, methanol and water. In the experiments, contact with moth scales and moth scales + egg residues, as well as with non-polar solvent extracts of scales and eggs, resulted in retention and/or induction of local searching behavior in C. inclusum. Extracts made with polar solvents induced no apparent searching response. This indicates that the chemostimulatory compounds are lipophilic. These results strongly indicate that C. inclusum can perceive kairomones left by ovipositing H. zea and use these chemical cues to detect and locate H. zea eggs.