Effects of soil depths on nymphal eclosion of Melanoplus sanguinipes (Fabricius)

Authors: Pantoja, Alberto; Ranft, Richard; Fielding, Dennis; Hagerty, Aaron; Emmert, Susan

Submitted to: The Open Entomology Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/4/2013
Publication Date: N/A
Citation: N/A

Interpretive Summary: A large portion of Alaskan cropland is enrolled under the National Resources Conservation Service, Conservation Reserve Program land, most of which is located near Delta Junction to control wind erosion. CRP land may harbor considerable populations of grasshoppers that often invade nearby crops. Seven species of grasshoppers are common in interior Alaska. Three of the seven common species, Melanoplus borealis (Fieber), M. sanguinipes (Fabricius), and Camnula pellucida (Scudder), constitute a threat to crops. Considerable research has been conducted on grasshopper biology, ecology, competition, food quality, predators, pathogens, and population regulation of Alaska grasshoppers, but little work has been conducted on cultural practices (tillage, plowing) to manage grasshoppers in interior Alaska. There is a lack of understanding of how cultural practices can affect egg mortality and nymphal emergence. Cultural practices like plowing can affect soil and ambient temperatures which may delay hatching, slow nymphal development of influence egg mortality. The use of cultural practices is of particular importance in interior Alaska, since it is expected that insect, diseases, and weeds population will increase with climate change. The ability to control grasshoppers with cultural practices and the development of integrated pest management (IPM) tactics will be a major step toward controlling grasshoppers in Alaska. This work reports on the use of simulated cultural practices to influence grasshoppers nymphal emergence. The identification of cultural control is of interest to organic growers in Alaska. Grasshopper eggs were buried at depths of 2, 14, 18, 22, and 26 cm in laboratory arenas. Nymph eclosion ranges from 77 to 87%. However, nymph emergence, measured as the number of nymphs that reached the soil surface, was estimated at 80% when eggs were buried at 2cm, but was reduced to 2.5 % at 14cm depth. No nymphs emerged at depths of 22 cm or more. The relative high percentage of nymphal eclosion and the low or no nymph emergence suggest that the depths tested on this trial do not affect egg development and nymphal eclosion, but affect the ability of the insect to emerge to the soil surface, thus increasing first instar mortality. The addition of sand to the soil reduced nymphal emergence. A significantly lower percentage of hoppers emerged from sand as compared to soil, vermiculite, or soil mixed with 25, 50 and 75% sand. This suggests that cultural practices, such as plowing can be used as management tool to control grasshoppers.

Technical Abstract: This work reports on the use of cultural practices to influence grasshoppers nymphal emergence. Grasshopper eggs were buried at depths of 2, 14, 18, 22, and 26 cm in laboratory arenas. Nymph eclosion ranges from 77 to 87%. However, nymph emergence, measured as the number of nymphs that reached the soil surface, was estimated at 80% when eggs were buried at 2cm, but was reduced to 2.5 % at 14cm depth. No nymphs emerged at depths of 22 cm or more. The relative high percentage of nymphal eclosion and the low or no nymph emergence suggest that the depths tested on this trial do not affect egg development and nymphal eclosion, but affect the ability of the insect to emerge to the soil surface, thus increasing first instar mortality. The addition of sand to the soil reduced nymphal emergence. A significantly lower percentage of hoppers emerged from sand as compared to soil, vermiculite, or soil mixed with 25, 50 and 75% sand. This suggests that cultural practices, such as plowing can be used as management tool to control grasshoppers.