Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/8/2011
Publication Date: 2/1/2012
Citation: Srygley, R.B. 2012. Age- and density-dependent prophylaxis in the migratory Mormon cricket Anabrus simplex (Orthoptera: Tettigoniidae). Environmental Entomology. 41(1): 166-171.
Interpretive Summary: When insects are crowded, diseases are more likely to be transmitted from one individual to another. To maximize survivorship when crowded, insects might increase their readiness to fight infection. In nature, Mormon crickets can be solitary, non-migratory individuals or they can be in dense migratory bands. I asked whether Mormon crickets reared at densities similar to those in migratory bands would have higher levels of immune activity when compared to those from the same population that were reared solitarily. I assayed immune activity by measuring three important immunity enzymes – phenoloxidase, prophenoloxidase, and antibacterial, lysozyme activities. In addition, I measured the rate of encapsulation of glass rods inserted into the insects’ abdomen. I did not find any differences in enzyme or encapsulation activities between Mormon crickets from the two rearing environments early in their adult stages. However later when the Mormon crickets were nearing reproductive maturity, I found greater levels of prophenoloxidase and encapsulation activity in those reared in groups relative to those reared solitarily. Anti-bacterial activity remained similar between the two rearing environments. Thus the Mormon crickets responded to crowding by increasing some of their constitutive immune defenses but not others and only at older ages.
Technical Abstract: As a result of the increased potential for disease transmission, insects are predicted to show an increased constitutive immunity when crowded. Nymphal Mormon crickets were collected in Montana and reared in the laboratory either solitarily or at densities similar to that experienced by Mormon crickets in migratory bands. As teneral adults, solitarily-reared Mormon crickets tended to have greater phenoloxidase activity than those reared in groups. Sampling enzyme activity a second time when the adults were nearing reproductive maturity, group-reared Mormon crickets had elevated levels of prophenoloxidase and encapsulated foreign objects faster than solitarily-reared insects. Rearing density did not have a significant effect on either the darkness of the cuticle or anti-bacterial activity. This is the first report of age-related responses of adult insect immunity to crowding.