Development of Methods for Testing Alterations in Flight Behavior of Cry1Fa-Resistant and Susceptible Spodoptera frugiperda in Response to Feeding on Cry1Fa Protoxin
Hietela, L.  2018.  M.S. Thesis.

The fall armyworm (Spodoptera frugiperda, Lepidoptera: Noctuidae) is an important agricultural pest of corn, cotton, soybean, and a number of other American specialty and row crops. The annual life cycle of this insect in the United States involves a seasonal migration during the growing season from overwintering locations in Florida and Puerto Rico, and Texas and Mexico, to northern regions of the United States and southern Canada. Control of this insect in corn is generally achieved through the use of transgenic varieties producing a transgene coding for the Cry1Fa insecticidal protein derived from the bacterium Bacillus thuringiensis (Bt). The exposure of populations of S. frugiperda to Cry1Fa toxin has led to several instances of field-evolved resistance to corn producing this toxin and lack of appropriate control. In a related species, Spodoptera exigua (Lepidoptera: Noctuidae), exposure to the marginally effective toxin Cry1Ac has been shown to reduce pupal weight, but increase flight behavior. This study is intended to determine the relationship between exposure of Cry1Fa-resistant S. frugiperda to that toxin and flight behavior as compared to unexposed and susceptible insects. In addition, in order to determine physiological effects of resistance and exposure to sublethal toxin doses, the phospholipid profiles of susceptible and Cry1Fa-resistant S. frugiperda exposed to control of Cry1Fa-containing diet. Determining the effect on flight behavior and capacity of these insects will further the understanding of resistant insect interactions with Cry toxin pesticides, and particularly the effects that these toxins have on resistant insect behavior and physiology. This study shows that Cry1Fa-resistant S. frugiperda larvae feeding on diet containing Cry1Fa do not have a significantly different flight behavior than those feeding on untreated diet. Flight behavior in this study was positively affected by pupal weight (p=0.0081). Analysis of phospholipids in S. frugiperda abdomens determined that the Cry1Fa-resistant strain did not display a significantly different phospholipid profile (p=0.1089), and that those insects reared on corn (Zea mays) had greater detected phospholipid levels (p=0.0002), while Cry1Fa-resistant insects exposed to Cry1Fa toxin did not express altered phospholipid levels (p=0.3738).