Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/22/2007
Publication Date: 6/1/2007
Citation: Suh, C.P. 2007. Head capsule widths of nymphal instars of the cotton fleahopper. Southwestern Entomologist. 32:127-130.
Interpretive Summary: Reassessment of treatment thresholds for the cotton fleahopper has been identified as a top research priority for cotton production in Texas. Consequently, several laboratories across the state are beginning to conduct fleahopper research studies, many of which require the ability to accurately determine the developmental progression (instar) of nymphs. Current guidelines for distinguishing the five nymphal instars are based on wing pad characteristics, but wing pads on earlier instars can be difficult to discern. As new scientists become involved in fleahopper research, there is a critical need for additional guidelines for distinguishing instars. The potential of using head capsule widths to determine instars was investigated by examining the range of head capsule widths within instars for both field-collected and laboratory-reared nymphs. Given that no overlap of ranges was observed for first, second, and third instars, these results indicated head capsule widths may be used to distinguish these earlier instars. Consequently, the ranges of head capsule widths reported in the study will provide additional guidelines for distinguishing nymphal instars and, more importantly, greatly improve the success rates of studies that require accurate assessments of nymph development.
Technical Abstract: Current guidelines for distinguishing the five nymphal instars of the cotton fleahopper are based on wing pad characteristics. However, wing pads on earlier instars can be difficult to discern, and distinctions among wing pad characteristics of these instars are rather subtle. Consequently, inexperienced observers often have difficulty determining the instars of nymphs. The potential of using head capsule widths to distinguish instars was investigated by examining the range of head capsule widths within instars for both field collected (cotton and horsemint plants) and laboratory-reared (green beans) nymphs. In general, nymphs collected from horsemint plants tended to have the greatest head capsule widths, while nymphs collected from cotton and those reared on green beans usually possessed similar head capsule widths. However, the ranges of head capsule widths within instars appeared to be similar among sources. Overall, head capsule widths of first instars ranged from 0.200 to 0.280 mm, second instars were between 0.313 and 0.375 mm, third instars were between 0.381 and 0.463 mm, fourth instars were between 0.450 and 0.569 mm, and fifth instars were between 0.550 and 0.669 mm. Given that the ranges of head capsule widths observed for first, second, and third instars did not overlap, the respective ranges reported herein should provide inexperienced observers additional guidelines for distinguishing earlier nymphal instars of the cotton fleahopper.