Activity of Rubidium and Cesium in Soybean Looper (Lepidoptera: Noctuidae): Insect Feeding on Cotton and Soybean Measured by Elemental Markers

Abstract

Uptake and translocation of the elemental markers rubidium (Rb) and cesium (Cs) within adult soybean looper, Pseudoplusia includens (Walker), were determined using atomic absorption spectrophotometry in the laboratory in various feeding and mating treatments. Neonates were tested to determine marker transfer from male and female adults fed rubidium chloride (RbCl)-treated artificial nectar, cesium chloride (CsCI)-treated artificial nectar, or both. All females contained detectable levels of Rb, Cs, or both, which were obtained either through direct feeding or via spermatophores. Rubidium was present in females at significantly greater levels than Cs. No significant differences in Rb levels were observed between feeding or spermatophore acquisitions. Most neonates had significantly higher levels of Rb than Cs. In a field cage study to evaluate adult feeding and oviposition behavior on blooming cotton and blooming soybean treated with RbCl and CsCl, respectively, more eggs contained Rb than Cs, indicating greater feeding on cotton nectar than soybean nectar, regardless of the host plant upon which eggs were laid. Females laid more eggs on blooming soybean than on blooming cotton. Higher levels of Rb in cotton than Cs in soybean were recorded and may be attributed to initial elemental marker quantities available to the insects. This study provides the support for the generalized observations that soybean looper infestations in soybean can be related to feeding activities by adults in cotton.

Evaluation of Rubidium Chloride and Cesium Chloride Incorporated in a Meridic Diet to MarkDiatraea grandiosella(Lepidoptera: Crambidae) for Dispersal Studies

“…Many of the eggs may have been laid before the females mated. Low egg viability was reported in the soybean looper, Pseudoplusia includens (Walker), where adults were fed artiÞcial nectar containing 190 g/g RbCl or CsCl (Jost and Pitre 2002). However, most other lepidopterans treated with Ͼ1000 g/g Rb or Cs mate successfully (Stimmann et al 1973;Graham and Wolfenbarger 1977;Van Steenwyk 1982, 1984;Hayes and Reed 1989).…”

“…There should be little decay of Rb and Cs concentrations. The absence of feeding also reduces the risk of marker loss through excretion (Chapman 1982, Jost andPitre 2002).…”

“…Improved instrumentation with lower detection limits may be required to detect Rb and Cs transferred by mating. Horizontal (mating) and vertical (oviposition) transfer of Rb and Cs has been reported for several lepidopterans: tobacco budworm Wolfenbarger 1977, Hayes andReed 1989), pink bollworm (Van Steenwyk et al 1978), cabbage looper (Moss and Van Steenwyk 1984), and soybean looper (Jost and Pitre 2002). However, the exact reasons for the transfer of these elements in various species needs further study.…”

“…Rubidium (Rb) and cesium (Cs) have been used to mark insects physiologically (Berry et al 1972;Van Steenwyk 1982, 1984;Fernandes et al 1997;Prasifka et al 2001;Jost and Pitre 2002). Moss and Van Steenwyk (1984) pointed out that Rb and Cs could be used in dispersal experiments to give three (Rb, Cs, and Rb/Cs) distinct markers.…”

“…Akey (1991) and Hagler and Jackson (2001) reviewed the uses, successes, and problems associated with RbCl and CsCl to mark insects. In biological systems, Rb and Cs are not very toxic because they mimic potassium, which is present in reasonable concentrations in plant and animal tissues (Berry et al 1972, Moss and Van Steenwyk 1982, Jost and Pitre 2002. Physiological markers are not visible, but they can be detected with appropriate instrumentation.…”