Soil and Moisture Relations of Scaptocoris divergens Froeschner (Hemiptera: Cydnidae)

This Neotropical, fossorial bug feeds on the roots of banana and other plants. In laboratory experiments it penetrated light soils more rapidly than heavy soils, but extremely dry and very wet soils were not penetrated and the insect survived exposure to excessive water rather poorly. Although starved insects survived rather well in moist soil, those removed from soil lost water rapidly and became desiccated in a few hours. In vertical chambers containing uniformly moist soil, both sexes responded positively and strongly to gravity; in both vertical and horizontal chambers, each containing two samples of soil that differed only in moisture content, both sexes responded positively and strongly to moisture. When S. divergens was presented with conflicting stimuli in vertical chambers (moist soil above the interface, dry soil and gravity below), both sexes reacted positively toward moisture, temporarily becoming negatively geotactic in this situation. The intensity of the moisture response was directly related to the difference in moisture content between the alternative soils, and inversely related to the moisture content of the drier soil. In horizontal chambers the mean distances that the insects moved from the interface into alternative moist and dry soils were not significantly different, which indicates that differences in soil consistency, as affected by moisture content, did not bias the insects' response to soil moisture. By ablation of successive antennal segments, the moisture receptors were localized on antennal segments 3 and 4 in the male and 1 through 4 in the female. With both sexes the intensity of the reaction was a function of the number of receptor-bearing segments remaining on the antennae. Specific moisturesensitive sensilla were not identified.