Effect of relative humidity on emergence and on dispersal and regrouping of first instar Nezara viridula (L.) (Hemiptera: Pentatomidae)

Laboratory studies with 1st instar of southern green stink bug, Nezara viridula (L.) indicated that relative humidity (RH) greatly affected nymph emergence and survivorship up to the 2nd instar, reaching the maximum value (approximately 90%) with RH of > 80%. At 60% RH, 60% of the nymphs emerged and survived, while with 0% RH only approximately 15% of eggs hatched, and most nymphs died. Emerged nymphs from egg masses placed in plastic boxes with a gradient of humidity remained on egg shells for ca. one day. After this period, they dispersed and regrouped on top of shells 6.8 +/- 0.67 times, until they abandoned the shells toward the source of humidity, avoiding the water-saturated areas. Duration taken for each rearrangement (dispersal + regroup) increased with time, with a range of approximately 26 min to 44 min. The mean duration of the grouping behavior on egg shells after each rearrangement decreased from approximately 102 min (1st) to 24 min (6th and last grouping). The rearrangement behavior of 1st instars on top of egg shells apparently compensates for the water loss of nymphs.