Seasonal Group Behavior of AdultJadera haematoloma(Hemiptera: Rhopalidae) in Central Florida Following Host Seed Exhaustion

Abstract

Jadera haematoloma Herrich-Sch?ffer (Hemiptera: Rhopalidae) is a specialist seed predator on Sapindales (Sapindaceae) and is common throughout North and Central America (Carroll & Loye 1987). In North-Central Florida J. haematoloma occurs on the recently-acquired host, the Goldenrain tree (Koelreuteria sp. Lax mann). Koelreuteria trees produce tens of thou sands of seeds in the canopy on floral rods after flowering in early fall. By mid-fall, seeds fall to the ground and are fed upon by J. haematoloma until the seed base is exhausted in early sum mer (Carroll & Loye 1987; Carroll 1988). Though dispersal morphs are common in other host populations of J. haematoloma, they are not favored in Koelreuteria populations due to the synchronous exploitation of Koelreuteria sp. seeds among host plants. Instead, non-repro ductive diapause in adults follows seed exhaus tion (Carroll et al. 2003). During this period from May to Sep 2009,1 observed adults forming dense, physically-touching groups in the canopy following the exhaustion of seeds. My goal was to determine the demographic composition of these groups and identify where they occur in time as well as their position within and among host trees. I observed individuals foraging on seeds on the ground around host trees in large aggrega tions through late May and early Jun in the northwest Gainesville area (Alachua County, FL) in the manner described by previous investi gators (Carroll & Loye 1987). Following seed ex haustion and a noticeable decline in the density of individuals on the ground, I completed an ex tensive survey of the canopy and surrounding ground area of 12 large Koelreuteria trees using binoculars and a spotting scope to view higher canopies. Trees were classified according to their seed productivity, branching, height, and trunk diameter to determine if these influenced group number or insect abundance. Seed productivity was estimated by counting the number of bare floral rods in the canopy as a proxy for the num ber of seed-yielding flowers produced the previ ous fall. Samples of seeds were collected from the ground at each tree to verify seed exhaustion (af ter Carroll et al. 2003). I defined a group of bugs as 10 or more stationary individuals spaced less than 2 body lengths apart from one another (Fig. 1) in hopes of avoiding confusion with the ground foraging aggregations around host plants pre viously described in Jadera literature (Carroll & Loye 1987). To determine whether groups were randomly distributed around host trees, I re corded the branch position, compass position rel ative to trunk, height, radius from the trunk, and number of participating insects for each ob served group; a picture was taken to verify counts and each group was assigned a number. One quarter of the number of groups was ran domly selected based on a random numbers ta ble and then destructively sampled using a bag net at each tree. Sex ratios within groups were estimated for each tree from the collected group(s). Statistical analyses were conducted with JMP (SAS institute 2008). In total, 46 groups were observed. Fewer than 20 individuals were observed on the trunk or ground of any given tree during sampling. Trees contained between 0 and 17 groups within the canopy (mean = 4.6). The proportion of terminal branches with florescence rods (a proxy for seed productivity) reliably predicted the total number of individuals found on a tree (ANOVA, df= 45, F = 37.29, = 0.0005) and the number of groups within a tree (ANOVA, df = 8, F = 7.14, = 0.0319). Three trees without insects were ex cluded from the following analyses of group loca tion and participation. Group positions were bi ased towards more terminal branches as de scribed by Strahler and Botanical branch order ing systems (Strahler 1957; Wilson 1966, Fig 2). Number of branch meet-ups from most terminal branches (Strahler) was biased towards terminal branches, but position was not biased in the num ber of branch meet-ups from the trunk (Botani cal). This is contrary to the expectation that groups are more likely to occur in positions on the tree which are more abundant, which would bias the number of groups both towards most terminal branches, and branches furthest from the trunk, as more positions are available at the exterior of the crown. These data show that bugs are distrib uted in terminal sites regardless of where termi nal sites occur within the crown. The distribution