General observations

The following outline condenses the large number of figures and tables found in this publication into general groupings for the convenience of the reader.

A total of 57,129 Phyllophaga individuals were examined and identified in the course of this study. The 215 captured females represented only 0.38% of the total catch, suggesting that the attractants do not function as aggregation pheromones in any of the species. A total of 145 males were counted from the control traps, amounting to only 0.25% of the total catch.

No Phyllophaga beetles were captured in Aggasiz, British Columbia; Bandon, Oregon; or Homestead, Florida. In British Columbia and Oregon, the traps were located at cranberry bogs. A light trap operated at the Oregon cranberry bog site also captured no Phyllophaga. Despite extensive sampling for root weevils in northwest commercial cranberry bogs, no white grubs have been reported (D. C. Weber, unpublished data). Moreover, when the Phyllophaga species distribution maps in Luginbill and Painter (1953) are examined, only four species of Phyllophaga are found listed from Oregon. Regarding the Homestead, Florida site, Woodruff (1961) indicates that very few of the Florida Phyllophaga species occur in Miami or in the Florida Keys. In the same publication, he points out that “The soil in the Miami area is extremely shallow and underlain by öolitic limestone and, in general, is not a good soil for white grubs.” Only 4 of the 42 species of Phyllophaga recorded from Florida have been collected in that area.

Tables 2a and 2b list alphabetically thePhyllophaga species captured, the number of males captured in each species, the number of discrete locations at which they were captured, and the total number of site-years for each species [site-years = (site A x number of years that species was captured at that site) + (site B x number of years that species was captured at that site) + .......]. Tables 3a and 3b are sorted by descending catch numbers, beginning with thePhyllophaga species caught in the greatest number. Tables 4a and 4b are sorted by site, listing in descending order the number of sites at which a particular species was recorded.

Table 2a

Male catches, sites, and sites-years sorted by species.

Table 2b

Male catches, sites, and sites-years sorted by species.

Table 3a

Male catches, sites, and sites-years sorted by n.

Table 3b

Male catches, sites, and sites-years sorted by n.

Table 4a

Male catches, sites, and sites-years sorted by sites.

Table 4b

Male catches, sites, and sites-years sorted by sites.

Of all site-years when and where beetles were captured, only two (NJ Chatsworth #2, 1999 Table 59 and UT Salt Lake City, 1999, Table 91) recorded a single species of Phyllophaga during a flight season. The average number of species captured during a site-year was 4.15. Three sites (AL Auburn, 1998, Table 6; KS Manhattan #1, 2000, Table 27; and KS Manhattan #2, 2001,Table 28) recorded more than 10 species of Phyllophaga captured during the flight season.

Table 59

New Jersey, Chatsworth #2 1999

Blends indicate the ratio of the methyl esters of L-valine/L-isoleucine

Table 91

Utah, Salt Lake City 1999

Blends indicate the ratio of the methyl esters of L-valine/L-isoleucine

Table 6

Alabama, Auburn 1998

Blends indicate the ratio of the methyl esters of L-valine/L-isoleucine

Table 27

Kansas, Manhattan #1 2000

Blends indicate the ratio of the methyl esters of L-valine/L-isoleucine

Table 28

Kansas, Manhattan #2 2001

Blends indicate the ratio of the methyl esters of L-valine/L-isoleucine

The species that was taken in the greatest number (20,480), in the greatest number of sites (33), and in the greatest number of site-years (54) wasP. anxia. This is not surprising given that, as was indicated previously, it is the most widespread species ofPhyllophaga in North America. Luginbill and Painter (1953) list it as occurring in every state in the United States except Arizona, California, Florida, Nevada, West Virginia, and Wyoming. They also report P. anxia from all ten Canadian provinces. Woodruff and Beck (1989) have subsequently reported it from Florida. W. B. Warner (personal communication) has examined a specimen of P. anxia from California and has reports ofP. anxia in Arizona.

Males of ten other Phyllophaga species were also captured in numbers >1000. These include P. futilis, P. congrua, P. crassissima, P. praetermissa, P. gracilis, P. hirtiventris, P. ephilida, P. rubiginosa, P. rugosa, and P. fusca. Males of 13 species were captured in numbers >100 but <1000 and males of 15 species were captured in numbers >10 but <100 (Tables 3a and 3b). Eighteen species ofPhyllophaga were recorded at ≥5 locations and 8 species were recorded at ≥11 locations (Tables 4a and 4b).

Geographical distributions and range extensions

Geographical distribution maps of Phyllophaga species captured during this study are found in Figures 3–63, arranged alphabetically by species. Shaded areas in these figures indicate the geographical ranges conveyed by Luginbill and Painter (1953) or Woodruff and Beck (1989) [P. (Phytalus)georgiana and P. (Phytalus)obsoleta only].

Figure 3

Figure 63

Most captures of Phyllophaga species recorded during this study were found within the geographical species distributions reported by Luginbill and Painter (1953). There are, however, several range extensions to report. The following species were found in locations in addition to those reported by Luginbill and Painter:P. curialis (Figure 14), P. drakei (Figure 17), P. forbesi (Figure 20), P. foxii (Figure 22),P. futilis (Figure 25), P. gracilis (Figure 29), P. gracilis var.angulata (Figure 30), P. hirtiventris (Figure 33), P. longispina (Figure 40), P. lota (Figure 41),P. marginalis (Figure 43), P. (fraterna)mississippiensis (Figure 46), P. postrema (Figure 50), P. praetermissa (Figure 51), P. quercus (Figure 53), and P. taxodii (Figure 59). Riley (1988) had previously noted range extensions of P. forbesi, P. quercus, andP. taxodii into Louisiana.

Figure 14

Figure 17

Figure 20

Figure 22

Figure 25

Figure 29

Figure 30

Figure 33

Figure 40

Figure 41

Figure 43

Figure 46

Figure 50

Figure 51

Figure 53

Figure 59

Changes in population levels from year to year within sites

Numbers of beetles of a particular species changed dramatically from year to year at the same trapping location. For example, traps were maintained at the Auburn, Alabama site during the 1997, 1998, and 1999 seasons for approximately the same time period each year. The numbers of P. gracilis captured declined from 1123 in 1997, to 710 in 1998, and to 98 in 1999 (Tables 5, 6, 7). In Lexington, Kentucky, from 1999 to 2000, the numbers of each of the six species captured more than doubled (Tables 29, 30).

Table 5

Alabama, Auburn 1997

Blends indicate the ratio of the methyl esters of L-valine/L-isoleucine

Table 7

Alabama, Auburn 1999

Blends indicate the ratio of the methyl esters of L-valine/L-isoleucine

Table 29

Kentucky, Lexington 1999

Blends indicate the ratio of the methyl esters of L-valine/L-isoleucine

Table 30

Kentucky, Lexington 2000

Blends indicate the ratio of the methyl esters of L-valine/L-isoleucine

Factors affecting the size of the population include not only weather during the flight period, but soil moisture and tilth conditions suitable for oviposition, egg hatch, and growth of larvae during the previous year or years that it takes for development to adults. Quality and quantity of larval host plants, soil textural characteristics, and species’ preferences for soil types also factor into population size and distributions (Katovich et al. 1998). Changes in population size of other species at other trapping sites may be seen in Tables 5–97. Species captured at a particular site changed from year to year as well, indicating that multiyear studies will yield a more realistic picture of population sizes and species distributions than will a single year of captures.

Table 97

Wisconsin, Verona 2000

Blends indicate the ratio of the methyl esters of L-valine/L-isoleucine

Male captures with sex attractants

The most important finding of the present study was the demonstration of the extensive use of the methyl esters of L-valine and L-isoleucine as sex attractants in the mate recognition systems of the Phyllophaga. In 56 discrete locations across the US and Canada, during 94 observation periods (some locations were trapped for multiple years), 61 species ofPhyllophaga were captured. The overwhelming majority (58) of these species are found in the Phyllophaga (sensu stricto) subgenus. Since there are 147 species in this subgenus in America north of Mexico (Evans 2003; Smith and Evans 2005), 39% of the species in this group were captured in traps during the course of this study.

Male trap captures are graphically illustrated in Figures 64–126. The figures are arranged alphabetically byPhyllophaga species. Within each species figure, graphs are arranged alphabetically by state or province abbreviation. The graphs demonstrate three general patterns of species-specific male responses to a particular blend or group of blends. The three general patterns are displayed inFigure 127. First, some species, such as P. vehemens, flew primarily to the 100/0 L-valine methyl ester/L-isoleucine methyl ester lure and were sensitive to increasing amounts of L-isoleucine methyl ester in the other blends, its presence significantly reducing captures1. P. congrua, however, had a broader response profile and was captured not only with the 100 % L-valine methyl ester lure, but also with blends containing 10%–20% L-isoleucine methyl ester (Figure 71). A similar situation was seen in responses of male P. hirtiventris (Figure 96). The second case (Figure 127) involved species such as P. forbesi that were captured primarily with the 100% L-isoleucine methyl ester lure. Increasing titers of L-valine methyl ester resulted in reduced or no captures2. In the third case (Figure 127), some species ofPhyllophaga, such as P. glabricula, required the presence of both compounds before captures occurred3. An examination of these male- response curves reveals that, whereas certain species had a rather broad response range to the L-valine methyl ester/L-isoleucine methyl ester blends,4 others exhibited response curves occupying a narrower range of blends5.

Figure 64

Figure 126

Figure 127

Figure 71

Figure 96

Specificity of response over time and space

A striking aspect of the intra-specific male flight responses to the sex attractants was their consistency between years and across geographic locations. Several species were recorded at only one site, but were captured at that site for two consecutive years6. The response profiles for each species in both years at those sites were nearly identical.

The majority of Phyllophaga species were recorded at more than one site (Tables 4a and 4b). As with the across-years comparison above, the intra-specific male-response curves from different geographic locations are similar as well. For instance, only five specimens ofP. balia were captured during this study, but they were captured at three different locations (Figure 6) and all with the 100% L-isoleucine methyl ester lure (Figure 68). Nearly 7000 P. congrua were captured at eight different sites (Figure 9) and all sites exhibited similar response curves (Figure 71). Comparable results are seen when other species are examined7.

Figure 6

Figure 68

Figure 9

Some species were captured at only one location and only during a single year, but multiple catches over time in the same or nearby blends furnish a series of independent observations that support responses to a particular lure despite the small numbers. For instance, six specimens of P. davisi Langston were captured in Marion Junction, Alabama in 1999, all in traps baited with the 100% L-isoleucine methyl ester lure (Figure 77) on six different dates between 4/5 and 4/28. P. davisi is a species that Luginbill and Painter (1953) indicate is rare, with “Only a few specimens seen.”

Figure 77

In Auburn, AL in 1998 two specimens of P. diffinis (Blanchard) were captured with the 100% L-valine methyl ester lure (Figure 78) - one taken on 4/16 and one taken on 4/21.

Figure 78

Another uncommon species, P. (Phytalus)georgiana Horn, was captured in Tifton, Georgia, in 2000. Two individuals of this species flew to the 100% L-valine methyl ester lure (Figure 89), one on 7/17 and one on 7/21. Woodruff and Beck (1989) report that no adult host plants are recorded, the larva is undescribed, and the life cycle is unknown. This species is one of seven North American species in the subgenus Phytalus. Members of this subgenus can be discriminated from the Phyllophaga (sensu stricto) by their cleft tarsal claws.

Figure 89

P. mariana is reported as a very rare species (Luginbill and Painter 1953). Four specimens were captured in Tifton, Georgia, in 2000 and 2001, on four different dates, in traps baited with the 90/10 or 80/20 L-valine methyl ester/L-isoleucine methyl ester blends (Figure 107).

Figure 107

Two specimens of P. taxodii Langston were captured in Louisiana in 1997 in the 35/65 L-valine methyl ester/L-isoleucine methyl ester blend (Figure 122), one on 7/3 and the other on 8/15. Luginbill and Painter (1953) list this species as uncommon, having been captured only in AL and MS. However, Riley (1988) reports that this species is not frequently taken at lights and that fair numbers have been captured in flight-intercept traps 50 feet above the ground in cypress stands. Riley concludes that a lack of light trap catches gives the impression of rarity but that the method of collection may be more important.

Figure 122

Similarly, R. J. Bauernfiend in Manhattan, Kansas indicated that in many years of light trapping he had never captured P. sylvatica, and was surprised to capture 104 individuals of this species during two years of sex attractant trapping (Figure 121).

Figure 121

Of some interest is the capture of both P.gracilis andP.gracilis variety angulata in traps baited with 100% L-isoleucine methyl ester (Figures 92 and 93). Woodruff and Beck (1989) indicate that “The exact status of this form (angulata) awaits further study”. The different forms of the male genitalia easily separate these populations ofP. gracilis. Photos of the two genitalic forms can be seen in Luginbill and Painter (1953). The two forms are sympatric over a large range (Figures 29 and 30). Langston (1927) provides illustrations of the genitalia indicating what appears to be a form intermediate between P. gracilis and P. gracilis varietyangulata.

Figure 92

Figure 93

Intra-location species interactions

The location tables (Tables 5–97) list the blends presented at each site in a particular trapping year and the numbers of Phyllophaga captured with each blend. At each site, the listed species are, by definition, sympatric. At some sites, sympatric species displayed asynchronous flight patterns, including species captured days, weeks, or in some cases, months apart. At other sites, different species ofPhyllophaga were synchronic as well as sympatric, but may or may not have been captured with the same sex attractant blends. The distinction of whether males of different species were or were not captured in the same blends is important because it can aid in identifying locations where inter-specific competition for pheromonal space may be occurring. Congeneric males flying to the same sex attractant blends indicate situations where there is potential for inter-specific mating interactions that afford opportunities for investigation into reproductive isolation involving additional species-specific sex attractant compounds, close-range mating behavior, and/or mating at different times.

Each of the three scenarios (1. sympatric and synchronically flying species captured using different blends; 2. sympatric and asynchronically flying species captured using the same blend; 3. sympatric and synchronically flying species captured using the same blend) were encountered in the course of this study, individually as well as in combination at different study sites. The following examples illustrate the three scenarios.

Figure 128

Figure 129

Figure 130

From the male capture data at the various trapping sites, many examples of different species flying synchronically, sympatrically, and to the same blends or blend groupings have been documented. However, nothing is known about whether these species fly at different times of the night or how close-range courtship behaviors are involved in mate recognition. Figures 131–133 display detailed information relating male response specificity curves and time of flight from three sites that demonstrate the complexity of interactions that can occur over a season. Figure 131 (KS Manhattan #2, 2001), demonstrates that P. inversa andP. vehemens flew synchronically to the 100% L-valine methyl ester lure. Similarly, there is potential for interaction between P. rubiginosa and P. sylvatica (middle L-valine methyl ester/L-isoleucine methyl ester blends), P. crassissima and P. fusca (lower L-valine methyl ester/L-isoleucine methyl ester blends), and P. futilis andP. bipartitia (100% L-isoleucine methyl ester lure). In the July and August flights at the same site, P. glabricula, P. affabilis, and P. ephilida were captured synchronically, but with different blends. Figure 132 (KY Lexington, 2000) shows that P. futilis and P. hirticula flew synchronically to the 100% L-isoleucine methyl ester lure, whereasP. ephilida was captured with the same lure, but later in the season. In Figure 133 (MA Amherst, 1999), synchronic species P. forsteri, P. fraterna, and P. fusca displayed overlapping male response curves to L-valine methyl ester/L-isoleucine methyl ester mixes, whereas P. anxia, P. longispina, andP. drakei also flew synchronically to the 100% L-isoleucine methyl ester lure.

Figure 131

Figure 133

Figure 132

Table 98 outlines, in a briefer format, other trapping locations and the species involved where inter-specific attraction might occur as a result of competition for pheromonal space. However, the possibility of interactions postulated by the overlap of the male response curves in time and space may not necessarily reflect the reality in the field in that females may or may not have a narrower range of sex pheromone blend production than is suggested by what the males are capable of responding to. The potential for inter-specific interactions might be predicted with greater accuracy by combining analysis of blend ratios produced by a number of individual females with knowledge of male captures by various blends and determining if male response curves overlap congeneric female production curves.

Table 98a

Synchronic species captured by the same or nearby sex attractant blends, by state.

Interspecific copulation between Phyllophaga species has been reported in the literature. Fattig (1944) reports (p. 26) that he collected a male P. hirticula copulating with a female P. anxia. Referencing the data from the present study, P. hirticula males were captured in traps baited with the 100% L-isoleucine methyl ester lure (Figure 95).P. anxia males of both the northern and the southern genitalic form were also captured in traps baited with the 100% L-isoleucine methyl ester lure (Figures 66a, 66b, 66c, 66d, 66e and 67). It is likely that the male P. hirticula flew upwind following an L-isoleucine methyl ester plume to find not a conspecific female P. hirticula, but a congeneric female P. anxia. P. hirticula and P. anxia males possess genitalia whose cuticular structures are exceedingly different (see images in Woodruff and Beck, 1989). Their soft sac structures are very different as well (P.S. Robbins, personal observation). Their vestitures also differ, P. anxia being glabrous and P. hirticula being hirsute. Although interspecific genitalic differences could and sometimes do play a role in reproductive isolation of some taxa (Eberhard 1985, Sota and Kubota 1998), genitalic differences clearly did not prevent copulation from taking place in this case.

Figure 95

Figure 66a

Figure 66b

Figure 66c

Figure 66d

Figure 66e

Figure 67

Copulation does not inevitably lead to fertilization or production of offspring (Eberhard 1996), and similarly, attraction to a congeneric Phyllophaga female does not inevitably lead to copulation. In a study from Costa Rica, Eberhard (1993), reporting on the copulatory behavior of several species of Phyllophaga, states of P. vicina, that “Early in the evening solitary females rested immobile and apparently emitted an attractant, as males arrived in flight from downwind. The pheromone apparently also attracted males of P. valeriana, as on three occasions I saw one or more males of this species hover near a female P. vicina (beetles were captured to verify their species identity). One P. valeriana male landed on the female, then immediately took flight and left, suggesting that a second cue, possibly on the beetle’s surface, was used to distinguish species identity. Contact pheromones may be used in the melolonthine genus Macrodactylus (Eberhard 1992).” These observations indicate that more studies are needed to clarify the role of morphology and/or contact pheromones in close-range mate recognition in Phyllophaga. Eberhard (1993) reports that “secondary sexual modifications of the sculpturing of the front legs, the ventral bristles, and the overall leg length of maleMacrodactylus may function as courtship devices prior to and during copulation”. Although the Phyllophaga are renowned for their extravagant and often asymmetric genitalic morphology, male hind tibial spurs also often assume unique configurations that provide excellent taxonomic characters for species assignments (Luginbill and Painter 1953; Woodruff and Beck 1989; Woodruff and Sanderson 2004). The role tibial spurs play in close-range mate recognition or copulatory courtship in the Phyllophaga is unclear. Males of somePhyllophaga species also have extensive ventral bristles or possess unique morphological characters on the venter, similar toMacrodactylus (P.S. Robbins, personal observation).

Intraspecific variation in male response: P. anxia

The consistency of intra-specific male responses over space and time that was discussed earlier contrasts with the extensive variation noted in the male-response curves of P. anxia to the various blends of L-valine methyl ester/L-isoleucine methyl ester sex attractants (Figures 66a, 66b, 66c, 66d, and 66e). The variations demonstrated in the male-response profiles ofP. anxia are of four general forms:

Figure 134

Figure 135

Figure 136

Figure 137

All the P. anxia males from Figures 134 to 137, as well as all other P. anxia males in Figures 66a, 66b, 66c, 66d, and 66e are of the northern genitalic form (Luginbill and Painter 1953;Woodruff and Beck 1989). Male P. anxia of the southern genitalic form (Luginbill and Painter 1953;Woodruff and Beck 1989) were captured exclusively with L-isoleucine methyl ester alone (Figure 67). They were captured in both a smaller number of locations (8 vs.25) and in much smaller numbers (20 vs. 20,640) (Table 2a) thanP. anxia males of the northern genitalic form. Unpublished data from studies conducted at the Franklinville, NY, site suggest that L-isoleucine methyl ester responding P. anxia males (both northern and southern genitalic forms) are more sensitive to the presence of L-valine methyl ester than are L-valine methyl ester responding males to the presence of L-isoleucine methyl ester. Male captures in the L-isoleucine methyl ester-baited traps may have been suppressed by the presence of the L-valine methyl ester at the trap sites.

The manner in which the different forms of the P. anxia male sex pheromone response profiles are distributed across North America reveals important information. The five locations yielding response profiles (10 site-years) from P. anxia males that were captured in blends of both L-valine methyl ester and L-isoleucine methyl ester are found only in southeast Massachusetts and Rhode Island (see Figures 66a, 66b, 66c, 66d, and 66e including all the MA Carver, MA Lakeville, MA Plympton #1, MA Plympton #2 and RI Kingston sites). Surrounding these five locations are trapping sites to the west (as far west as Wisconsin) and to the north (as far north as the provinces of Nova Scotia and Ontario) that represent those populations of P. anxia males that responded to only L-valine methyl ester or to only L-isoleucine methyl ester, but did not require a blend of the two for capture (Figure 138). The male response curves generated by the beetle captures at those trapping sites yield a distribution map that is patchy in terms of unequal distributions of the two populations. Some sites harbor only one of the two populations, while other sites hold both, thus generating a bimodal distribution curve.

Figure 138

A detailed examination (including the soft sacs) of male individuals of the L-valine methyl ester responding populations, the L-isoleucine methyl ester responding populations, and the blend responding populations of P. anxia revealed no character that could be used to differentiate the populations. Further work is planned that will use DNA sequence data from both mitochondrial and nuclear genes to generate gene genealogies with which to document genetic relationships within and among the three races across the US. Microsatellite markers will also be used to characterize allele frequencies in natural populations and consequently estimate the extent of gene exchange among different pheromone races where they occur together and between geographically isolated populations of single pheromone races.

Intra-specific variation in male response: P. fraterna

A second instance of intra-specific variation in male response to blends presented was noted at the State College, Pennsylvania, trapping site in 1999 and 2000. Male individuals of a species determined as P. fraterna were captured by two blend groupings in both years (Tables 80 and 81 and Figures 85 a, 85b, and 86). In 1999, 18 males were captured with the 0/100 L-valine methyl ester/L-isoleucine methyl ester blend, whereas 13 males were captured with the L-valine methyl ester/L-isoleucine methyl ester mixtures. In 2000, 19 males were captured with the 0/100 L-valine methyl ester/L-isoleucine methyl ester blend whereas 5 males were captured with the L-valine methyl ester/L-isoleucine methyl ester mixtures. Phyllophaga fraterna from locations other than Pennsylvania were captured exclusively in the blends of L-valine methyl ester/L-isoleucine methyl ester (Figures 85a and 85b).

Table 80

Pennsylvania, State College 1999

Blends indicate the ratio of the methyl esters of L-valine/L-isoleucine

Table 81

Pennsylvania, State College 2000

Blends indicate the ratio of the methyl esters of L-valine/L-isoleucine

Figure 85a

Figure 85b

Figure 86