Laemosaccus nephele, (Herbst)

Hespenheide, Henry A., 2019, A Review of the Genus Laemosaccus Schönherr, 1826 (Coleoptera: Curculionidae: Mesoptiliinae) from Baja California and America North of Mexico: Diversity and Mimicry, The Coleopterists Bulletin (MIMICRY AND LAEMOSACCUS In an earlier paper (Hespenheide 1996), I presented the hypothesis that species of Laemosaccus of the L. nephele group with red humeral spots on the elytra were Batesian mimics of members of the Chrysomelidae in the subfamily Clytrinae. There is no evidence that Laemosaccus species are distasteful, and what is either L. nephele and / or L. obrieni have been reported as prey items of birds (Beal 1912). In Cave Creek Canyon, Cochise County, Arizona, 21 forms (species and “ subspecies ”) of Clytrinae were hypothesized to be the primary models of 22 species of mimics in the families Anthribidae (one species), Bruchidae (two species), Buprestidae (four species), Chrysomelidae, subfamily Cryptocephalinae (three species), Coccinellidae (six species), Curculionidae, subfamily Baridinae (one species), and Laemosaccus (five species). Of these, the coccinellids and the cryptocephaline chrysomelids are probably distasteful Mullerian co-mimics. Ecologically, the species of Laemosaccus co-occurred with their clytrine models on both desert legumes and canyon oaks, although more clytrine species occurred in the desert and more Laemosaccus species occurred in the canyons. Species of clytrines showing the mimetic pattern are common throughout Mexico (Bellamy 2003, who renamed the Mexican buprestid genus Acherusia Laporte and Gory, 1837 as Mimicoclytrina Bellamy to reflect their resemblance to clytrines), but decline in numbers of species and in the proportion of the clytrine fauna through Central America to Panama (Hespenheide 1996, fig. 2). Laemosaccus seems to follow a similar pattern. Mimicry is more common in large faunas, especially in wet tropical areas (Hespenheide 1986, 1995); because the largest clytrine fauna is in Mexico, the clytrine mimicry complex is also larger there (Hespenheide 1996). This complex has more members than I first enumerated and deserves further study. The evolution of mimicry produces resemblances between unrelated species (Laemosaccus and other putative mimics, with clytrines and perhaps other Chrysomelidae and Coccinellidae as models; see Hespenheide 1976, 1996) and selects against the divergence of related species. In Batesian mimicry - hypothesized to be the form of relationship between Laemosaccus and clytrines - the selection for precision of mimicry is stronger on the mimic (Laemosaccus), so that resemblances among them should be closer, regardless of ancestry. Close morphological resemblances based on ecology rather than ancestry may be termed mimetic homoplasy (Hespenheide 2005) and can make recognition of species difficult (as in Laemosaccus) or complicate phylogenetic analyses. I have speculated (Hespenheide 1996) that the sympatric “ subspecies ” of the clytrine models (Moldenke 1970) may in fact be reproductively isolated sibling species. It will be interesting to see whether or not genomic studies show the closeness of relationships among Laemosaccus species that the morphology suggests) 73 (4), pp. 905-939 : 906-907

The L. nephele group

Of the 11 species in the L. nephele group that occur in the USA, nine are entirely southwestern and a 10 th occurs there; eight of them also occur in Mexico. Of the nine, seven are associated with oaks as adults, and the other two were reared from mesquite and other legumes. Geographically, Arizona has the richest fauna, with seven species. Texas has five species, including the primarily eastern L. nephele . Three southwestern locations have been relatively well collected: in southeastern Arizona, Madera Canyon in the Santa Rita Mountains and Cave Creek Canyon in the Chiricahua Mountains; in Texas, the Davis Mountains. The larger number in the Chiricahua Mountains is probably an artifact of less intensive collecting elsewhere. All of the new species from Arizona and one from Texas are found in the Madrean Archipelago “sky islands” along the Mexican border (en.wikipedia.org/wiki/Madrean_ Sky_Islands); all but two of them have also been collected in Mexico, but these two can be expected to occur in Mexico.

Champion (1903) noted that in Mexico and Central America L. nephele (Champion’ s “ L. plagiatus ”) was “not uncommon...varying much in size...and in the extent of the rufous or ferruginous humeral patch...[and]...sculpture of the prothorax.” He concluded that “The various forms occur in the same localities, and they cannot be separated.” They can be separated, but not always easily. Of the 11 species in the USA, eight have also been collected in Mexico, but not L. nephele . There are numbers of additional species that have not been collected north of Mexico, and I have seen Laemosaccus specimens with red posthumeral patches from as far south as western Panama, although not commonly south of Honduras. Perhaps because many Laemosaccus are associated with oaks, the separation of all of the Mexican and Central American species may be a very difficult task if this genus is as complex as the leaf-mining genera of beetles I have studied that use oaks as larval hosts ( Curculionidae : Tachygonus Schönherr ( Hespenheide 1992) ; Buprestidae , Brachys Dejean ( Hespenheide 2015 and unpublished data)).

Diagnostic Characters of the Laemosaccus nephele Group

Although species of the L. nephele group resemble each other closely, the resemblance is superficial and differences are subtle, as is often true in mimicry complexes (see discussion below). In addition to size, the following characters vary in consistent ways among species:

Coloration. Although the basic pattern is black with red humeral spots, the size, shape, and placement of the spots varies within and among species.

Setation. Species of the L. nephele group tend to be more or less densely setose ventrally glabrous or inconspicuously setose dorsally, but there are subtle differences. Some species have the base of the rostrum or the anterior margin of the pronotum setose, whereas those in the L. texanus group are nearly glabrous throughout. A postscutellar spot of setae may occur in species throughout the genus. The pygidium and propygidium (see below) may have distinctive kinds and patterns of setae.

Sculpture. The sculpture of the pronotum varies from finely to coarsely punctate to rugose among species, and the punctures may be confluent. Elytral intervals 3 and 5 are distinctly toothed in some species. The sculpture of the rostrum separates species and sexes. The profemora have a tooth, which differs in size among species.

Male Genitalia. The aedeagus is usually distinctive among species. Species differ in the nature of the aedeagal apex (obtuse, acute, or truncate), lateral profile (straight or arcuate and/or apically deflexed), and presence or absence of dark internal structures. In addition, the shape of the parameres ( Lyal 2014; dorsal processes of the tegminal ring in Thompson 1988; or epimeres of the phallobase in Burke 1959) differs among species.

Sexual Dimorphism. Male Laemosaccus have been characterized as having the pygidium transversely “divided” into a dorsal “propygidium” ( Champion 1903) and a ventral pygidium; females have an undivided pygidium. Laemosaccus species have the usual situation in weevils in which for females the pygidium is abdominal tergite 7, whereas in males the pygidium is not “divided,” rather, abdominal tergites 7 (“propygidium”) and 8 (“pygidium”) are both visible. Here I use tergite 7 and tergite 8 to avoid confusion and false homology. Laemosaccus is dimorphic in other secondary sexual characters. In males of some species, the metasternum and first two abdominal sternites are either more glabrous or more setose, or excavated, or emarginate on the posterior margin. Sexual dimorphism of the rostrum is usual: the male rostrum usually shorter, stouter, and more strongly sculptured with punctures or rugosity, whereas the female rostrum is often longer, narrower, and more or less polished, but species differ in the nature and extent of such differences.