Conotrachelus, Dejean, 1835

Torres, Betzabeth Cecilia Pérez, Skuhrovec, Jiří, Marín-Cevada, Vianey & Elizalde-González, María P., 2018, Conotrachelus dimidiatus Champion, 1904 (Coleoptera: Curculionidae: Molytinae): morphological re-description of the immature stages, keys, tribal comparisons and biology, Zootaxa 4433 (1), pp. 127-140 : 135-136

Keys to the immature stages of some Conotrachelus species

Larvae (last instar). The following key is based on the larvae of Conotrachelus dimidiatus described in this paper and on seven selected descriptions of larvae in the genus Conotrachelus published previously ( Brooks & Cotton 1924; Gibson 1965; Blair et al. 1980; Valente & Gorayeb 1994).

1. Endocranial line reaches beyond two-thirds the length of frons.................................................. 2

- Endocranial line does not reach behind two-thirds the length of frons, does not reach more than half the length........... 6

2. Des1 of epicranium minute or absent........................................................... C. anaglypticus

- Des1 of epicranium distinctly long......................................................................... 3

3. Postmentum strongly sclerotized (see Figure 5 in Gibson 1965)............................................ C. naso

- Postmentum usually not sclerotized, appearing white......................................................... 4

4. Pronotum with only two long prns, the anterior seta more than twice as long as the posterior one............... C. retentus

- Pronotum with only three long prns, all setae the same length................................................... 5

5. Epipharnyx with two ams ...................................................................... C. dimidiatus

- Epipharnyx with only one ams .................................................................. C. imbecillus

6. Endocranial line not reaching half the length of frons, only one-third the length........................... C. posticatus

- Endocranial line reaching half the length of frons............................................................ 7

7. Des1 and des2 of epicranium equal in length, both very short............................................. C. carinifer

- Des1 and des2 of epicranium of different lengths, des1 minute or very short, but des2 long..................... C. nenuphar

Pupae. The following key is based on the pupae of C. dimidiatus described in this paper and on six descriptions of pupae of the genus Conotrachelus published previously ( Brooks & Cotton 1924; Gibson 1965; Valente & Gorayeb 1994).

1. Profemoral teeth present................................................................................. 2 - Profemoral teeth absent................................................................................. 5

2. Pronotum with only five setae on each side........................................................ C. dimidiatus

- Pronotum with eight or more setae on each side.............................................................. 3

3. Setae around eyes (vs, os, and sos) short. Pronotum with eight setae on each side............................... C. naso

- Setae around eyes (vs, os, and sos) very long. Pronotum with nine setae on each side................................ 4

4. Body length 5.0– 5.5 mm .................................................................... C. anaglypticus

- Body length 6.5–8.0 mm....................................................................... C. nenuphar

5. Urogomphi thick............................................................................ C. imbecillus

- Urogomphi thin....................................................................................... 6

6. Interocular pit deep and well formed; base of rostrum with a median longitudinal groove; body length 6.5–8.0 mm C. carnifer

- Interocular pit absent or poorly formed; base of rostrum with a shallow median longitudinal groove; body length 4.5–6.5 mm ........................................................................................... C. posticatus

Measurements of larval instars in Conotrachelus species. Muñiz-Vélez & González (1982) listed that larvae of C. dimidiatus have five instars. In contrast to this information, Valente & Gorayeb (1994) and Bailez et al. (2003) indicated four instars for C. imbecillus and C. psidii , respectively. Despite measuring fewer head capsules (n = 10), we were able to calculate the hypothetical cephalic width according to Dyar’s law, using the ratios 1.35, 1.40 and 1.50 ( Rowe & Kok 1985; Sprick & Gosik 2014), because we used larvae from different stages of the life cycle and their head width varied to a large extent. The best approximation to the real size was obtained for 5 instars, and a head capsule width of 0.6 for instar 1 when using a factor of 1.35, yielding R = 0.987. For the larvae of C. dimidiatus maintained in laboratories in Morelos and Puebla ( Mexico), no differences were found, and the average cephalic width was 1.69 and 1.65 mm, respectively, for the fifth instar. The increase in size observed in Fig. 4 was almost identical to that reported by Muñiz-Vélez & González (1982), and we also confirmed their extensive studies in a theoretical way.

In both investigations on the larval stage of C. psidii ( Bailez et al. 2003; Monroy & Insuasty 2006), which were conducted in Brazil and Colombia, respectively, four instars were identified. The cephalic capsule of the larvae of C. dimidiatus is approximately 0.16 mm larger in the fourth instar than C. psidii and is, in general, approximately 0.50 mm larger in the fifth instar than the biggest capsule of C. psidii ( Bailez et al. 2003) .

Figures

FIGURE 4. Head capsule width of Conotrachelus dimidiatus in different larval instars (n = 10).