Euseius gallicus Kreiter and Tixier, 2010

Tixier, M. - S., Kreiter, S., Okassa, M. & Cheval, B., 2010, A new species of the genus Euseius Wainstein (Acari: Phytoseiidae) from France, Journal of Natural History 44 (3 - 4), pp. 241-254 : 242-252

Euseius gallicus Kreiter and Tixier sp. nov.

( Figures 1–8 )

Holotype

Female , on P. cerasus L., Montpellier, France, June 2007, deposited at Montpellier SupAgro/ INRA Acarology Laboratory Collection.

Allotype

Male , on P. cerasus L., Montpellier, France, June 2007, deposited at Montpellier SupAgro/ INRA Acarology Laboratory Collection.

Paratypes

Twenty-five females (on 25 preparations) collected on V. tinus, Montpellier , France ; 30 females (on 30 preparations) collected on T. platyphyllos, Montpellier , France ; 29 females (on 29 preparations) collected on P. cerasus, Montpellier , France ; 31 females (on 31 preparations) collected on A. hippocastanum, Montpellier , France ; June 2007; one male collected on P. cerasus, Montpellier , France , June 2007; deposited at Montpellier SupAgro / INRA Acarology Laboratory Collection, collector: Mireille Okassa.

Other material

Fourteen females collected on Vitis vinifera, Montmartre, Paris , July 2003, deposited at Montpellier SupAgro/INRA Acarology Laboratory Collection, collector: Serge Kreiter.

Etymology

The name of the species refers to the country where the species was collected and commonly found.

Description – adult female (n = 116)

Dorsum ( Figure 1 ). Dorsal shield 334 (259–369) long and 226 (179–252) wide, strongly reticulated on the whole dorsum, with seven solenostomes (gd1, 2, 4, 5, 6, 8 and 9), five pairs of poroids, 17 pairs of dorsal setae and two pairs of sublateral setae: j1 33 (22–40), j3 34 (23–42), j4 13 (8–20), j5 15 (9–20), j6 17 (11–22), J2 18 (11–24), J5 5 (3–8), z2 29 (20–37), z4 31 (21–40), z5 14 (8–19), Z1 17 (11–21), Z4 19 (13–25), Z5 54 (35–62), s4 41 (30–52), S2 22 (16–28), S4 22 (18–29), S5 28 (19–36), r3 15 (12–21), R1 15 (11–20). All setae smooth.

Peritreme ( Figure 1 ). Extending forward between bases of j3 and z2.

Venter ( Figure 2 ). Sternal shield slightly reticulated. Other shields smooth. Sternal shield large, with three pairs of setae and two pair of pores; one pair (st4) on the membrane; posterior margin not clearly outlined in all specimens, but distinct in the holotype. Distances between st1–st3 63 (56–73), st2–st2 65 (56–73), st5–st5 74 (62– 87). Two pairs of metapodal shields, primary shield 21 (16–25) long, 5 (3–9) wide and secondary shield 9 (8–10) long and very thin and clear for the smallest one. Ventrianal shield with three pairs of preanal setae, JV1, JV2 and ZV2 and one pair of large elliptical preanal pores. Membrane surrounding ventrianal shield with four pairs of setae ZV1, ZV3, JV4 and JV5 and five pairs of round to oblong poroids; ventrianal shield 98 (79–113) long, 50 (41–66) wide at level of anterior corners and 76 (61–87) wide at level of anus. JV5 40 (30–49) long and smooth.

Chelicera ( Figure 3 ). Fixed digit 25 (24–33) with five teeth and moveable digit 23 (20–25) with one tooth.

Spermatheca ( Figure 4 ). Calyx of spermatheca tubular ( Denmark et al. 1999), elongated vase-shaped, 7 (5–10) wide and 16 (11–21) long, with a small neck and an atrium at the basis, a visible ductus minor and a long ductus major.

Legs ( Figure 5 ). Legs IV with three smooth macrosetae, genual 38 (35–42), tibia 37 (35–50), basitarsus 58 (39–71). The macroseta on the basitarsus with a sharp hyaline tip. Chaetotactic formula of genu II: 1-2/0, 2/0-1; genu III: 1-2/0, 2/0-1. Length of leg I: 255–285, II: 225–258, III: 217–250, IV: 265–313.

Description – adult male (n = 2)

Dorsum ( Figure 6 ). Dorsal shield as in the female but much less reticulated, 228–238 long and 140–150 wide. Setae j1 13–15, j3 18, j4 13–15, j5 13–15, j6 15–18, J2 20–25, J5 10–12, z2 13–20, z4 15–18, z5 13–15, Z1 20–25, Z4 45–50, Z5 43–55, s4 18 –25, S2 23 –33, S4 20 –23, S5 18 –20, r3 15–20, R1 18–20.

Peritreme ( Figure 7 ). Extending just past z4. Venter ( Figure 8 ). All shields slightly reticulated. Sternogenital shield with five pairs of setae and two pairs of pores. Distances between st1–st3 55, st2–st2 55–58, st5–st5 60 – 68. Ventrianal shield not fused with peritremal shields with three pairs of preanal setae, JV1, JV2 and ZV2, one pair of large elliptical preanal pores and two pairs of poroids. Membrane surrounding ventrianal shield with one pair of setae JV5 at level with anal opening, and no oblong poroids; ventrianal shield 88 long, 108–120 wide at level of anterior corners and 53–63 at level of anus.

Legs. Three macrosetae on leg IV, genual 25–28, tibia 20, basitarsus 33–35. Chaetotactic formula of genu II and genu III are identical to the female. Length of leg I: 228–238, leg II: 200–213, leg III: 200–203, leg IV: 233–255.

Chelicera ( Figure 8 ). Spermatodactyl with an elongate toe terminating in the foot, shaft 15 long.

Diagnosis

As only three species of Euseius are reported from the west part of the west Palaearctic region, the specimens of E. gallicus sp. nov. were at first compared to these three species. They clearly differ from E. finlandicus and E. scutalis , in several characters, such as the shape of the spermatheca, the lengths of both peritreme and of some dorsal setae ( Ferragut and Escudero 1997). Euseius gallicus sp. nov. is more difficult to differentiate from E. stipulatus . Both molecular and morphological analyses showed that these two species are valid and differ by the terminal shape of the calyx of the spermatheca, the dorsal shield reticulation (the dorsal shield of E. gallicus sp. nov. is more reticulated than the dorsum of E. stipulatus ) and lengths of the seta z2 and ventrianal shield ( Okassa et al. 2009). According to the 187 species of Euseius , four seemed to be morphologically close to Euseius gallicus sp. nov.: Euseius querci (Liang and Ke) , Euseius longiverticalis (Liang and Ke) , Euseius amissibilis Meshkov and Euseius kirghisicus (Kolodochka) . However, it was impossible to contact the authors of these species for a loan of type specimens, except for Dr Kolodochka (Institute of Zoology of National Academy of Sciences of Ukraine, Kiev). As he could not send the type of E. kirghisicus for postal security reasons, specimens of Euseius sp. were sent to him for confirmation.

Euseius amissibilis ( Meshkov 1991) was described from Tajikistan, on Platanus orientalis L.. It differs from E. gallicus sp. nov. by the lengths of setae Z1, JV5 and to a lesser extent j1, j3, S5 and StIV ( Table 1). The lengths of JV5 and S5 are longer in E. gallicus sp. nov. than in E. amissibilis , while Z1 is shorter in E. gallicus sp. nov. The fixed digit of E. amissibilis has two teeth instead of five as in E. gallicus sp. nov. However, on the drawings of the original description, E. amissibilis seems to have more than two teeth on the fixed digit and perhaps more than five. Moreover, the fixed digit is not currently used as a valid character from a systematic point of view because it is usually very difficult to count the teeth.

However, Dr Kolodochka compared specimens of E. gallicus sp. nov. with E. amissibilis and confirmed that they are two separate species essentially because of the differences in seta lengths. Nevertheless, according to what is known on dorsal seta length intraspecific variation ( Tixier et al. 2008) and to similarities between the two species, some doubts could remain.

Euseius querci (Liang and Ke 1983) was described from China on Quercus acutissima Carruthers. The dorsal setae of E. querci and E. gallicus sp. nov. are subequal to equal in length ( Table 1). However, in E. gallicus sp. nov., the peritreme reaches to a level between z2 and z4 compared with a level between j3 and z 2 in E. querci .

Euseius kirghisicus (Kolodochka 1979) was described from Kyrgyzstan, on Prunus sp. It differs from E. gallicus in the lengths of the seta S5 (longer than in E. kirghisicus ) ( Table 1). Furthermore, the dorsal shield of E. kirghisicus is not reticulated and the calyx of the spermatheca is narrower than that of E. gallicus sp. nov. Dr Kolodochka also compared specimens of E. gallicus sp. nov. with specimens of E. kirghisicus and found them to be separate species.

Euseius longiverticalis (Liang and Ke 1983) was also described from China, on an unknown plant and is related to E. gallicus sp. nov. ( Table 1). All attempts to obtain the type specimens of E. longiverticalis were unsuccessful. Therefore, we had to rely only on the original description of E. longiverticalis . In both species the dorsal setal lengths are equal ( Table 1), the dorsal shields are reticulated and the peritremes reach to a level between j3 and z2. The spermatheca of E. longiverticalis is not clearly depicted. Apparently the only difference between these two species is the number of teeth on the fixed cheliceral digit, namely four in E. longiverticalis and five in E. gallicus sp. nov. Again, even if the dentition of the chelicerae of the Phytoseiidae is considered an important character to distinguish between species ( Chant and McMurtry 2007; Tixier et al. 2008), the fixed digit dentition has not been considered as an important character from a systematic point of view. Therefore, we have to be cautious. Euseius longiverticalis was never reported again after its description, whereas E. gallicus sp. nov. was frequently encountered in France [Montpellier on several trees, Paris on Vitis vinifera and on large-leaved summer linden T. platyphyllos, Calas (Bouche-du-Rhône, France) on the wild rose Rosa canina L. and the box elder Acer negundo L.].

In conclusion, this paper shows the necessity of very good descriptions to assess the new species state of specimens and the difficulty of retrieving type species for comparisons. To determine the differences between these species and especially between E. amissibilis , E. longiverticalis and E. gallicus sp. nov., molecular techniques would be useful; however, for this, alcohol-preserved or live specimens would be required.

Figures

Figure 1. Dorsal shield of the female of Euseius gallicus sp. nov. (from the holotype).

Figure 2. Ventral shields of the female of Euseius gallicus sp. nov. (from the holotype).

Figure 3. Chelicera of the female of Euseius gallicus sp. nov. (from the holotype).

Figure 4. Calyx of spermatheca of the female of Euseius gallicus sp. nov. (from the holotype).

Figure 5. Macrosetae of leg IV of the female of Euseius gallicus sp. nov. (from the holotype).

Figure 6. Dorsal shield of the male of Euseius gallicus sp. nov. (from the allotype).

Figure 7. Ventral shields of the male of Euseius gallicus sp. nov. (from the allotype).

Figure 8. Chelicera of the male of Euseius gallicus sp. nov. (from the allotype).