Nigritothrips longistylosus Priesner

Nigritothrips longistylosus (Priesner)

Belothrips longistylosus Priesner, 1920: 53

Bhatti (1978) distinguished Nigritothrips from Belothrips by the following character states: antennal segments V and VI equally broad and unconstricted at their junction; microtrichia absent on antennal segments (or rudimentary), antennal segment IV with four setae (instead of the usual five). The two species of Nigritothrips are distinguished by the length of the sensoria on antennal segments V and VI, and the length of antennal segment VII (Bhatti 1978; zur Strassen 2003).

Macropterous male: Body dark brown (Fig. 1), including antennae and legs, fore tibiae and tarsi brownish yellow; fore wings brown. Antennal segment VII clearly shorter than segment VI, approximately 0.6 times as long as VI (Fig. 2); dorsal setae on III and IV 14–17 microns, on III these setae are as long as segment width. Sternites II–VIII each with large oval pore plate (Fig. 5).

Measurements (in microns). Body length 1550–1660 (Fig. 1). Antennal segments I–VIII length (Figs 2, 3): 20, 34, 46, 39, 32, 50, 21, 20. Head (Fig. 4): length 112, width 130; interocellar setae 6; postocellar setae 7. Pronotum (Fig. 6): length 105, width 185; marginal setae 7. Mesonotum (Fig. 7): Length 85, width 130, S1 7, S2 11. Metanotum (Fig. 7): length 60, width 65, anteromarginal setae 20, discal setae 11. Fore wing (Fig. 9) length 775; clavus with five setae. Leg I 335, II 315, III 430. Abdominal tergite V (Fig. 10): length 60–65; width 185–195; S 1 24 –37; lateral setae 14–26; tergite IX (Fig. 8): S1 40, S 2 25, S3 45.Sternites (Fig. 11): pore plate on VI length 50–52, width 115–120; marginal setae: 22–25.

Larvae. Internal pigment red (Fig. 14), color weaker in larva I (Figs 15, 16). Second instar larva with short mouth cone; pronotum without distinctive reticulate markings; antennal segments III and IV (Fig. 18) with five and seven rings of microtrichia rows on both dorsal and ventral surfaces; body setae with apex acute. Chaetotaxy of larva II: head (Fig. 21) with setae S1, S2, S3 and S4 acute at apex (S1 9, S2 11, S3 9 and S4 10). Pronotum (Fig. 17) (S1 14, S2 9, S3 11, S4 10, S5 10, S6 15). Meso and metanotum with acute setae. Abdominal tergites II–VIII with D1–D3 acute at apex. Tergite VII (Fig. 20) (S1 40, S2 45, S3 68); Tergite VIII (S1 39, S2 43, S3 47), Tergites IX (S1 29, S2 29). Tergites with ornamentation plates (Fig. 19). Tergite X with a thorn-like spines 21 microns long (Fig. 22).

Biology. Females and males were collected in flowers of Cruciata laevipes throughout May but they were not found in June. Larvae were recorded from the first week of May to the second week of June (Fig. 12). During 2011 and 2012 a total of nine females of the polyphagous species Thrips tabaci and four of Aeolothrips intermedius were also found. During June other species of Rubiaceae were sampled that were abundant in the area but bloom soon after C. laevipes, including Galium aparine and G. mollugo, but no N. longistylosus were found on these plants (Table 1). Presumably the pupae of N. longistylosus have a long overwintering period, unless there is another generation on some other host plant in late summer. During 2011 69 females and 9 males were captured, and in 2012 107 females and 13 males were collected. These data show a proportion of males to females of 0.12̶0.13. Adult females, but not males, of N. longistylosus were parasitized by larvae of Granjeanella multisetosa (Acari: Erythraeidae) (Zhang & Goldarazena, A 1996, Goldarazena & Zhang 1997). The index of parasitism was 5% in 2011 and 3% in 2012.

Cruciata laevipes is a Euro-Siberian plant that is known across Europe to Siberia (Fitter & Peat 1994). In the Iberian Peninsula it is present in the North where it grows in meadows, road verges, riverbanks, scrub and open woodland, generally on well-drained calcareous soils. In the Basque Country the species is known from wet meadows and grasslands, shaded forest environments (pine, fir, beech and oak) on soils rich in organic matter (Fig. 13). It blooms in spring (first of May to the end of June) (Castroviejo et al. 1986) and the flowers sometimes contain a diversity of thrips (Goldarazena & Mound 1997).

Nigritothrips zurstrasseni Bhatti was collected in Austria in a prairie formed with grasses (Bhatti 1978), but there is no precise information concerning the host plant. Collecting methods based on scattered and isolated sampling are not informative about the plants where the thrips put their eggs and can result in erroneous associations. Much effort is needed during sampling to discover the plant where a thrips completes its life cycle. Repetitive seasonal captures throughout the years, and presence of immature stages of the thrips on the same plant are essential to establish host correlations.