Sennertia alfkeni ( Oudemans 1900 )

Okabe, Kimiko, Shun, Makino, Ichi & Endo, Tomoji, 2008, Polymorphism in the deutonymph and adult of Sennertia alfkeni (Acari: Chaetodactylidae) associated with the large carpenter bee, Xylocopa appendiculata circumvolans (Hymenoptera: Apidae), Journal of Natural History 42 (19 - 20), pp. 1361-1384 : 1366-1377

Sennertia alfkeni ( Oudemans 1900)

Trichotarsus alfkeni Oudemans, 1900:115 , Sennertia alfkeni Zakhvatkin, 1941:533– 535 , Sennertia alfkeni Fain, 1974:229, 1981:163 , Trichotarsus japonicus Oudemans, 1900:117 , Sennertia japonicus Fain, 1974:224, 1981:163

Larva ( Figures 5A,B )

Body ovoid, length 213.5 (190.0–227.5), width 137.0 (120.0–150.0), N 510.

Gnathosoma . Structures similar to those in female. Chelicera stout, chelate; fixed digit with two blunt teeth apically and three smaller teeth basally; movable digit with three large teeth basally. Cheliceral seta short, stout, positioned paraxially ventral to cheliceral spur. Rutella deeply divided, with untoothed lateral lobes longer than median lobes. Palps two segmented; basal segment with one dorsal and one ventral filiform seta; distal segment with one filiform seta and very short distal solenidion.

Idiosomal venter. Cuticle striate, striae smooth medially, less distinctive than dorsal striae. Coxal apodemes I fused in a Y-shape; apodemes II–III ending freely; coxal fields I and III each with a pair of filiform seta (1a, 3a); a pair of short sejugal apodemes anterior to coxal fields III. Anus posterior ventral, flanked by cupules ih. Claparede’s organs absent.

Dorsum. Cuticle transversely striate, striae with mammilations. Four pair of protuberances on podosoma: weak projection between si and se, three pairs longitudinally arranged between dorsal setae c1–c2, and e1–e2. Prodorsal sclerite elongate, bearing uneven scales, no anterior projections. Supracoxal gland openings very large, positioned on well sclerotized podocephalic canal. Supracoxal seta short, positioned in canal but not projecting from it. Sejugal furrow absent. Idiosomal setation complete for larval Astigmata except seta ve absent. Most idiosomal setae moderately long, distinctly barbed, but se, h1, and h2 longer. Three pairs of cupules dorsally: ia between c2 and cp, im between d2 and e2, ip lateral to h1. Opisthosomal gland openings medial to cupules im.

Legs. Legs slender, all segments freely articulated. Tarsi elongated, especially tarsus III. Setation: tarsi 10-9-6; tibiae 2-2-1; genua 2-2-1; femora 1-1-0; trochanters 0-0-0. Tarsi I– III with dorsal seta d elongate, proximal ventral setae r and w absent. Leg setae filiform with the following exceptions: setae p and q spine like; seta cG / mG on genua I–III stout and barbed. Solenidia: tarsi 1-1-0; tibiae 1-1-1; genua 2-1-1. Famulus present on tarsus I. Pretarsi I–III with large and strongly hooked empodial claws and membranous ambulacra; two thin condylophores approximating the base of empodial claws.

Protonymph ( Figures 6A,B )

Body rounded, length 264.0 (230.0–315.0), width 186.0 (162.5–230.0), N 510. General form as in larva with ontogenic changes as noted. Gnathosoma and chelicerae as in larva.

Idiosomal venter. Coxal apodeme IV and posterior apodeme of coxal filed III added. Genital valves and a pair of genital papillae added. One pair of genital setae (g) around genital region added. External walls of genital atrium with crescentic sclerotizations present. Anal region with three pairs of filiform, paraproctal setae (ps1, ps2, ps3) added, ps1 postero-dorsoventrally, ps2 and ps3 laterad of anus.

Dorsum. All dorsal setae absolutely present, setae d1, e1 longer. Only the second anterior pair of protuberances present as in larva.

Legs. Legs as in larva with following changes: solenidion omega-2 added anteriorly on tarsus I; mG on genua stout and barbed; leg IV added, with six setae on tarsi, five setae (p, q, e, f, d) as in tarsus III, s absent and w added, filiform.

Tritonymph ( Figures 7A,B )

Body similar in form to protonymph, length 410.8 (357.5–535.0), width 259.5 (230.0– 312.5), N 510.

Gnathosoma . As in protonymph.

Idiosomal venter. With following modifications from protonymph: a pair of genital valves seta 4a added; alveoli of seta ad3 visible anterior to anus.

Dorsum. Similar to protonymph except seta e1 and h1 relatively shorter. Propodosomal sclerite laterally with alveoli of setae ve. Podosomal protuberances very weak. Cuticle with small mammilations dorsally, becoming striate ventrally.

Legs. Generally similar to protonymph with additions of trochanter setae pR, sR I-III and tarsal seta s on leg IV and solenidion omega-3 on leg I positioned apically.

Female ( Figures 8 , 9 )

Body form similar to tritonymph, length 575.3 (487.5–745.0), width 371.0 (350.0– 400.0), N 510.

Gnathosoma . As in tritonymph.

Idiosomal venter. As in tritonymph but with functional genital structures. Ovipore between coxal field I–II; epigynal apodeme between and fused to anterior apodemes I; two pair of rounded genital papillae under middle of valves. Anus ventral, with pseudanal seta ps2 and ps3 as in tritonymph. Setae ad3 displaced far anterior to a position behind ovipore, long and filiform. Copulatory opening ventroterminal, behind anus, the region with strong sclerotization. Duct to bursa copulatrix (BC) long, broadly funnel shaped near BC with very wide connection to bursa. DORSUM. Similar to tritonymph except all idiosomal setae relatively shorter and more variations in length and shapes as in Fig 11 . Pattern of mammilations different from tritonymph, propodosoma with linear rows but opisthosoma with larger dots.

Legs. Similar to tritonymph in form and setation with tarsi relatively longer.

Male (Figures 10,11)

Body similar to tritonymph, length 518.3 (475.0–562.5), width 328.0 (307.5–362.5), N 510.

Gnathosoma . As in tritonymph.

Idiosomal venter. Genital region between coxal fields III–IV, with two sclerotized valves bearing short spine-like setae g; setae 4b longer, anterior to genital region. Filiform setae ps3 displaced anteriorly onto posterior edges of genital valves. Aedeagus covered by sclerotized valves, difficult to see; aedeagus with a pair of long basal supporting apodemes and very short median apodeme. Anus positioned as in tritonymph. No vestige of ad setae present.

Dorsum. Similar to female.

Legs. Similar to female with following exceptions: proral setae (p and q) completely absent on tarsi II–IV; pretarsal condylophores fused together and connected basally to an emergent, bifurcate ventral process at base of pretarsus.

Differential diagnosis

Sennertia alfkeni differs from other known species of the genus in two discrete states. In the larva the prodorsal sclerite bears uneven scales while the sclerite is smooth and lacks particular patterns in other described species. Also in the adult female a circumference of the copulatory opening is well sclerotized, while the sclerite is much smaller or indistinct in the others.

Variations in setal morphology

Among idiosomal dorsal setae, sce was almost always BB, while all the others except c1 and h3 were only sometimes BB. Each BB seta: sci, d1, d2, e1, e2, f2, and h1 were significantly shorter than each NB seta (Table 2). Although seta c 1 with BB form was also shorter than c1 with NB, the seta rarely appeared broad. The majority of offspring of females with BB and NB morphology was NB, but the percentage of BB offspring was much higher if the mother was BB ( Table 4). There was no relation

stage of

between order of birth and setal morphology. However, in broods with BB mothers, there were more BB males than BB females (x 2 test, p,0.05).

The setae in immatures were also variable in length but dorsal setae as broad as in adults never occurred. Dorsal setae in larvae seemed less variable than in the other stages (Table 2).

Life history traits and life cycle of S. alfkeni

We collected carpenter bee nests at four stages of provisioning: (1) the first stage of nesting (a nest tunnel as deep as the body length of the bee, two samples); (2) the second stage (the tunnel was probably finished but not yet provisioned, one sample); (3) the third stage (a provisioned cell before oviposition by the bee, one sample); (4) the fourth stage (an egg was laid and partitioning was completed, two nests with multiple cells). We found mites present in all stages of nesting; only deutonymphs and tritonymphs in the first and the second stages, all mite stages in the third stage, and all except deutonymphs in the fourth stage. The first disembarkation thus occurred at the initial stage of nesting when the host started excavating a dead tree branch ( Figure 12 ). Although only one bee successfully went beyond the second stage of nesting in the rearing cage, five out of six females made tunnels. In all nests, both alfkeni - type and japonica - type deutonymphs or deutonymphal exuvia were collected; in one of them (at the third stage), six out of 17 deutonymphs collected inside the nest were of the japonica - type. We also found deutonymphs in wood particles scraped out from four out of six nests. Both types of deutonymphs were found; approximately 17% deutonymphs collected from particles were of the japonica - type. There were no deutonymphs on the flowers visited by bees.

The moult from the deutonymph to the tritonymph occurred probably by stimuli of woody substances ( Table 5). Approximately half of alfkeni - type deutonymphs moulted to tritonymph responding to the substance(s), although only a few japonica - type deutonymphs moulted to tritonymphs. The cause of the difference in the response between two types was not clear in this study. There was no significant difference between female and male developmental period from egg to adult at 25 ° C (Kolmogorov–Smirnov test, p.0.05). Female ratio in broods was 0.556 (the number of mothers was seven, the total number of offspring was 194). Based on the developmental period of the mite at 25 ° C ( Table 6) and bee development at the same temperature, the mites could produce two generations during the host development from egg to adult. Mites of each ontogenetic stage contained a large quantity of pollen in their digestive tracts. Nothing else, such as fungal hyphae, was found in their feces or gut contents under a microscope. The deutonymphs collected after termination of feeding never moulted to tritonymphs with fresh pollen.

x

We observed mite development in four host cells with immature bees ( Figure 13 ). When we opened the nests with juvenile bees, there were tens of mites in each cell. As long as pollen mass existed, the mites aggregated on or inside the loaf and fed on it. After the host excreted fecal pellets (meconium), the mite also fed on them. When the host pupated, many protonymphs assembled on the host surface, particularly around and in various grooves on the ventral surface prior to going into the quiescent stage. They eventually moulted to deutonymphs although many mites in other feeding stages remained around the fecal pellets. Some of these moulted to deutonymphs before host emergence and the others did so afterward. Although it was not quantitatively examined, the first deutonymphs tended large in the idiosomal size. The deutonymphs gradually moved from the pupal exuvium onto the emerged host surface and attached to the mesosoma, mesosomal and metasomal acarinaria, and occasionally the head and wings. Although we did not trace the feeding stages remaining in the cells, we suspect that they were eventually swept from the bee nests (n 56) because the nest inside after new adult bees emerged were clean, without feces, mites and partition walls.

Figures

Figure 5. Sennertia alfkeni, larva: (A) dorsum; (B) venter.

Figure 6. Sennertia alfkeni, protonymph: (A) dorsum; (B) venter.

Figure 7. Sennertia alfkeni, tritonymph: (A) dorsum; (B) venter.

Figure 8. Sennertia alfkeni, adult female with NB setae: (A) dorsum; (B) venter.

Figure 9. Sennertia alfkeni, adult female: (A) Leg I and tarsus I; (B) Leg II and tarsus II; (C) Leg III and tarsus III; (D) Leg IV and tarsus IV.

Figure 11. Sennertia alfkeni, dorsum of adult male with BB setae.

Figure 12. The number of deutonymphs collected from wood particles swept out by tunnelling carpenter bees. Five host individuals were indicated with different legends (squares, circles, diamonds, triangles and cross). Mites were not collected from the particles by individuals indicated with the triangle and cross. Colour differences in the same legends (black and white) meant that the same individual tunnelled twice.

Figure 13. The life cycles of the mite Sennertia alfkeni (black bars) and the carpenter bee Xylocopa appendiculata circumvolans (white bars). E5egg; L5larva; P5pupa; PN5protonymph; DN5deutonymph; TN5tritonymph; A5adult.