Robustocheles (R.) deltacus Abou-Awad, El-Sawaf and Abdel-Khalek

Abou-Awad, B. A., El-Sawaf, B. M., Reda, A. S. & Abdel-Khalek, A. A., 2011, Comparative Morphological And Biological Studies Of Two Rhagidiid Mites: Robustocheles (R.) Deltacus And Rhagidia (R.) Qaliubiensis, Acarologia 51 (3), pp. 381-393 : 384-386

Robustocheles (R.) deltacus Abou-Awad, El-Sawaf and Abdel-Khalek

Robustocheles (R.) deltacus successfully developed from egg to adult when fed on fungi, but failed to lay eggs. When rhagidiid predator was reared on different prey, adult female laid eggs. Thus, fungi diets were found insufficient to induce oviposition.

Table 1 shows that R. (R.) deltacus passed through the egg, larva (immobile calyptostatic prelarva and mobile elatostatic larva), proto-, deuto-, tritonymph and adult stages. F. oxysporum slightly shortened the period of immature and adult stages than did the two other fungi F. solani and T. harzairum .

Life cycle and life span were significantly shorter (42.9 and 57.9 days) when rhagidiid predator fed on F. oxysporum , while being longer on other fungal diets.

Feeding R. (R.) deltacus on larvae of springtail L. insertus accelerated the development by giving significantly shorter period of immature stages than obtained on the tydeid mite T. aegyptiaca and the housefly M. domestica ( Table 2). The quiescent larvae, proto-, deuto- and tritonymph showed almost the same trend of differences and comprised 26.4%, 19.4% and 19.7% of the total duration of the life cycle, when feeding on the three prey, respectively. The whole life cycle averaged 32.5, 36.0 and 39.0 days on each prey, respectively.

Female laid its eggs on walls of plastic cells or slits of substratum in clusters of about 5- 9 eggs. Eggs are elongated ovate. They measure about 245– 265 µm long and 190 – 210 µm wide in outline. Newly laid eggs are dark orange. As incubation proceeded, the embryo gradually appeared and increased in size; just before hatching a longitudinal split occurred in the egg and subsequently the hatched calyptostatic prelarva pushed its self outside the egg shell. It is translucent white, immobile and nonfeeding. After hours it becomes mobile elatostatic nonfeeding larvae.

Quiescent immature stages occurred in protected sites such as holes, cracks and slits of substratum. Individual spins a copwebby moulting nest or a thin layer of translucent membrane around its self. Moulting process or ecdysis took about 8 hours. Preoviposition and oviposition periods were almost the same on the three preys, but prolonged postoviposition. On L. insertus, the adult female life span appeared to be significantly shorter than obtained on M. domestica (Table 3).

It is worth mentioning that the food type seemed to affect the predator’s colour, as immatures and adult stages were whitish, rosy and dark grey when individuals fed on the fungi F. solani , F. oxysporum and T. harziarum respectively. On larval prey, these individuals acquired a whitish appearance. Predator female and male consumed significantly greater number of T. aegyptiaca immatures than those of L. insertus and M. domestica larvae ( Table 4). The daily rate for female prey averaged 10.24, 6.12 and 3.22 individuals and that of male reached 9.93, 5.79 and 2.83 individuals of the three prey species respectively ( Table 4).

Individuals were usually seen fast wandering into rearing cells, searching for their prey. When meeting the prey, the predator grasped the prey’s appendages using its palps and the first pair of anterior legs, then it inserted its chelicerae into the prey at mid of its body to suck partially the prey content. After a while, the predator returned to attack again the same prey to continue the sucking process and consume entire prey. This process lasted about three minutes.

Zacharda (1980) mentioned that rhagidiid species have cheliceral shears, often arched and evidently adapted to grasping a mobile prey. The subcapitulum of these mites have labra and internal malae conspicuously styletform and probably also piercing a prey grasped with the chelicerae. During life span, the female and male predator fed on an average 687.4 and 502.2 T. aegyptiaca immatures, 473.2 and 302.7 L. insertus larvae and 194.6 and 185.9 larvae of M. domestica , respectively. The total number of deposited eggs/female averaged 15.10, 12.60 and 11.60 eggs, when fed L. insertus and M. domestica and T. aegyptiaca , respectively( Table 4). Feeding on springtails increased female fecundity more than housefly and tydeid mites.

The data in Table 5 show that the multiplication per generation (RO) was 12.82, 12.09 and 8.19 times in a generation time (T) of 37.75, 43.93 and 46.03 days, while the intrinsic rate of increase (rm) averaged 0.0676, 0.0567 and 0.0457 individuals per days, when R. (R.) deltacus fed on L. insertus, T. aegyptiaca and M. domestica , respectively. Thus, it can be concluded that the reproduction rate was the highest on L. insertus prey. Larvae of springtail also gave the highest females ratio in the sex ratio as compared to feeding on both other prey ( Table 5).