The status of weed-associated populations of the brown planthopper,Nilaparvata lugens (Stål) - host race or biological species?

Populations of the brown planthopper, Nilaparvata lugens (Stål), from the Philippines were collected from and reared on the grass weed, Leersia hexandra Swartz. Six different populations from five localities were studied and compared with a sympatric rice-feeding population.
Experiments on survival, virulence and oviposition preferences demonstrated that populations from one host plant survived poorly on the other and showed a strong preference for the species from which they derived. Crosses between the two populations showed some barriers to hybridization, but viable and fertile hybrids were obtained. Mate choice experiments demonstrated that, when a choice was available, no heterogametic matings occurred.
Pulse repetition frequencies of female and male calls differed consistently and significantly between rice- and Leesia -associated populations. Hybrid calls were intermediate between the parental calls. Playback experiments showed that the call differences were primarily responsible for maintaining the identities of the host-associated populations.
It was concluded that the populations from rice and from L. hexandra represent two distinct, but very closely allied, sympatric species in the Philippines.     

Cell Death and Acid Phosphatase Activity in the Regenerating Planarian Polycelis tenuis Iijima

A combination of microscopical, cytochemical, and biochemical techniques have been employed to study the changes occurring during the first seven days of blastema formation and regeneration after decapitation in adult Polycelis tenuis worms. Fine structural data reveal evidence of cell fragmentation, selective cell deletion, and phagocytosis at and below the wound surface. Initially, (0–12 h regeneration) cell debris is phagocytosed by intact parenchymal and gastrodermal cells near the cut surface which is later sealed (24 h) by a stretching of marginal epidermal cells. Wound sealing is followed by a migration of newly differentiated rhabdite cells into the epithelium. Morphological evidence of a selective cell autolysis precedes evidence of an accumuluation of lipid and glycogen reserves in the parenchymal and gastrodermal cells and the later (48 h regeneration time) aggregation of undifferentiated mitotically active neoblasts beneath the wound.
Biochemical data reveal an early period of high acid phosphatase (p-nitrophenyl phosphatase and sodium-β-glycerophosphatase) activity 3–12 h after injury, followed by a further intense period of activity at 44–48 h after decapitation. The coincident cytochemical data show an increased level of acid phosphatase activity associated with cell lysis and death in the wound and blastema zone and also with the digestion of phagocytosed cell debris.