J.G. Stoffolano

Distribution of haemocytes in larvae of Musca domestica and Musca autumnalis and possible chemotaxis during parasitization

Abstract In each of the three larval instars of Musca domestica and M. autumnalis most of the haemocytes were accumulated in the haemocoele in the last two segments of the body. Very few circulating haemocytes were found, and only in second- and third-stage larvae. During development the posterior haemocytic masses increased in size. At the time of pupation the haemocytes were completely dispersed throughout the haemocoele. Experiments with ligated larvae and larvae fixed in liquid nitrogen indicated that the posterior haemocytic masses were not artifacts of fixation. It remains to be determined whether these posterior masses represent haemocytopoietic tissue. The possibility that the haemocytes exhibit chemotaxis during pupation and in response to parasitization is discussed.

Influence of age on the electroantennogram response of the female blowfly (Phormia regina) (Diptera: Calliphoridae)

Abstract By means of electroantennogram recording techniques, we have monitored the antennal olfactory sensitivity, from the time of eclosion until complete egg maturation, of female blowflies (Phormia regina) fed either a protein diet or a protein free one. The tested stimuli were swormlure-4 (SL-4) which is a potent lure for calliphorid flies, 1-hexanol as a reference stimulus and air as a control. After taking the electroantennograms, egg and ovarian development were evaluated. Stimulation with SL-4 and 1-hexanol evoked electroantennograms increasing in amplitude with age regardless of whether or not flies were fed protein during the first 5 days of adult life. In the protein-fed flies eggs were fully developed whereas those of the no-protein group remained undeveloped. The peak olfactory sensitivity occurs at a time when the female fly begins to search for an oviposition substrate.

Allatotropic activity in the brain of female Phormia regina (Diptera: Calliphoridae).

In Phormia regina, the rate of juvenile hormone (JH) synthesis rises rapidly after the ingestion of an adequate protein meal. In a previous publication we have localized the neurons containing Manduca sexta allatotropin (Mas-AT)-like substances in the brain of P. regina and demonstrated the allatotropic effect of synthetic Mas-AT in sugar-fed flies in vitro. In this current study, we examined the possible role of the brain of P. regina after the fly received a protein meal. In vitro studies showed that the brain releases, at 8 h after a protein meal, a factor(s) with a strong allatotropic effect. This factor(s) stimulates the corpus allatum (CA) to produce 6.9 times more juvenile hormones (JHs) than the control CA. Time course studies showed that the release of this allatotropic factor(s) is temporally controlled. Only the brains collected from flies at 6 and 8 h after the onset of a liver meal release allatotropic factor(s). Injection of anti-Mas-AT antiserum partially suppressed the fly follicle development in vivo. Presence of anti-Mas-AT antiserum decreased the allatotropic effect of the brain released allatotropic factor(s) in vitro. In addition to a Mas-AT-like substance, it is possible that the brains of liver-fed P. regina females may synthesize other allatotropic factors that are chemically unrelated or partially related to Mas-AT, which cannot be recognized/neutralized by our anti-Mas-AT antiserum.

Sensitivity to albumin and its terminal amino acids of labellar taste chemoreceptors in Protophormia terraenovae (Diptera: Calliphoridae)

Abstract Stimulation with bovine serum albumin (BSA) evokes spikes discharges from three receptor cells of the labellar chemosensilla in Protophormia , the “sugar” cell being the most sensitive. Confrontation of the spike frequency profiles across all three chemoreceptor cells by the vector space analysis suggests that l -alanine (the C-terminal amino acid of the BSA molecule), but not l -aspartic acid (N-terminal amino acid), may account for the stimulator effectiveness of BSA.

Effect of Seasonality and Perisulfakinin on Engorgement by Tabanus nigrovittatus (Diptera: Tabanidae) in the Laboratory

Abstract The horse fly Tabanus nigrovittatus Macquart (Diptera: Tabanidae), a hematophagous insect, is a nuisance pest along the Atlantic Coast. A description of the engorgement pattern throughout the season is lacking in the literature for this species. The percentage of flies engorging a bloodmeal in the laboratory throughout the season was recorded, and here we demonstrate that the percentage of flies that are blood feeding fluctuates, leading to a decrease in flies engorging as the season ends. Additionally, three recent nonhematophagous insect studies demonstrated that sulfakinins, a vertebrate homologue of cholecystokinin, function in feeding inhibition as a satiety factor. We found that groups of flies injected with one nanomole of perisulfakinin were inhibited from blood feeding by 45–60%. The satiation of feeding reported here is in agreement with the previous research by using nonhematophagous species. When groups of flies were injected with 10 nmol of perisulfakinin, the percentage of flies engorging was increased relative to the sham-injected flies, although not significantly. The stimulation of engorgement by sulfakinin has not previously been demonstrated, and its mode of action remains unclear.

EFFECTS OF ATP ON THE INTERACTION OF ALBUMIN AND ITS C-TERMINAL AMINO-ACID L-ALANINE WITH THE SUGAR RECEPTOR CELL IN PROTOPHORMIA-TERRAENOVAE (DIPTERA, CALLIPHORIDAE)

Abstract Stimulation with bovine serum albumin (BSA) and its C-terminal amino acid l -alanine evokes spike activity from the “sugar” cell of the labellar chemosensilla in Protophormia. The presence of ATP in the BSA solution strongly enhances this effect, but is pH-dependent. On the contrary, addition of ATP to the l -alanine solution inhibits the “sugar” cell response regardless of pH. Reception mechanisms for BSA and l -alanine are discussed.

Feeding responses of the horsefly, Tabanus nigrovittatus (Diptera; Tabanidae) to purinergic phagostimulants.

Abstract Each year in late June, 1982–1986, the phagostimulatory potencies of purinergic compounds (ATP and derivatives of ATP) were tested on wild-caught female Tabanus nigrovittatus. In all, 15 compounds were investigated. They were dissolved in 0.15 M sodium chloride solution and presented at 37°C in an artificial feeding apparatus in which the flies fed upward through a Parafilm M® membrane. Potencies ranked, ATP > ADP > 2′dATP > ATP-γ-S = 2′dADP > AMP-PCP = AtetraP > AMP-PNP = 2′3′dd-ATP = AMP = APS. 3′dATP, Ara-ATP, and Ado were very weak phagostimulants and c-AMP induced no gorging at 1 mM. Previous work that reported ADP > ATP was an error. The average ED50 for ATP is 21.2 μM and ADP is 39.3 μM. Any changes in the phosphate chain of ATP caused a significant reduction in potency. Removal of the oxygen at the 3′ position on the ribose reduced potency much more than its removal at the 2′ position. Substitution of solvents other than the sodium chloride solution changed ED50 values for ATP and ADP. Addition of 5% bovine albumin and 10 mM sodium bicarbonate to the 0.15 M sodium chloride increases the potency of ATP nearly 3-fold and the potency of ADP by more than 7-fold. ADP dissolved in choline chloride was as potent as ADP in sodium chloride solution. Addition of calcium ions to the solvent reduced the potency of ADP, probably because of the activation of apyrase enzymes. The potency of ADP was determined each year as an indicator of seasonal variability. Its ED50 values ranged from 33.3 μM in 1982 to 45.7 μM in 1983. June 1985 was unusually cold and the ED50 value for ADP was 92.7 μM. Data from 1985 were segregated from the other data. Seasonal effects must be considered when field-collected insects are used.

OBSERVATIONS ON THE MORPHOLOGY AND ELECTROPHYSIOLOGICAL RESPONSES OF LABELLAR, TARSAL AND PALPAL CHEMOSENSILLA OF THE BLACK FLY, SIMULIUM DECORUM WALKER (DIPTERA SIMULIIDAE)

SUMMARY The presence of taste chemosensilla was demonstrated, by using both morphological and electrophysiological techniques, on labella, tarsi, and palps of a laboratory-reared colony of Simulium decorum Walker (Diptera Simuliidae). Each type of chemosensillum was sensitive to NaCl or sucrose stimulation, and proved to consist of four chemosensory units. The presence of various chemosensory units in each sensillum allows the assumption that in S. decorum single sensilla may provide the CNS with adequate information for peripheral discrimination among the stimulating chemicals, possibly by providing different spike discharge patterns according to the quality of the stimulus.