Diel sugar feeding and reproductive behaviours of Aedes aegypti mosquitoes in Trinidad: with implications for mass release of sterile mosquitoes

Studies on the diel sugar feeding periodicity of male and female Aedes aegypti were conducted under laboratory conditions and monitored in single cages using the polyphagometer device and examined every 2h. Males mosquitoes displayed two peaks in sugar feeding, a small morning peak at 06.00-08.00 h (16% of sugar feeding) and a significant evening peak at 16.00-18.00 h (40% of sugar feeding). A similar pattern was observed among females: a small early morning peak (18% of sugar feeding) and a significant peak in the evening 16.00-18.00 h (42% of sugar feeding). Studies on the effects of sugar feeding on the excitation of males showed 100% erect antennal fibrillae after 36 h. In contrast, only 15% of the water-fed males responded. Laboratory studies on the effects of sugar feeding on the insemination rates of A. aegypti females showed similar inseminations rates among sugar and water fed males but after 4 days all water fed males died while the sugar fed males continued to survive and inseminate females. The synchronization of the male and female diel sugar feeding periodicity is discussed in the context of sterile insect techniques or genetic control methods.

The diel copulation periodicity of the mosquito, Aedes aegypti (L.) (Diptera: Culicidae) at indoor and outdoor sites in Trinidad, West Indies

The diel copulation periodicity of domestic Aedes aegypti in the field in Trinidad, West Indies was monitored weekly at indoor and outdoor sites over a 16 month period. At indoor sites two significant (P<0.02) peaks in copulation occurred between 06.00 and 08.00 (25% of copulation events) and between 16.00 and 18.00 (24%): at outdoor sites the copulation periodicity was similar to that observed indoors with an early morning peak in copulation at 06.00-08.00 (30%) and a late evening peak at 16.00-18.00 h (25%). Laboratory studies showed similar copulation patterns to those observed at indoor and outdoor sites. Copulation occurred at two different locations: at outdoor sites copulation was primarily in close proximity to breeding sites while at indoor sites copulation was observed in close proximity to human bait or members of the household. The parity rate of copulating females collected indoors was 59% in contrast to only 15% collected outdoors, which suggests that females found indoors were older. The diel copulation periodicity, location where copulation occurs, parous rates and insemination rates are discussed in the context of sterile insect technique or genetic control modalities.

Studies on the post-oviposition blood-feeding behaviour of Aedes aegypti (L.) (Diptera: Culicidae) in the laboratory

The blood-feeding behaviour of the Trinidad strain of Aedes aegypti was studied, under laboratory conditions, using one female per cage and monitoring blood feeding immediately, 12, and 24 hours after oviposition. To get large numbers of females that had newly completed their first gonotrophic cycle, the diel oviposition periodicity was conducted using single females per cage and monitoring at 2-hour intervals. The diel oviposition periodicity showed a small morning peak (8%) during the first 2 hours of the photophase after which oviposition declined: during the second half of the photophase, oviposition increased reaching a peak comprising 56% of eggs (G = 59·9, P>0·01) between 16:00 and 18:00 hours. At post-oviposition hour 0, only five (10%) of the females accepted a blood meal but at post-oviposition hour 12, significantly more (G = 46·98, P>0·02) females, 35 (70%) accepted a blood meal. This pattern was consistently observed when females were offered blood meals at 12 and 24 hours after completing their first gonotrophic cycle. Multiple feeding was observed among the blood-feeding females and the results of this study are discussed in the context of disease transmission patterns and physiological mechanisms which control their blood-feeding behaviours.

Sampling considerations for designing Aedes aegypti (Diptera:Culicidae) oviposition studies in Iquitos, Peru: substrate preference, diurnal periodicity, and gonotrophic cycle length

When devising methods to sample Aedes aegypti (L.) eggs from naturally-occurring containers to investigate selective oviposition, failure to take into account certain aspects of Ae. aegypti behavior can bias study inferences. In Iquitos, Peru, we tested three assumptions related to designing Ae. aegypti oviposition field studies, as follows: 1) lining containers with paper as an oviposition substrate does not affect oviposition; 2) diurnal egg-laying activity peaks in the late afternoon or early evening, and there is little oviposition during midday; and 3) the gonotrophic cycle length of wild females averages from 3 to 4 d. When wild females were presented with containers lined and unlined with paper toweling, the presence of paper increased oviposition in plastic and metal containers, but had no effect in cement containers. Recording the number of eggs laid by Ae. aegypti every 2 h throughout the day delineated a bimodal diurnal oviposition pattern, with a small morning peak, decreased activity during midday, and a predominant peak in the late afternoon and evening from 16:00 to 20:00 h. Daily monitoring of captive individual Fo females revealed that the gonotrophic cycle length was typically 3-4 d for the Iquitos population. These findings will be used to adjust field study design to 1) account for sampling eggs using paper toweling, and 2) determine the time of day and number of days over which to sample Ae. aegypti eggs. We explored how failure to consider these behaviors could potentially bias field assessments of oviposition preferences.

The diel oviposition periodicity of Aedes aegypti (L.) (Diptera: Culicidae) in Trinidad, West Indies: effects of forced egg retention

The diel oviposition periodicity of two groups of Aedes aegypti females (Trinidad strain), (i) thoses allowed access to oviposition sites and (ii) females forced to retain-eggs for four days, were studied under laboratory conditions using one female per cage and monitoring by changing substrates every two hours. The individual females which were allowed access to oviposition sites showed peak oviposition between 16.00-18.00 h (50% of eggs), whereas individuals forced to retain eggs for four days showed a similar pattern but with a significantly (P<0.001) larger peak oviposition between 16.00-18.00 h (94% of eggs). However, females forced to retain eggs laid most or all of their eggs in one container (84%), while females given access to oviposition sites distributed their eggs among 2-4 containers. The results of this study are discussed in the context of the strength of the circadian rhythms, oviposition strategies and its impact on vector control activities.