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Paper text:
it has been estimated that introduction will succeed only if fitness is greater than 80% .
one of the prime targets for such modification is anopheles gambiae , one of the primary vectors in sub - saharan africa , where more than 90% of the world 's malaria is transmitted . whilst size of males
females that mate with males that are two days old may be more likely to oviposit than if they mate with older males . hence
, younger males may be fitter and , for the introduction to succeed , released males will need to mate with wild females early in their life . in many areas of africa
funestus is likely to have little long - term effect on malaria in many areas .
given their sympatry and the likelihood of a similar mating period , some aspects of the mating behaviour of an .
gambiae , like many other anophelines , mating is associated with swarming [ 5 - 9 ] .
funestus , however , is that of harper   who observed swarming males on the threshold of a thatched dwelling 1 km from nyanza , lake victoria . indeed
the doyens of african medical entomologists , gilles and de meillon , in their extensive review   state , ' we have never found them ( swarms ) ourselves , even in areas of high density ' . an .
the greater the contrast the more likely will a swarm form and they can be induced to form over artificial markers .
although thought to be a eurygamic species ( which requires large volumes of space to successfully mate ) harper   describes an .
no marker was described and no mating was recorded despite the fact that estimated numbers in the swarm , which stretched almost a metre across , exceeded 500 . in a recent study of swarming behaviour of an .
, , however , considered that swarm site and marker were unlikely to be specific to a particular species .
they also threw doubt on the idea of ' swarm arenas ' proposed by charlwood and jones .
funestus were commonly observed , in a village in southern mozambique , in areas similar to those used by an .
funestus in these areas and to determine if any aspects of the observed behaviour differed from that recorded for the m form of an .
the study took place on nineteen evenings between the 23march and 3may 2002 , in the village of furvela , 650 km north of maputo and 7 km south of the town of morrumbene , in the province of inhambane , on the main maputo - beira highway ( en1 ) .
the village lies circa 3 km from mangrove - bordered coast and is delineated by the furvela river a small stream within a 2 km wide valley .
most of the villagers live by subsistence farming , growing maize , manioc , peanuts and beans .
cashew nut trees and coconut palm are common . in the river valley sugar cane , dry rice and bananas are grown .
direct observation of swarms was undertaken in the manner described by charlwood & jones   and charlwood et al . , .
swarming males and insects in copula were collected by sweep net , modified in the manner described by marchand .
artificial markers used were the same as those used in so tom . in order to determine whether size affected likelihood of a male swarming or mating the wing lengths of males collected resting , exiting houses , swarming and mating were measured .
collections of indoor resting insects were performed , with a torch and aspirator , for 10 minutes in buildings shown in figure 1 and exiting insects at dusk were monitored by placing a conical , double - size bednet over the gable - ends of houses within the study area .
map of four sites in which swarms of anopheles funestus were observed , furvela village , mozambique .
wing lengths , between the alula notch and the wing tip , excluding scales , of unselected samples of insects from all collections were measured using an ocular micrometer on a stereoscope to the nearest 0.03 mm .
wing lengths of the different groups were compared using anova . in order to determine if differences in flight sound between an .
gambiae , which might swarm together , differ ( and therefore may act as potential barrier to prevent hybridization ) the frequency distribution of individual insects , in free flight confined inside netting covered paper cups , was determined according to the method outlined in brogdon .
briefly , recordings of individual insects were made with a microphone ( a sony ecm - d870p ) either directly onto a portable computer or onto mini - disc and then transferred to computer and stored as wave files .
the files were digitally sampled at 20,000 hz and then re - sampled at 5,000 hz and sonograms , plots of sound frequency versus time , prepared using computer software ( spectrogram , public domain by richard horne ) .
temperature data was obtained for the two nearest weather stations ( inhambane and vilanculos ) available from the noaa website   and the mean value used .
there was , however , no obvious pattern as to the location of the swarms which could be at the edge or in the middle of the clearing ( figure 1 , figure 2 ) .
swarms occurred 24 m off the ground , occupied a similar volume , and appeared to consist of a similar number of insects . at some sites two or more swarms occurred within a few metres of each other ( figure 1 ) .
it was not possible to determine with any certainty , what the characteristics were that enabled males to maintain their position .
at the site closest to the river valley ( the putative breeding site ) the swarm occurred in a gap in vegetation that was illuminated by the western sky ( figure 1a ) . when this gap was artificially closed ( by extending a sheet across it ) males flew higher ( so that they continued swarming in a gap ) .
two further swarms were discovered by looking for such gaps , and similar profiles occurred at other swarm sites , although in all other cases the ' silhouette ' was created at a much greater distance from the place where the swarm occurred .
it was rarely possible to see the first male at the swarm site ; rather , several insects started swarming at the same time .
numbers rapidly built up and within five minutes of the start had reached maximum size and density . on two occasions , dragonflies ( libellula sp . )
on one occasion all four males in a swarm were caught and eaten in a matter of seconds .
funestus were collected from a swarm of apparently larger insects that formed close to a higher and larger swarm from which 1 an .
funestus were collected swarming ( a total of 601 males from 13 swarms ) in sharp contrast to the an .
gambiae from so tom , swarming males avoided black or white horizontal markers and dispersed when these were introduced under the swarm . despite there being a considerable number of male an .
the number and time of pairs in copula was noted on 9 evenings of observation .
the time at which the first pair was observed , relative to the time of the start of swarming , was inversely proportional to the total number observed throughout the swarming period ( figure 3 ) limitation of resources meant that comparisons between sites on the same day were unavailable .
3.7 min after the start of swarming and had reached a maximum 4 min later . by the end of the observation period ( when it became impossible to see the insects with the naked eye ) numbers of mating pairs had almost declined to zero ( figure 4 ) .
relationship between the time of the first copula observed after the start of swarming and the total number of pairs subsequently counted .
number of pairs of anopheles funestus observed relative to the start of swarming , itself co - incident with sunset .
all were newly emerged with undeveloped ovaries . of the 71 unfed females dissected from resting collections 68 were virgins .
the number of unfed females and males resting inside houses were positively associated ( figure 5 ) but there was no association in the number of either of these categories with gravid and blood fed insects in resting collections .
relationship between the number of males and unfed ( virgin ) females collected resting inside houses , furvela village , mozambique .
overall both male and female wing size distributions were approximately normal and were not significantly different ( figure 6 ) .
the wing length of males from resting collection , leaving houses , collected from swarms and in copula was similar ( table 1 ) ( figure 7a ) .
the mean wing size of males differed according to collection site ( one - way anova for 2 d.f .
, p = 0.037 ) . among the females , those collected in light - traps ( i.e. host seeking ) were smaller than the other categories ( figure 7b ) .
the wing size of females collected in copula were similar to that of newly emerged insects collected resting or exiting from houses .
wing length distribution of male and female anopheles funestus from furvela village , march - may 2002 .
winglength of male anopheles funestus collected at different phases of the activity cycle , furvela village , mozambique . during the period of study temperatures dropped from an average of 29c to 26c .
female wing sizes increased over this period but male size did not ( figure 8) .
mean male and female wing length of anopheles funestus and ambient temperature from furvela village , mozambique , by date of collection .
funestus were so common in furvela that it is strange that they have not been observed elsewhere .
they differed from those recorded by harper   in that they all occurred in very open spaces several metres off the ground rather than the threshold of houses a few centimetres off the floor .
anopheles funestus is now known to belong to a group of species , some of which are non - vectors   and it is not certain which member of the group the author had observed .
gambiae seen in so tom . in both species they occurred at sunset 24 m above the ground in relatively open areas .
swarm size , dimensions and the estimated number of males per swarm appeared to be relatively constant between sites and species but the number of females entering swarms showed considerable variation .
swarm sites , each of which has a fixed capacity , may determine the dispersal of males .
one might expect relatively more mating to take place in the swarms closest to the female emergence site .
we were unable to determine the number of males in a swarm and hence unable to determine if male mating success rates were similar in the different swarms .
the fact that male and newly emerged female ratios resting in houses were relatively constant implies that location of swarm has little influence on mating success .
the lack of a relationship between either of these two groups and older females highlights the fact that entry routes , reasons for entry , sense used and time entered differs between the two categories .
males and virgin females use their eyes and enter houses at dawn usually via the darkest orifice ( which usually means windows and doors ) .
they are in search of a bloodmeal and use their sense of smell for direction . with a single exception
funestus does not seem to be required since they are only likely to encounter con - specific females . on the one evening
was obtained two distinct swarms , one of an apparently larger mosquito were seen prior to their being sampled .
the swarms occurred circa 50 cm apart , with the larger insects swarming closer to the ground .
it is not certain that the species were mixed . given that they were caught swarming at least once during the study begs the question of why swarms of an .
were not more commonly observed or induced over markers in furvela as they were in so tom .
one reason may be that the member of the complex observed in so tom was the m form of an .
it would appear to be a different species from the other members of the complex and thus may behave differently .
in particular all size groups were caught in copula , the caveat being that the numbers involved were small .
the sampled houses were situated at varying distances from the river valley , the putative breeding site .
. this may be due to the relatively large sample size or because size influenced male dispersal recently it has been shown that in small cages smaller female an .
one of the difficulties with this interpretation is that a male can inseminate four or more females whilst females are largely monogamous . given the equal sex ratio at emergence an average male will only meet a single female in his lifetime .
if so it would seem unlikely that males would be too selective since there is probably another set of genes around that is not and should a further female come along then she can still be fertilized . indeed
the size distribution of females caught in copula was not significantly different from those emerging .
as temperatures drop the duration of larval and pupal stages increase and the size of emerging insects increases . the duration of the larval stage in an .
the effect of the drop in temperature on mean female size but not male size may be because the adult males collected had not been exposed as larvae , or particularly as pupae   to such low temperatures as the females .
funestus avoided such markers ( both light and dark ) and dispersed if they were placed underneath naturally occurring swarms .
the response to potential horizontal markers is likely to be sufficient to prevent mixed swarms from occurring and this is likely to be the factor responsible for isolation between an .
charlwood conducted the work in the field and helped prepare the manuscript thompson provided logistical support to the fieldwork madsen helped prepare the manuscript , was responsible for figures and provided statistical support
jdc would like to thank marcia , elsa and luis for their help in swarm watching .
this study was undertaken as part of the mozdan project and was supported by the danish bilharziasis laboratory .
backgroundcontrol of malaria by the release of genetically modified mosquitoes refractory to transmission is now becoming a possibility . in many areas of africa , 
 anopheles gambiae is found together with an equally important vector , an . 
 funestus . given their sympatry and the likelihood of a similar mating period some aspects of the mating behaviour of an . 
 gambiae s.l . and an . 
 funestus are likely to differ . 
 we therefore attempted to characterise the swarming behaviour of an . 
 funestus and to determine if any aspects of the observed behaviour differed from that recorded for the m form of an . 
 gambiae from so tom.methodsin march  may 2002 the swarming , mating , house exiting and resting behaviour of anopheles funestus was studied by direct observation in mozambique . 
 swarming males and insects in copula were collected by sweep net . 
 wing lengths of males collected resting , exiting houses , swarming and mating were measured and the wingbeat frequency distribution of individual insects , in free flight confined inside netting covered paper cups , was also determined.resultsmono-specific swarms occurred at sunset in relatively open areas close to houses used for resting . 
 mating pairs were seen 11  3.7 min after the start of swarming . 
 the number of total pairs observed being inversely proportional to the time difference between the start of swarming and the first pairing . the great majority of females mated before feeding . 
 male or female size did not appear to affect mating success or other behaviours . during the study , 
 ambient temperatures decreased and female , but not male , wing size increased . at 516 hz , the flight tone of female an . 
 funestus was similar to the 497 hz of the local an . 
 gambiae . 
 males dispersed if light or dark artificial horizontal markers were placed underneath naturally occurring swarms.conclusiondifferential response to markers would be sufficient for swarming in an . 
 funestus and an . 
 gambiae s.l . to occur in distinct sites .