Alan S. Robinson

PROGRESS IN THE USE OF CHROMOSOMAL TRANSLOCATIONS FOR THE CONTROL OF INSECT PESTS

CONTENTS

Onion conditioning pertaining to larval preference, survival and rate of development in Delia (=Hylemya) antiqua

Using onion conditioned by Delia (=Hylemya) antiqua larvae for four different periods of time and larvae of four different ages, the effect of conditioned or fresh onion on larval preference was studied. It was shown that of the sixteen combinations tested, nine larval groups showed a preference for conditioned onion, five showed no preference and two showed a preference for fresh onion. Significantly, it was the older larvae which preferred the fresh onion. Further, it was demonstrated that the inoculation of a larval macerate to fresh onion prior to the addition of 1st‐instar larvae significantly reduced larval developmental time.

Genetic control of Hylemya antiqua. I. X-ray-induced effects in the F0 and F1 generations

Summary Dose-response relationships were established for the induction, by X-rays, of dominant lethality in the sperm of the onion fly, Hylemya antique It is concluded that lethality is a predominantly single-hit phenomenon. Nearly complete sterility was achieved with a dose of 3 kR. After incubation for 3 days at 29°C, eggs were divided into three classes: (a) empty hatched eggs, (b) unhatched brown eggs, i.e. late embryonic lethals, and (c) unhatched white eggs, i.e. unfertilized eggs or early embryonic lethals. The effect of different doses of radiation on the proportions of these three egg phenopytes was measured. All three phenotypes, when plotted exponentially, exhibited a linear response with dose. There was no effect of radiation on % pupation, % eclosion or F 1 sex ratio for the radiation doses used. F 1 s derived from seven radiation doses were test crossed with control insects. The average fertility of such groups of F 1 s was not seriously reduced until the two highest irradiation levels, i.e. 2.5 and 3.0 kR, were reached. F 1 s derived from two irradiation levels (0.2 and 0.5 kR) were examined cytologically for the presence of chromosomal rearrangements. A total of seven translocations and two pericentric inversions was found. The results are discussed within the framework of genetic control of Hylemya antiqua .

The effect of crowding on adult populations ofDelia (=Hylemya) antiqua (Meigen)

Using 5 density levels, the effect of increasing density was studied on several population statistics of adultDelia (=Hylemya) antiqua. Amongst the statistics studied were adult lifespan; female mating frequency, fecundity and egg hatchability. It was shown that females lived significantly longer than males and that increasing density significantly reduced lifespan. Density had no effect on mating frequency. Total fecundity/female was significantly reduced with increasing density but oviposition rate was density independent. Using these statistics, mean generation timeT, net reproduction rateR 0 and capacity for increaser c were calculated at the different density levels. Values ofR 0 showed a one-tailed response but there was no clear effect of density onr c . Multiple comparisons between variables revealed several important relationships. 1. Adult lifespan was the most important factor affecting egg production. 2. Number of mated females was more important in affecting total fecundity/cage than adult density. Adult lifespan was the most important factor affecting egg production. Number of mated females was more important in affecting total fecundity/cage than adult density. It could also be calculated that to produce the effect of one single mated female on total fecundity/cage the overall density would have to be reduced by 0.0023 individuals/cm3. These results are discussed in the context of efficient laboratory rearing of the onion fly.

Genetic control ofHylemya antiqua III. Differences in pupation ability between two strains

Some relevant traits of a wild (L) and a laboratory (C) strain ofHylemya antiqua (Meigen), determining differences in their pupation ability under experimental conditions have been investigated in relation to genetic control. The wild strain showed an intrinsic higher pupation ability than the laboratory strain. The minimum feeding period was 0.6 days longer for the C strain. The minimum larval dry weight was different for the two strains. With a normal feeding period C larvae pupated on average 1.63 days later than L larvae. By the shortening of the larval feeding period an acceleration of the larval development of both strains was observed: the acceleration of development was more marked for the wild strain. This result has been contrasted with published works onDrosphila. The consequences of these differences as far as the competitive ability of each strain is concerned, have been discussed in relation to genetic control.

Larval Dispersal as Related To Density in Wild and Laboratory Strains of Delia (= Hylemya) Antiqua Meigen

Using confined larval populations of Hylemya antiqua the effects of increasing larval density on larval dispersal, pupation and mortality were assessed. The experiments were performed initially using a laboratory strain (35 generations rearing in the laboratory). It was shown that dispersal, pupation and mortality were significantly different for the two strains with the wild strain dispersing at a much lower density level than the laboratory strain and with a significantly shorter mean dispersal time. The experiments were repeated four generations later to monitor the effects of laboratory colonization on the wild strain. This time dispersal, pupation and mortality were not significantly different for the two strains; the same was true for larval dispersal time. It was concluded that laboratory colonization had significantly altered larval dispersal behaviour in the wild strain. Multiple comparisons between all four strains revealed that larval dispersal in the original wild strain was significantly different from that in the other three strains. The same pattern emerged following multiple comparisons of the mean larval dispersal times. Therefore, the two laboratory strains and the wild strain reared for a total of six generations in the laboratory exhibited identical responses to increasing larval density as measured by dispersal, pupation, mortality and dispersal time. It was further demonstrated that several self-regulatory mechanisms mitigating against the adverse effects of increasing larval density were present i.e. the magnitude of the dispersal process, the time at which dispersal occurred and regulation of pupal size. It was shown that these processes did not always operate concurrently and often exhibited some interactions. The results were discussed in the framework of laboratory adaptation of the wild strain and the relevance of these behavioural changes when such individuals would be released into a field population during genetic control procedures.

GENETIC CONTROL OF HYLEMYA ANTIQUA II: CAN INBREEDING DEPRESSION BE A SERIOUS OBSTACLE TO THE DEVELOPMENT OF HOMOZYGOUS REARRANGEMENT LINES?

In relation to the homozygosing of chromosomal translocations, eight control lines of Hylemya antiqua (Meigen) were maintained for three generations by full sib mating. During the course of inbreeding, several biological parameters were measured, namely egg, larval and pupal mortality, adult‐mating propensity and adult sex ratio. In five of the lines there was a significant reduction in egg hatchability. The egg, larval and pupal mortality data were converted to k values in order to illustrate the relative importance of these three developmental stages. Larval mortality was the most significant contributor to fitness reduction. There was a gradual divergence of the k values for these three parameters as inbreeding progressed. No effect of inbreeding on mating propensity or sex ratio was demonstrated.

Genetic control of Delia (Hylemya) antiqua—VI. X-irradiation of fertilized females to produce translocations

Abstract Delia antiqua -fertilized females were irradiated with different doses of X-rays for the induction of translocations for genetic control. Egg sterility, pupal survival and adult F 1 sex ratio in the progeny were measured weekly for 3 weeks. At the lowest radiation dose egg sterility increased with time; the converse was true at the higher dose. Pupal survival was negatively influenced by dose; adult F 1 sex ratio was biased in favour of males as the dose increased. Translocations were recovered in the F 1 s from all radiation levels except one but at a frequency equivalent or even lower to that obtained when only males were irradiated with the same dose. It was concluded that irradiation of fertilized females in D. antiqua does not provide a more efficient system for the isolation of translocations than does male irradiation alone.