The ecology of the swede midge, Contarinia nasturtii (Kieff.) (Diptera, Cecidomyiidae). I.—Life-history and influence of temperature and moisture on development

Abstract

The life-history of Contarinia nasturtii (Kieff.), a gall-forming pest of swedes, was investigated in northern England in 1958–60, particular attention being paid to the influence of temperature and moisture on development in the soil. Most of the observations were made under controlled conditions in the laboratory, although much of the material came from the field.The adults emerge from the soil, mate, and live 1–3 days. In laboratory conditions, each female developed about 95 eggs, laid in batches of 2–50 on the young leaves of the host plant, and produced 78·7±11·4 unisexual larval progeny. The eggs require moist conditions, and hatched according to temperature after 1–10 days at 30–10°C. The larvae fed for 7–21 days at 25–15°C., producing a gall.The full-grown larvae burrow into the soil. It was found that they either pupated in oval-shaped cocoons just below the surface, producing adults 10–48 days later (at 25–12°C.) or become dormant in spherical cocoons. At 32·5°C. the pupae died, and below 32·5°C. males developed faster than females by about 24 hours.Dormancy is caused either by diapause, in which case the larvae require prolonged chilling before development can be resumed, or by drought, in which case development is resumed immediately in response to wetting.The incidence of diapause increased regularly during the summer generations, probably in response to decreasing day-length, and the larvae tended to avoid diapause when placed in high temperatures (e.g., 25°C.). The firmness of diapause appeared to vary according to the conditions experienced by the feeding and full-grown larvae, but, in general, the larvae completed diapause development after 100 days at 2–5°C. followed by 30 days at 20–25°C., i.e., after exposure to conditions similar to those experienced by the diapause larvae during winter and spring.Dormancy due to drought (quiescence) affected both non-diapause and post-diapause larvae; the former became quiescent on entering dry soil (pF>3·5–4·0), and the latter remained inactive if kept in dry or even in moist soil (pF 3·4) after completing diapause. In both cases, the termination of dormancy occurred immediately in response to a thorough wetting of the soil. The larvae left their spherical cocoons, moved to the surface, re-entered the ground and pupated in oval cocoons as if entering the soil for the first time.Factors that delay pupation of C. nasturtii similarly delay the development of its Hymenopterous parasites and hence synchronise the emergence of the adult parasites with the host's feeding stage.

Impact of Soil Type, Moisture, and Depth on Swede Midge (Diptera: Cecidomyiidae) Pupation and Emergence

“…However, why extremes of soil moisture contents can effectively hamper C. nasturtii emergence is unclear. Readshaw (1966) reported that C. nasturtii larvae could remain quiescent (dormant) and construct spherical cocoons when entering dry sandy loam (8Ð15% moisture content) and peaty clay soil (Ϸ43% moisture content) until the soils were thoroughly wetted. However, after C. nasturtii larvae in plant material were placed on top of the dry soil in our study, we observed that C. nasturtii larvae could still enter the soil but wrapped themselves with dry soil particles and became immobilized, instead Days to Þrst Loamy Þne sand 11.4 Ϯ 0.4 aC 12.7 Ϯ 0.3 abBC 11 Ϯ 0.6 cdC 13.5 Ϯ 2.5 bcB 18.5 Ϯ 0.5 cA emergence of burrowing into the soil, and died on top of the soil.…”

“…Thygesen (1966) studied the emergence of C. nasturtii in different soil types and found emergence was markedly earlier in light sandy soil than in heavy clay. In addition, Readshaw (1966) reported that soil moisture could affect C. nasturtii emergence and even cause dormancy after mature larvae were placed in soil with three to four different moisture levels. Readshaw (1968) suggested that it may be possible to achieve satisfactory control of C. nasturtii by simple cultural procedures, such as burying pupae too deeply in the soil to permit successful emergence.…”

Will climate change be beneficial or detrimental to the invasive swede midge in North America? Contrasting predictions using climate projections from different general circulation models

“…Changing the precipitation or RH% had a much larger effect on the location of the bioclimatic envelope than altering the temperature values. This is not surprising because C. nasturtii is known to be sensitive to soil moisture (Readshaw, 1966). While precipitation and RH% are roughly substitutable, temperature and precipitation (or RH%) have an almost additive effect on the distribution of C. nasturtii, with little interaction between the variables (see Fig.…”

“…It is a key factor in the termination of diapause (Readshaw, 1966) and thus, adult emergence. We confirmed this conclusion in 'Climate factors affecting distribution' (see Fig.…”

“…Because the emergence of C. nasturtii is primarily related to soil moisture (Readshaw, 1966), we wanted to be sure that the large differences in predicted swede midge bioclimatic envelopes based on the two GCMs (Figs 2-4, 6), were not simply due to differences in the methods of calculation for the RH% values. To do this, we used Eqn (1) to generate RH% estimates for the HadCM3 and re-ran the BEM using the new values for RH%.…”