Flight ability and reproductive development in newly‐emerged pine weevil Hylobius abietis and the potential effects of climate change

Abstract

1 Adult pine weevils Hylobius abietis emerge from conifer root-stumps, on which larvae develop, over an extended period during summer and autumn. Newly-emerged weevils were tested for their ability to fly and assessed for wing muscle and reproductive development. In addition, the effect of summer-autumn maturation feeding on reproductive development was assessed in field bioassays. 2 There was considerable variation in development between newly-emerged weevils that was related to the timing of emergence. The first weevils, emerging in early July, weighed less than later-emerging ones, had undeveloped flight muscles and did not fly. Over the emergence period, wing muscle size and flight ability increased markedly, with 50-60% flying by mid-September. Differences between emerging adults are likely to have been affected by temporal changes in the quality of the bark on which the larvae feed. 3 Reproductive development lagged behind that of wing muscles but, in early August, there was a rapid increase in the proportion of weevils with immature eggs and a corresponding increase in oocyte size. However, although wing muscles were fully formed in later-emerging weevils, immature eggs were only approximately 10% of the volume of mature eggs. 4 In field bioassays of summer-autumn maturation feeding, eggs continued to develop and some weevils laid mature eggs. Feeding and development during the preoverwinter period is likely to influence winter survival and also dispersal and reproduction in the following spring. 5 The potential effects of climate change on the weevil life cycle are briefly discussed.Weevils are likely to benefit from the higher temperatures and later autumns predicted under climate change, resulting in an increase in damage to transplants.

The effect of temperature on the development and life cycle regulation of the pine weevil Hylobius abietis and the potential impacts of climate change

“…This variability could be maintained by a significant fitness advantage for weevils of first emergence in the autumn. Adults are reproductively immature when they emerge, and may also have undeveloped wing muscles (Nordenhem, 1989;Tan et al, 2010). Emergence and feeding during the autumn can therefore be important for the completion of wing muscle development and the initiation of egg development.…”

“…The weevils are predominantly semi-voltine, although the life cycle can vary from 1 year in the south to ≥4 years in northern forests and, at any one site, adult emergence may occur over ≥2 years (Bejer-Petersen et al, 1962;Bakke & Lekander, 1965;Bejer-Petersen, 1975;Moore et al, 2004). Adult-acquired resources are essential for reproduction, and probably also for wing muscle development (Örlander et al, 2000;Wainhouse et al, 2004;Tan et al, 2010) during 'maturation feeding'. Adult weevils typically emerge in the autumn to feed for a variable period before overwintering in the soil or litter layer and then re-emerging in the spring.…”

Interaction between flight, reproductive development and oviposition in the pine weevil Hylobius abietis

“…One notable difference between weevils from the pine and clearfell transects was that those from pine had well developed flight muscles from the beginning of the trapping period (mid‐April). Because many of these were likely to have entered the overwintering period with relatively well developed flight muscles after a period of autumn feeding (Tan et al , 2010), this suggests that weevils utilize reserves from stored fat rather than from the breakdown of wing muscles to survive over winter. It is possible, however, that some weevils feed on fine roots below ground during the winter (Örlander et al , 2001; Nordlander et al , 2003; Wallertz et al , 2006) or on twig material above ground on suitably warm days.…”

“…Before assay, up to 40 females each from the pine (range 6–40) and clearfell (range 1–33) transects at the overwintering site and up to 60 (range 7–60) at the oviposition sites were selected at random from each log trap collection date. Weevils were weighed and kept at 20–25 °C under bright artificial light (approximately 1 m below ten Sylvania F58W Gro‐lux T8 fluorescent tubes; Havells Sylvania Europe Ltd, Germany) for a minimum of 1 h. The method of flight testing was as described by Tan et al (2010). Briefly, individual weevils were suspended by a fine wire attached to the pronotum in a U‐shaped wind tunnel, open at the top and with an approximately laminar airflow of 1–2 m/s.…”

“…The main period of this ‘maturation’ feeding is, however, considered to occur in the spring after they re‐emerge, or after a main spring emergence. Although newly‐emerged weevils are generally flightless, those emerging in late autumn have much more well‐developed flight muscles than those that are among the first to emerge, and so have at least the potential for flight (Tan et al , 2010). Maturation feeding is necessary for egg development (Munro, 1928; Leather et al , 1999) and, for some weevils, is probably also important for the development of flight muscles (Nordenhem, 1989; Örlander et al , 2000).…”