Sampling procedures and adult sex ratios in spruce budworm

Abstract

Unbiased estimates of sex ratios that reflect local abundance of adult insects are practically difficult to obtain because many gender‐specific behavioural adaptations differentially influence the catchability of males and females in commonly applied sampling procedures. Historic data on outbreak populations of spruce budworm, Choristoneura fumiferana Clemens (Lepidoptera: Tortricidae), the major pest of conifers in Nearctic boreal forests, include dozens of sex ratio observations for 10 different sampling procedures; these data illustrate the importance of understanding the reproductive ecology of adults to contextualize sex ratio assessments. Sex ratios of resident adults (assessed by rearing field‐collected pupae to adulthood or fogging host trees with insecticide) were not different from 1:1. Sex ratios of in‐flight adults collected using Malaise traps or light traps deployed in tree canopies were consistently male‐biased, which presumably reflects the higher level of flight activity for males relative to females. Sex ratios of moths captured outside the forest canopy (presumed migrants), in contrast, were consistently female‐biased, a trend which is expected because females seeking oviposition sites are more likely to undergo migration than are males. The sex ratio among adults that died from natural causes (collected on drop trays) was not distinguishable from 1:1. In pre‐outbreak (endemic) populations, sex ratios estimated by light trapping were much more strongly male‐biased than in outbreak populations. This surprising result should, however, be interpreted with caution because little is known of reproductive ecology in endemic budworm populations.

Survey tools and demographic parameters of SlovakianAgrilusassociated with beech and poplar

“…For example, the extreme variation in sex ratio observed between Agrilus spp. on detection traps is likely not due to variations in abundance of males and females in field populations but rather reflects systematic biases linked with different sampling procedures (Rhainds & Heard, 2015). In strict terms of detection (presence-absence data), however, the traps that captured the highest numbers of Agrilus (purple traps baited with cubeb oil for A. viridis, green traps for A. olivicolor and A. convexicollis) are most likely to detect potentially invasive species early in the invasion process (Allison & Redak, 2017).…”

Indirect host-mediated effects of an exotic phloem-sap feeder on a native defoliator of balsam fir

“…While thinning appeared to interact with gout to influence sex ratio, its effect was extremely subtle: we could detect no treatment effects on sex ratio when unthinned and thinned stands were analyzed separately, and all sex ratios were close to 1:1 (as expected for resident budworm populations; Rhainds and Heard, 2015). Thinning did interact with both budworm density and gout to influence budworm survivorship: survivorship declined with budworm density and with gout in unthinned stands, but not (significantly) in thinned ones.…”

Interguild interactions between a non‐native phloem feeder and a native outbreaking defoliator

“…Unbiased estimates of sex ratios for local populations are difficult to obtain because of gender‐specific behavioural differences that influence trap catch data. Sex ratios from multiple different sampling procedures were not markedly different from 1 : 1 (Miller, ; Rhainds & Heard, ; but see Graham, ), therefore, if we assume that approximately half our surviving population were females, we can infer fecundity. It has previously been shown that the potential fecundity of females from spruce trees increased by an average of 69 eggs for each 1‐mm increase in fore wing length (Thomas et al ., ).…”