Progression of phosphine resistance in susceptible Tribolium castaneum (Herbst) populations under different immigration regimes and selection pressures

Abstract

Insecticide resistance is an escalating global issue for a wide variety of agriculturally important pests. The genetic basis and biochemical mechanisms of resistance are well characterized in some systems, but little is known about the ecological aspects of insecticide resistance. We therefore designed a laboratory experiment to quantify the progression of phosphine resistance in Tribolium castaneum populations subject to different immigration regimes and selection pressures. Mated resistant females were added to originally susceptible populations under two distinct migration rates, and in addition, half of the populations in each migration treatment were exposed to selection pressures from phosphine fumigation. The progression of phosphine resistance was assessed by screening beetles for the resistance allele at rph2. Phosphine resistance increased slowly in the low migration treatment and in the absence of selection, as expected. But at the higher migration rate, the increase in frequency of the resistance allele was lower than predicted. These outcomes result from the high levels of polyandry known in T. castaneum females in the laboratory, because most of the Generation 1 offspring (86%) were heterozygous for the rph2 allele, probably because resistant immigrant females mated again on arrival. Phosphine resistance was not fixed by fumigation as predicted, perhaps because susceptible gametes and eggs survived fumigation within resistant females. In terms of phosphine resistance progression in populations exposed to selection, the effect of fumigation negated the difference in migration rates. These results demonstrate how species‐specific traits relating to the mating system may shape the progression of insecticide resistance within populations, and they have broad implications for the management of phosphine resistance in T. castaneum in the field. ​We specify and discuss how these mating system attributes need to be accounted for when developing guidelines for resistance management.

Variation in Endosymbionts of Phosphine Resistant and Susceptible Key Stored Grain Insect Pests

“…For residual free treatment, fumigant phosphine is used which is readily available as aluminium phosphide (Celphos) in tablet form and is a cheap source of fumigation (Collins et al, 2001). However, lack of ideal airtight condition, increases the frequency of control failure thereby consequently, increasing the frequency of application which leads to the high selection pressure for phosphine resistance in stored grain insect pests in many countries including India (Rafter et al, 2017). That also produces heritable resistance in many stored grain insect pests in many countries including India (Choudry, 2000).…”

Characterisation of variables associated with the flight behaviour of the rust-red flour beetle (Tribolium castaneum)

“…Multiple mating increases the probability that an individual female will (regardless of her phosphine resistance status) transfer phosphine resistance genes to new populations (given a high enough frequency of phosphine resistance in the population). In addition, mated females from highly resistant populations migrating into susceptible populations can re-mate and not only produce fully resistant offspring but also susceptible heterozygotes (Rafter et al, 2017). Polyandry also has implications for the genetic diversity across the offspring of resistant resident females that survive fumigation.…”

“…Polyandry also has implications for the genetic diversity across the offspring of resistant resident females that survive fumigation. That is, sperm stored within such females should be screened from the effects of phosphine (including those sperm from phosphine susceptible males with which she may have mated) (Rafter et al, 2017). Once fumigation has been completed, the multiple-mated females will produce progeny of mixed resistance genotypes and that has the potential to influence the dynamics of resistance alleles in the population, something that needs consideration in the development of models of phosphine resistance.…”

“…Investigations of polyandry are typically laboratory based and focused on the consequences for individual reproductive fitness. But polyandry is widespread enough (Taylor et al, 2014) to suggest its occurrence should not be seen as an evolutionary paradox (Arnqvist & Nilsson, 2000), but an unavoidable consequence of sexual reproduction (Pizzari & Wedell, 2013), with significant consequences at the population level (Lumley et al, 2015;Michalczyk et al, 2011;Rafter et al, 2017). We designed field-based tests to explore the level and impact of polyandry, and so revisit the paradox.…”

“…Understanding the extent of polyandry in field populations is crucial to interpreting the spatial spread of resistance and its dynamics within localities (where beetles settle). Multiple mating has been demonstrated to alter substantially the rate at which insecticide resistance spreads, whether within populations or spatially across discontinuous resources (Rafter et al, 2017;Blanco et al, 2010).…”