Temperature, deltamethrin‐resistance status and performance measures of Plutella xylostella: complex responses of insects to environmental variables

Abstract

1. Worldwide, the excessive use of insecticides has resulted in field‐evolved insecticide‐resistant populations of diamondback moth (DBM), Plutella xylostella. A deltamethrin‐resistant DBM population from the field was divided into two subpopulations in the laboratory. One population (S‐strain) was maintained with no further exposure to insecticides, whereas the other population (R‐strain) was maintained under a regime of intermittent selection with deltamethrin. 2. Individuals from both strains were reared at constant temperatures in the range 10–35 °C in the absence of deltamethrin, and the effects of rearing temperature on various traits were investigated. At the time of experimentation, the R‐strain was 20‐fold more resistant to deltamethrin than the S‐strain. 3. Temperature differentially affected developmental time, adult life span, pupal weight, and fecundity of both strains. Although both strains laid eggs after being reared at 10 °C, few of these eggs were fertile. The R‐strain developed significantly faster than the S‐strain. The integrated performance of the S‐strain and R‐strain was greatest at 25 and 15 °C, respectively. 4. The present study provides important information on the complexities of the outcomes of the interactions between ectotherms and temperature. Specifically, temperature‐trait relationships may not be unimodal, and ectotherm genotypes (in this case insecticide‐resistance status) and abiotic stresses can interact with unpredictable outcomes. 5. Current models predicting DBM population dynamics and relative abundance in different locations do not consider different thermal biologies of different genotypes. The present study shows the dramatic effects of environment on many parameters used in these models and will help to enhance their accuracy, and thus their utility.

Differential temperature responses between Plutella xylostella and its specialist endo‐larval parasitoid Diadegma semiclausum—Implications for biological control

“…The parasitoid only arrested host development once the host entered the prepupal stage. Parasitized prepupae remained in that stage for much longer than the same stage of nonparasitized hosts after cocoon formation (Wang et al ., 2020), and they did not complete the pupal molt. At this time, parasitoid larvae within their hosts completed larval development and pupated.…”

“…Such an outcome could be the result of temperature-mediated responses of the host immune system (Strand & Pech, 1995;Fellowes et al, 1999), polyD-NAvirus expression (Lavine & Beckage, 1995;Webb, 1998;Huang et al, 2008;Etebari et al, 2011), and/or increased mortality of immature parasitoids due to high temperature exposure (Thomas & Blanford, 2003). Survival of nonparasitized P. xylostella was not affected by the rearing temperature (> 91% survival at all tempertaures tested in the range 10-30°C (Wang et al, 2020)), strongly suggesting that the higher mortality of immature parasitized hosts at 30°C is a consequence of the interaction between temperature and parasitism.…”

“…The effects of temperature on developmental traits and survival of the nonparasitized P. xylostella hosts of the same population were assessed in identical tests, but without exposure to parasitoids (Wang et al ., 2020). These data were used as controls to analyze the effects of parasitism by D. semiclausum , temperature, and interactions between these factors on parasitized hosts.…”

“…To directly assess the effects of thermal environment on the relative performance of a parasitoid and its host, we conducted detailed investigation of the interactions between the serious Brassica pest Plutella xylostella (Lepidoptera: Plutellidae) and its specialist, solitary endo‐larval koinobiont parasitoid Diadegma semiclausum (Hymenoptera: Ichneumonidae), which has been widely released as a classical biological control agent over the last 80 years (Furlong et al ., 2013). Experiments were explicitly designed to avoid most of the pitfalls described above and they were conducted over a wide range of constant temperatures known to extend across the critical bounds for host development (Liu et al ., 2002; Wang et al ., 2020). In the 1930s, D. semiclausum , collected in the north of England in the UK, were successfully introduced to control P. xylostella on the South Island of New Zealand (Hardy, 1938).…”

Influence of temperature on the development and reproduction of Cinara cedri (Hemiptera: Aphidoidea: Lachninae)

“…Temperature is one of the most important factors influencing most biological processes of insects, including their growth, development and reproduction (Clissold and Simpson, 2015; Cao et al ., 2018; Wang et al ., 2020). Generally, the developmental and reproductive rates of insects differ with temperature (Fand et al ., 2015; Krechemer and Foerster, 2015; Shi et al ., 2017).…”