Can intraspecific variation in an herbivorous mite alter responses to

21 22 The effects of drought stress on plants and phytophagous arthropods are topics currently extensively 23 investigated in the context of climate change. Dryness not only impacts cultivated plants but also 24 their parasites, which in some cases are favoured by drought. It represents a major challenge that 25 agriculture is facing in a perspective of intensification of drought. Direct effects of drought on 26 herbivorous arthropods typically produce bigger offspring and faster development but attractiveness 27 can also occur. However, how much responses to abiotic factors differ among populations of a 28 species remains poorly documented. The impact of drought-stressed plants on key life-history 29 parameters is here investigated for a major agricultural pest, the two spotted spider mite, 30 Tetranychus urticae, depending on the climatic conditions of the localities at origin. Sampled 31 localities represent a rather wide range of core climate conditions across the mite’s native 32 distribution area with contrasting climatic profiles, ranging from wet temperate to cool Atlantic 33 localities to medium to dry hot Mediterranean localities. Plant drought stress effects on mites was 34 estimated by measuring four life history traits: development time, fecundity, sex-ratio and 35 emigration rate in a common garden experiment made of two modalities: well-watered and drought36 stressed bean plants. Mites feeding on drought-stressed plants displayed shorter developmental 37 time and attempted to leave leaf patches less often, and young females were more fecund. The 38 mites originating from wet temperate to cool Atlantic localities respond more strongly to drought 39 than mites originating from medium to dry hot Mediterranean localities, suggesting local adaptation 40 of T. urticae populations to various aridity values and indicates that mite feeding behaviour is shaped 41 by the climatic conditions they faced in the area of origin. 42 43 44 Keyword 45 46 Acari; Tetranychus urticae; Europe; Mediterranean; local adaptation; common garden experiment; 47 life-history traits 48 49

Similarly, Takafuji et al. (1991) also in T. urticae and Suwa & Gotoh (2006) in Tetranychus pueraricola, 103 observed a South-North gradient in the diapause induction of these two species along the Japanese 104 archipelago. 105 106 Thus, intraspecific variation is common in many organisms. Drought stress also varies historically in 107 different geographic origins, and is becoming more common in some regions due to climate change 108 Here, we explore how drought stress in host plants affects different populations of an herbivorous 109 mite that is a major plant pest, the two spotted spider mite, T. urticae. This work focuses on if and 110 how responses depend on the geographic origin of the mites. 111

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The effect of plant drought stress on mites was estimated by measuring four life history traits in two 115 common garden experiments, each using well-watered and drought-stressed bean plants. We 116 measured development time of females (experiment I) and fecundity, leaving rates and sex ratio of 117 progeny (experiment II). Tetranychus urticae is an arrhenotokous mite, and sex ratio represents a way 118 to respond to changing environments (Crozier, 1985).  °C / 40 ± 30 % RH) for ten days after sowing. 160 Ten days after sowing, bean seedlings (two expanded seed leaves) were transferred to a climatic 161 chamber with diurnal (25 ± 0.5 °C) and nocturnal (23 ± 0.5 °C) temperatures and using a light cycle of 162 L/D 16/8 h. Plants were watered differentially according to treatment in the climatic chambers as 163 described below. Light was provided by agro red and blue LED lamps (Philipps Green Power LED). 164 Relative humidity was not regulated but limited using an air dehumidifier (Rexair 2500T, Rexair, 95330 165 Domont, France) and was 50 ± 20 % RH. Drought stress maintenance and assessment. After transferring bean seedlings from the greenhouse 173 to the climatic chamber, these continued to be exposed to two different water regimes: either well-174 watered or drought-stressed regime. These two modalities corresponded to soil moisture maintained 175 above 45% and between 10-8% (8% is over the wilting point), respectively. Plant watering was carried 176 out in two ways depending on the experiment: (1) in experiment I, all water regimes were ensured 177 using an automatically regulated drip irrigation system. Soil water content (RH) was measured using 5 178 moisture sensors (SM150 with GP2 Data Logger, Delta-T Devices Ltd, Cambridge, UK) in each watering 179 treatment and linked to DeltaLINK 3.1.1 PC software (Delta-T Devices Ltd, Cambridge, UK) for setting 180 up and downloading data from a GP2 station. In the well-watered treatment, when the average soil 181 moisture dropped to 45%, each plant was automatically watered for 30 seconds (delivering 17 ml of 182 water) by a drip. In the drought-stressed treatment, watering was activated (same duration and 183 amount of water per watering event) when soil moisture dropped to 8% (see Supplementary Figure 1  on the tape stripe to form a cord (that delimits a squared arena) that spider mites cannot cross. 221 Females placed in these arenas were allowed to lay eggs for 24 hours and then removed (Figure 2A for each trait and (3) between age of females (3 and 9 days old). When the ANOVA analyses between 298 watering regimes were significant, correlations were tested for the difference between water 299 regimes and each of the 20 climatic variables (19 Bioclimatic variables + Global Aridity Index). In the 300 same way, correlations were tested for non-stressed or drought-stressed traits' plant data when the   ANOVA conducted on development time data showed highly significant variation between the water 359 regimes (P < 0.001) but not between populations (Table 3). Thus we further only tested the 360 correlations between the differences of development time and the climatic variables of the locations. 361 We observed a positive correlation between the reduction in development time and Global Aridity 362 Index (see Table 4). The development time was shorter on drought-stressed plants and the reduction 363 increased for the mites originated from locations with high summer humidity (high Global Aridity 364 Index). In addition, a significant correlation was also observed for five others climatic variables (see 365

Fecundity 380
Life history traits variation in mite populations in response to host plant water regimes is summarised 381 in Figure 6.

Three-day-old females 394
For all but one population (CY-II), we observed an increase in the fecundity of females reared on 395 drought-stressed plants (Table 5) and it was significant for seven populations: FR-I, FR-III, FR-V, GR-I,  396 GR-II, IT-I and UK-I. The two ANOVA analyses performed with differences in fecundities observed 397 between water regimes and between mite populations, were significant (Table 3). Three sets of 398 correlations were subsequently tested with the climatic variables on sampling locations and the 399 differences of fecundity of three-day-old females, the values of fecundity three-day-old females 400 reared on drought-stressed plants and the values of fecundity three-day-old females reared on non-401 stressed plants. Significant correlations were observed for fecundity differences of three-day-old 402 females between water regimes and for fecundity of three-day-old females reared on drought-403 stressed plants. By contrast, none of the correlations were significant for fecundity of three-day-old 404 females reared on non-stressed plants. Three climatic variables (BIO01, BIO06 and BIO11) showing 405 significant correlations are the same for both (differences between water regimes and drought 406 stressed plants) and are related to temperature, especially winter temperatures (see Table 6) with an 407 increase in fecundity and with the difference of fecundity between the two water regimes for the 408 locations with colder temperatures (Figure 6). 409

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In summary, the fecundity of three-day-old females increased (Table 5)

Nine-day-old females 419
We observed a significant increase (Table 5)

Comparison between three-and nine-day-old fecundity 427
ANOVA analysis performed between fecundity of the two different age females (three-day-old and 428 nine-day-old) were significant ( Table 3). The nine-day-old females laid fewer eggs than the three-day-429 old females, for both non-stressed and drought-stressed plants. We also observed a correlation 430 between females reared on well-watered plants (three-day-old and nine-day-old, r 2 =0.395, p=0.029). 431

Three-day-old females 433
Although ten of the twelve populations studied showed a decrease in the leaving rate of females on 434 drought-stressed plants (Table 7), results were significant for only two of them (CY-I and FR-II). The 435 ANOVA analysis on differences in leaving rate of three-day-old females calculated between plant 436 water regimes was also significant (Table 3) and the average mite leaving rate was found to be 437 approximately twice lower on drought-stressed plants than on non-stressed ones. Subsequently, one 438 set of correlations was tested between the differences of leaving rate of three-day-old females and 439 the climatic variables. Only the correlation with the climatic variable BIO07 (Annual Temperature 440 Range) was significant. 441 442

Nine-day-old females 443
The leaving rate of nine-day-old females was generally higher for mites exposed to non-stressed 444 plants. From the twelve populations studied, eleven showed an increase in the leaving rate on non-445 stressed plants (Table 7), and four of them (FR-I, FR-II, FR-III, FR-V) were significant. The two ANOVA 446 analyses performed, one on differences calculated between plant water regimes and a second 447 between populations were significant (Table 3). On average, the leaving rate was twice lower on tested with the climatic variables and the differences calculated between plant water regimes of the 450 leaving rate of nine-day-old females, the values of the leaving rate of nine-day-old females reared on 451 non-stressed plants and the values of the leaving rate of nine-day-old females reared on drought-452 stressed plants. Significant correlations (Table 8) with climatic variables were observed for  453 differences between plant water regimes and for drought-stressed plants, while none of the tests 454 involving non-stressed plants were significant. Each of climatic variables BIO12, BIO14, BIO17, BIO18 455 and BIO19 were correlated with the differences between water regimes and also with the leaving 456 rate on non-stressed plants. These represent precipitations variables and all but one (BIO19) denote 457 to summer precipitation or dryness. Global Aridity Index and BIO16 were also correlated with the 458 differences calculated between water regimes. 459 460 As observed for the development time pattern, mites originating from the four most humid localities 461 (FR-I, FR-II, FR-III, and FR-V) showed higher differences between the two water regimes and in line 462 with this, the climatic variables related to precipitation and dryness were linked to the correlations 463 with differences in the two water regimes. 464 465

Comparison between three and nine-day-old females 466
ANOVA analysis between female mites from the two age groups showed significant differences for 467 mites reared on non-stressed plants only (Table 3). The leaving rate of nine-day-old females was 468 twice that of the three-day-old females. 469 470

4.1 Three-day-old females 475
Sex-ratio progeny showed significant differences between water regimes in four populations (Table  476 9). However, two of them corresponded to an increase (CY-II and FR-V) and two others (CY-I and SP-I) 477 to a decrease of male proportion. ANOVA analysis between populations showed significant 478 differences in this life trait (Table 3)

Nine-day-old females 489
A significant increase (Table 9)

Comparison between three and nine-day-old females 497
ANOVA comparing progeny sex ratio between the two different age females (three-day-old and nine-498 day-old) age showed significant differences for both, non-stressed and drought-stressed plants 499 regimes (Table 3). For the two water regimes the sex-ratio of nine-day-old female progeny was 500 lower, i.e. more males were produced by old females than by young females.  fecundity, the increase of the first ten days on drought-stressed plant was counterbalanced by a 553 decrease after ten days. Nevertheless, our experimental design did not allow us to observe such a 554 shift with females older than 9-day-old females. When mites were placed on well-watered tomatoes 555 plants, Alzate  Our study reveals changes in life-history traits of mites when exposed to feed on drought-stressed 572 plants, with a shortened development time and an increased fecundity along with a decrease of mite 573 dispersal. Importantly, not all mites tested responded equally but changes varied depending on the partially, explained by the climatic conditions in the sampled locations. Since all the females coming 576 from the different localities were reared under identical conditions in a common garden experiment, 577 it is reasonable to accept that observed variation resulted from genetic differentiation in the tested 578 populations. Mites originating from wet to cool localities (Alsace and Pays Basque) had seldom 579 experience of drought-stressed host plants while mites from Cyprus and Greece had to face harsh 580 climate and dryness half of the year. Previous studies (Chen et al., 2020) highlighted that genetic 581 variation for two closely related species Tetranychus truncatus and Tetranychus pueraricola, were 582 associated with climatic parameters, mainly temperature and precipitation across China. For both 583 species, genotype association was stronger with precipitation parameters together with the 584 neuropeptide receptor NPR-9 gene adjacent genomic region. The NPR-9 affects foraging behaviour 585 and nutrient storage (Bendena et al., 2015) and as a consequence development time and fecundity. 586 Literature tends then to support that local adaptation to diverse levels of aridity could shape mite 587 responses allowing them to adjust feeding behaviour in accordance with native local climatic 588 conditions and nutritional quality of the host plants. 589 590 Under a climate change scenario, it is expected that mites will experience harsher drought episodes 591 with environmental conditions leading to the selection of drought-adapted mites. In agricultural, in-592 tensification of damage in humid areas during the first years of drought (see Legrand et al., 2000 for 593 an example) will probably be limited by physiological costs but progressively lead to adaptation as 594 suggested by the mite responses in the driest areas of this study. These are important issues to be 595 taking into account for future strategies of pest management. 596 597