Stored alcohol and fatty acid intermediates and the biosynthesis of sex pheromone aldehyde in the moth Chloridea virescens.

In most species of moths, the female produces and releases a volatile sex pheromone from a specific gland to attract a mate. Biosynthesis of the most common type of moth sex pheromone component (Type 1) involves de novo synthesis of hexadecanoate (16:Acyl), followed by modification to various fatty acyl intermediates, then reduction to a primary alcohol, which may be acetylated or oxidized to produce an acetate ester or aldehyde, respectively. Our previous work on the moth Chloridea virescens (Noctuidae) showed that females produce 90% of the major pheromone component, (Z)-11-hexadecenal (Z11-16:Ald), via a direct and rapid route of de novo biosynthesis with highly labile intermediates, and ca. 10% from an indirect route that likely mobilizes a pre-synthesized 16-carbon skeleton, possibly, (Z)-11-hexadecenoate (Z11-16:Acyl) or hexadecanoate (16:Acyl). In this paper, we use stable isotope tracer/tracee techniques to study the dynamics of the precursor alcohol (Z)-11-hexadecenol (Z11-16:OH) and stores of Z11-16:Acyl and 16:Acyl to determine their roles in biosynthesis of Z11-16:Ald. We found: (i) that intracellular Z11-16:OH is synthesized at roughly the same rate as Z11-16:Ald, indicating that translocation and oxidation of this moiety does not rate limit biosynthesis of Z11-16:Ald, (ii) intracellular Z11-16:OH consists of two pools, a highly labile one rapidly translocated out of the cell and converted to Z11-16:Ald, and a less labile one that mostly remains in gland cells, (iii) during pheromone biosynthesis, net stores of Z11-16:Acyl increase, suggesting it is not the source of Z11-16:Ald produced by the indirect route, and (iv) no evidence for the gland synthesizing stored 16:Acyl prior to (up to 2 days before eclosion), or after, synthesis of pheromone commenced, suggesting the bulk of this stored moiety is synthesized elsewhere and transported to the gland prior to gland maturation. Thus, the pheromone gland of C. virescens produces very little stored fat over its functional lifetime, being optimized to produce sex pheromone.

Reinvestigation of sex pheromone biosynthesis in the moth Trichoplusiani reveals novel quantitative control mechanisms.

Many species of moths have a common control mechanism for synthesizing sex pheromone: the circadian release of pheromone biosynthesis-activation neuropeptide (PBAN) that switches pheromone synthesis on/off during the day. One apparent exception to this is the noctuid moth Trichoplusia ni (Hübner), in which pheromone synthesis appears continuous through the photoperiod, with circadian release of PBAN controlling emission rate of pheromone during calling. Sex pheromone biosynthesis was reinvestigated in T. ni using stable isotope tracer-tracee and gland sampling techniques to ascertain how pheromone quantities in gland cells and on the gland cuticular surface varied and were controlled. It was found that (i) carbohydrate from adult female feeding is used to synthesize sex pheromone, (ii) most of the stored acetate ester pheromone component(s) is contained in gland cells, (iii) a large pool of pheromone is synthesized and stored through the photoperiod with a slow turnover rate, (iv) although pheromone is synthesized throughout the photoperiod, its rate can vary, influenced by release of PBAN and possibly by an unidentified head factor, with both affecting carbohydrate uptake into the acetyl CoA pheromone precursor pool, and (v) as suggested previously, PBAN also influences translocation of pheromone out of the cell to the cuticular surface, possibly by causing breakdown of intracellular lipid droplets storing pheromone molecules. This work suggests that the quantitative synthesis and emission of pheromone in T. ni, and possibly other moths, is regulated by multiple complementary biochemical mechanisms.

Some Factors Influencing Calling Behavior and Mass Emission Rate of Sex Pheromone from the Gland of the Moth Chloridea virescens.

To attract a mate, females of most moth species synthesize and emit sex pheromone from a specific gland in a behavior termed "calling". In a broad temporal sense, calling behavior and pheromone synthesis are synchronized through the overlap of their circadian rhythms. However, the limited amount of pheromone a female produces each day must be managed so that pheromone is emitted at a sufficient (to attract males) mass emission rate (MER) over the entire calling period, typically many hours. We are studying pheromone synthesis and emission in the moth Chloridea (formerly Heliothis) virescens (family Noctuidae). One way that female C. virescens manage pheromone over their calling period is by calling intermittently; the period between calling bouts allows females to replenish pheromone, and resume calling at high MERs. However, militating against replenishment is loss of pheromone through putative catabolism. In this paper, we examined three aspects pertaining to pheromone MER in C. virescens: (i) the effect of adult feeding on calling behavior, (ii) the effect of certain behavioral/physical parameters on MER, and (iii) the relative loss (putative catabolism) of pheromone in retracted (non-calling) and everted (calling) glands. We found that (i) adult feeding increases calling duration, consistent with the known concomitant increase in pheromone production, (ii) various physical factors relating to the gland, including degree of eversion (surface area), orientation to airstream, and air velocity over the gland influence MER, and (iii) putative catabolism occurs in both retracted and everted glands, but substantially less pheromone is lost in the everted gland primarily because of the high MER when the gland is first everted. Together, these data demonstrate that, over the calling period, the efficient use of pheromone for emission by female C. virescens is dependent on the interaction among synthesis, storage, catabolism, and calling behavior.

Sex pheromone biosynthesis, storage and release in a female moth: making a little go a long way.

Moth pheromone research has pioneered much of our understanding of long-distance chemical communication. Two important characteristics of this communication have, however, remained largely unaddressed: the release of small quantities of pheromone by most moth species, despite potential advantages of releasing greater amounts, and the intermittency of release in some species, limiting the time of mate attraction. We addressed the proximate mechanisms underlying these characteristics by manipulating biosynthesis, storage and release of pheromone in females of the noctuid moth Chloridea virescens. We found that (i) mass release is determined by pheromone mass on the gland surface; (ii) amounts synthesized are limited by pheromone biosynthesis activating neuropeptide concentration, not precursor availability; (iii) some gland structural feature limits mass release rate; (iv) intermittent calling enables release at a mass rate greater than biosynthetic rate; and (v) at typical mass release rates, the periodicity of pheromone availability on the gland surface roughly matches the periodicity (intermittency) of calling. We conclude that mass release in C. virescens and possibly many other species is low because of constraints on biosynthesis, storage and gland structure. Further, it appears the behaviour of intermittent calling in C. virescens may have evolved as a co-adaptation with pheromone availability, allowing females to release pheromone intermittently at higher mass rates than the biosynthesis rate.

Investigating the status of pyrethroid resistance in UK populations of the cabbage stem flea beetle (Psylliodes chrysocephala).

The cabbage stem flea beetle, Psylliodes chrysocephala L. is a major pest of winter oilseed rape in several European countries. Traditionally, neonicotinoid and pyrethroid insecticides have been widely used for control of P. chrysocephala, but in recent years, following the withdrawal of neonicotinoid insecticide seed treatments, control failures have occurred due to an over reliance on pyrethroids. In line with previous surveys, UK populations of P. chrysocephala were found to exhibit high levels of resistance to the pyrethroid lambda-cyhalothrin. This resistance was suppressed by pre-treatment with the cytochrome P450 inhibitor PBO under laboratory conditions, suggesting that the resistance has a strong metabolic component. The L1014F (kdr) mutation in the voltage-gated sodium channel, which confers relatively low levels (10-20 fold) of resistance to pyrethroids, was also found to be widespread across the UK regions sampled, whereas the L925I (s-kdr) mutation was much less common. The current survey also suggests that higher levels of pyrethroid resistance have spread to the North and West of England, and that resistance levels continue to remain high in the South East.

The Effect of Pheromone Synthesis and Gland Retraction on Translocation and Dynamics of Pheromone Release in the Moth Chloridea virescens.

Most species of moths use a female-produced sex pheromone to bring mates together. Typically, sex pheromone is synthesized in a specialized gland and released during the behavior of "calling", in which the ovipositor and gland are extruded, allowing pheromone to evaporate. Although there has been much study on how a gland makes specific pheromone components, we know relatively little about how it actually functions with regard to synthesis, storage and release. In this paper, we investigated three aspects of gland function in the noctuid moth Chloridea virescens (Fabricius): (i) whether translocation of pheromone from site of synthesis to release is dependent on calling or ovipositor movement, (ii) whether pheromone synthesis rate limits release and (iii) how intermittent calling (observed in this and other species) might affect the dynamics of release rate. Firstly, by manipulating the gland to simulate calling (extruded) or non-calling (retracted), we showed that pheromone translocation occurred regardless of whether the gland was retracted or extruded. Secondly, by manipulating pheromone production, we found that females that produced more pheromone had higher release rates. It was especially noticeable that females had a higher release rate at the start of calling, which dropped rapidly and leveled off over time. Together, these data suggest that intermittent calling in C. virescens (and other species) may function to allow females to replenish pheromone stores on the gland surface between calling bouts, so that brief, high release rates occur at the start of a calling bout; thus, potentially increasing a female's chances of attracting a mate.

Calling Behavior and Sex Pheromone Release and Storage in the Moth Chloridea virescens.

Female moths release sex pheromone to attract mates. In most species, sex pheromone is produced in, and released from, a specific gland. In a previous study, we used empirical data and compartmental modeling to account for the major pheromone gland processes of female Chloridea virescens: synthesis, storage, catabolism and release; we found that females released little (20-30%) of their pheromone, with most catabolized. The recent publication of a new pheromone collection method led us to reinvestigate pheromone release and catabolism in C. virescens on the basis that our original study might have underestimated release rate (thereby overestimating catabolism) due to methodology and females not calling (releasing) continuously. Further we wished to compare pheromone storage/catabolism between calling and non-calling females. First, we observed calling intermittency of females. Then, using decapitated females, we used the new collection method, along with compartmental modeling, gland sampling and stable isotope labeling, to determine differences in pheromone release, catabolism and storage between (forced) simulated calling and non-calling females. We found, (i) intact 1 d females call intermittently; (ii) pheromone is released at a higher rate than previously determined, with simulations estimating that continuously calling females release ca. 70% of their pheromone (only 30% catabolized); (iii) extension (calling)/retraction of the ovipositor is a highly effective "on/off' mechanism for release; (iv) both calling and non-calling females store most pheromone on or near the gland surface, but calling females catabolize less pheromone; (v) females are capable of producing and releasing pheromone very rapidly. Thus, not only is the moth pheromone gland efficient, in terms of the proportion of pheromone released Vs. catabolized, but it is highly effective at shutting on/off a high flux of pheromone for release.

Production and Distribution of Aldehyde and Alcohol Sex Pheromone Components in the Pheromone Gland of Females of the Moth Chloridea virescens.

Aldehydes are components of many moth sex pheromones, and are thought to be produced from analogous alcohols by oxidase(s) in the cell membrane or the gland cuticle. This implies that the two types of components are produced and/or stored in different parts of the gland: alcohols in cells and aldehydes in cuticle. Few studies have investigated the distribution of components in moth pheromone glands. Using rinse/extract sampling, stable isotope tracer/tracee methods, and decapitation/ pheromone biosynthesis activating neuropeptide stimulation, we studied production and distribution of (Z)-11-hexadecenal (Z11-16:Ald) and (Z)-hexadecenol (Z11-16:OH) in the gland of Chloridea virescens (formerly Heliothis virescens). The rinse, which likely sampled the surface and outer cuticle, contained large amounts of aldehyde and small amounts of alcohol. By contrast, the residual extract, which likely sampled cells and less solvent-accessible (inner) cuticle, had large amounts of alcohol and small amounts of aldehyde. When a tracer (U-13C-glucose) was fed to females, the aldehyde had higher isotopic enrichment than the alcohol in the rinse, but not in the residual extract, showing that in the rinse pool, Z11-16:Ald was, on average, synthesized before Z11-16:OH. This is consistent with greater aldehyde than alcohol flux through the cuticle. While our results are consistent with cell/cuticle synthesis sites for alcohol/aldehyde components, we cannot rule out both being synthesized in gland cells. We propose two alternative conceptual models for how site of production, cuticular transport and catabolism/metabolism might explain the relative masses of Z11-16:Ald and Z11-16:OH translocated to the pheromone gland surface in female C. virescens.

The Dynamics of Pheromone Gland Synthesis and Release: a Paradigm Shift for Understanding Sex Pheromone Quantity in Female Moths.

Moths are exemplars of chemical communication, especially with regard to specificity and the minute amounts they use. Yet, little is known about how females manage synthesis and storage of pheromone to maintain release rates attractive to conspecific males and why such small amounts are used. We developed, for the first time, a quantitative model, based on an extensive empirical data set, describing the dynamical relationship among synthesis, storage (titer) and release of pheromone over time in a moth (Heliothis virescens). The model is compartmental, with one major state variable (titer), one time-varying (synthesis), and two constant (catabolism and release) rates. The model was a good fit, suggesting it accounted for the major processes. Overall, we found the relatively small amounts of pheromone stored and released were largely a function of high catabolism rather than a low rate of synthesis. A paradigm shift may be necessary to understand the low amounts released by female moths, away from the small quantities synthesized to the (relatively) large amounts catabolized. Future research on pheromone quantity should focus on structural and physicochemical processes that limit storage and release rate quantities. To our knowledge, this is the first time that pheromone gland function has been modeled for any animal.

Differential Pheromone Sampling of the Gland of Female Heliothis Virescens Moths Reveals Glandular Differences in Composition and Quantity.

By differentially sampling the pheromone gland of females of the moth Heliothis virescens, we explored differences in pheromone on the surface, or outer distal layer(s) of the gland, and that located more proximally. For this, we used two sampling approaches, (i) a solid phase microextraction fiber rub followed by solvent extraction of residual pheromone (SPME rub/extract), and (ii) rapid solvent rinsing followed by solvent extraction of residual pheromone (rinse/extract). The SPME rub showed differences in component ratio between the dorsal and ventral gland surfaces. The rinse sampled a greater amount of pheromone than the SPME rub, sampling the whole gland surface as well as likely deeper into the gland. Compared to the other samplings, pheromone in the rinse was depleted in the minor component; consequently, the corresponding residual extract was highly enriched in the minor component. Further rinses of the gland yielded only small amounts of pheromone, with a similar component ratio as the first rinse, suggesting that the residual pheromone was less accessible and required extraction in solvent to be liberated. Sampling over the photoperiod showed that the more volatile minor component was depleted (relative to the major component) on the surface/outer cuticle over the period when females called. Together, these data suggest that the pheromone is stored, at least in part, on and in the gland cuticle and that distinct pools may be transported to different topographic regions. Females fed with a stable isotope tracer, incorporated label into pheromone in the gland very rapidly, with the labeled pheromone appearing on the gland surface ca. 1 min later.

Sex pheromone in the moth Heliothis virescens is produced as a mixture of two pools: de novo and via precursor storage in glycerolipids.

Most species of moths use a female-produced volatile sex pheromone, typically produced via de novo fatty acid synthesis in a specialized gland, for communication among mates. While de novo biosynthesis of pheromone (DNP) is rapid, suggesting transient precursor acids, substantial amounts of pheromone precursor (and other) acids are stored, predominantly in triacylglycerols in the pheromone gland. Whether these stored acids are converted to pheromone later or not has been the subject of some debate. Using a tracer/tracee approach, in which we fed female Heliothis virescens U-13C-glucose, we were able to distinguish two pools of pheromone, in which precursors were temporally separated (after and before feeding on labeled glucose): DNP synthesized from a mixed tracer/tracee acetyl CoA pool after feeding, and pheromone made from precursor acids primarily synthesized before feeding, which we call recycled precursor fat pheromone (RPP). DNP titer varied from high (during scotophase) to low (photophase) and with presence/absence of pheromone biosynthesis activating neuropeptide (PBAN), in accord with native pheromone titer previously observed. By contrast, RPP was constant throughout the photoperiod and did not change with PBAN presence/absence. The amount of RPP (6.3-10.3 ng/female) was typically much lower than that of DNP, especially during the scotophase (peak DNP, 105 ng/female). We propose an integral role for stored fats in pheromone biosynthesis, in which they are hydrolyzed and re-esterified throughout the photoperiod, with a small proportion of liberated precursor acyl CoAs being converted to pheromone. During the sexually active period, release of PBAN results in increased flux of glucose (from trehalose) and hydrolyzed acids entering the mitochondria, producing acetyl CoA precursor for de novo fat and pheromone biosynthesis.

Incidence, Spread and Mechanisms of Pyrethroid Resistance in European Populations of the Cabbage Stem Flea Beetle, Psylliodes chrysocephala L. (Coleoptera: Chrysomelidae).

BACKGROUND: Cabbage stem flea beetle (CSFB), Psylliodes chrysocephala L. (Coleoptera: Chrysomelidae) is a major early season pest of oilseed rape throughout Europe. Pyrethroids have been used for controlling this pest by foliar application, but in recent years control failures have occurred, particularly in Germany due to the evolution of knock-down resistance (kdr). The purpose of this study was to investigate the incidence and spread of pyrethroid resistance in CSFB collected in Germany, Denmark and the United Kingdom during 2014. The level of pyrethroid resistance was measured in adult vial tests and linked to the presence of kdr genotypes. RESULTS: Although kdr (L1014F) genotypes are present in all three countries, marked differences in pyrethroid efficacy were found in adult vial tests. Whereas Danish CSFB samples were in general susceptible to recommended label rates, those collected in the UK mostly resist such rates to some extent. Moderately resistant and susceptible samples were found in Germany. Interestingly, some of the resistant samples from the UK did not carry the kdr allele, which is in contrast to German CSFB. Pre-treatment with PBO, prior to exposure to λ-cyhalothrin suggested involvement of metabolic resistance in UK samples. CONCLUSION: Danish samples were mostly susceptible with very low resistance ratios, while most other samples showed reduced sensitivity in varying degrees. Likewise, there was a clear difference in the presence of the kdr mutation between the three countries. In the UK, the presence of kdr genotypes did not always correlate well with resistant phenotypes. This appears to be primarily conferred by a yet undisclosed, metabolic-based mechanism. Nevertheless our survey disclosed an alarming trend concerning the incidence and spread of CSFB resistance to pyrethroids, which is likely to have negative impacts on oilseed production in affected regions due to the lack of alternative modes of action for resistance management purposes.

Sex pheromones in mate assessment: analysis of nutrient cost of sex pheromone production by females of the moth Heliothis virescens.

It has been postulated that sex pheromones, in addition to their role in mate recognition and/or finding, may also serve a role in assessment of mate quality. For this, a sex pheromone must give honest information about a signaler's quality, with honesty ensured by a direct metabolic or indirect fitness cost to the signaler. Using a stable isotope tracer-tracee method, we characterized the nutrient pools that fuel sex pheromone production in females of the moth Heliothis virescens, as well as the relative importance of larval- and adult-acquired nutrients to this process. Females used three pools for de novo biosynthesis of sex pheromone, hemolymph trehalose, glycogen (via trehalose) and fat, and produced ca. 25% of pheromone directly from stored (previously synthesized) precursor fatty acids. Pheromone was produced roughly equally from carbohydrate and fat. Adult feeding was very important for pheromone biosynthesis, with a maximum of 65% of de novo biosynthesized pheromone produced from a single adult feed (carbohydrate). Although these nutrient pools are shared with other reproductive physiologies, notably oocyte production, it is unlikely that pheromone production imposes a significant metabolic cost on females, because (i) the amount of nutrients used for pheromone production is negligible compared with that available, (ii) the hemolymph trehalose pool is readily replaceable throughout the adult life, and (iii) in mated females, carbohydrate shortages result in reduced allocation to pheromone.

The evolution of insecticide resistance in the peach potato aphid, Myzus persicae.

The peach potato aphid, Myzus persicae is a globally distributed crop pest with a host range of over 400 species including many economically important crop plants. The intensive use of insecticides to control this species over many years has led to populations that are now resistant to several classes of insecticide. Work spanning over 40 years has shown that M. persicae has a remarkable ability to evolve mechanisms that avoid or overcome the toxic effect of insecticides with at least seven independent mechanisms of resistance described in this species to date. The array of novel resistance mechanisms, including several 'first examples', that have evolved in this species represents an important case study for the evolution of insecticide resistance and also rapid adaptive change in insects more generally. In this review we summarise the biochemical and molecular mechanisms underlying resistance in M. persicae and the insights study of this topic has provided on how resistance evolves, the selectivity of insecticides, and the link between resistance and host plant adaptation.

Increased allocation of adult-acquired carbohydrate to egg production results in its decreased allocation to sex pheromone production in mated females of the moth Heliothis virescens.

Females of most species of moths produce a volatile sex pheromone that attracts conspecific males over distance. In females of the polyandrous moth Heliothis virescens, feeding on carbohydrate (e.g. nectar) supplies precursor, via hemolymph trehalose, for both sex pheromone and egg production. With limited carbohydrate acquisition these two reproductive physiologies might compete for hemolymph trehalose, resulting in an allocation deficit to either sex pheromone or egg production. Using virgin and mated females, which have low and high egg maturation rates, respectively, we fed females a limited diet of (13)C-labeled glucose daily and, using mass isotopomer distribution analysis, determined allocations of adult-acquired carbohydrate (AAC) to newly synthesized pheromone and ovarian and egg fats, our proxies for allocation to egg production. With increased number of feeds, AAC enrichment of hemolymph trehalose increased, as expected. This led to mated females increasing their proportional allocation of AAC to ovarian and egg fats, but decreasing their proportional allocation of AAC to pheromone production. By contrast, virgins increased their proportional allocation of AAC to pheromone production with increased feeds, consistent with increasing AAC enrichment of hemolymph trehalose. These results show that with limited AAC intake, enhanced egg maturation in mated females results in reduced AAC allocation to pheromone production; this does not occur in virgins because of their lower egg maturation rate. This physiological competition for AAC corresponded with decreased pheromone production in mated moths to levels unlikely to attract mates. Therefore, the availability and/or allocation of AAC may be a proximate mechanism underlying the incidence of polyandry in this and other species of moths.

A mutation (L1014F) in the voltage-gated sodium channel of the grain aphid, Sitobion avenae, is associated with resistance to pyrethroid insecticides.

BACKGROUND: The grain aphid, Sitobion avenae Fabricius (Hemiptera: Aphididae), is an important pest of cereal crops. Pesticides are the main method for control but carry the risk of selecting for resistance. In response to reports of reduced efficacy of pyrethroid sprays applied to S. avenae, field samples were collected and screened for mutations in the voltage-gated sodium channel, the primary target site for pyrethroids. Aphid mobility and mortality to lambda-cyhalothrin were measured in coated glass vial bioassays. RESULTS: A single amino acid substitution (L1014F) was identified in the domain IIS6 segment of the sodium channel from the S. avenae samples exhibiting reduced pyrethroid efficacy. Bioassays on aphids heterozygous for the kdr mutation (SR) or homozygous for the wild-type allele (SS) showed that those carrying the mutation had significantly lower susceptibility to lambda-cyhalothrin. CONCLUSION: The L1014F (kdr) mutation, known to confer pyrethroid resistance in many insect pests, has been identified for the first time in S. avenae. Clonal lines heterozygous for the mutation showed 35-40-fold resistance to lambda-cyhalothrin in laboratory bioassays, consistent with the reported effect of this mutation on pyrethroid sensitivity in other aphid species.

Ovipositional preference and larval performance of the banded sunflower moth (Lepidoptera: Tortricidae) and its larval parasitoids on resistant and susceptible lines of sunflower (Asterales: Asteraceae).

Banded sunflower moth, Cochylis hospes Walsingham, is one of the most destructive seed-feeding insect pests of sunflowers, causing significant economic yield losses in the northern Great Plains. In an attempt to understand host-plant resistance mechanisms for this pest, we field-tested, over several years, the effects of seven sunflower accessions, rated as resistant to C. hospes in previous screening trials, and a susceptible control (Par 1673-2), on the ovipositional preference and larval performance of C. hospes and its larval parasitoids. Of the resistant accessions, PI 494859 was the most preferred for oviposition, receiving a significantly greater number of eggs per head than did the susceptible Par 1673-2 in 2 of 3 yr. However, the numbers of larvae, and consequently the rate of seed infestation, found in PI 494859 heads were significantly lower than those in Par 1673-2 heads over all 3 yr. Female moths laid relatively few eggs on accessions PI 170385, 291403, and 251902, compared with on Par 1673-2, resulting in lower numbers of larvae per head and lower percentages of seed damaged. No association was observed between the concentrations of two diterpenoid alcohols or two diterpenoid acids in sunflower bracts and the numbers of eggs laid on the heads of the accessions. The number of banded sunflower moth larvae and the proportion of seeds damaged were positively correlated with kaurenoic acid concentrations and negatively correlated with kauranol concentrations. A positive association between resistance to larval feeding and parasitism was found in years 2006 and 2008, with resistant accessions having significantly greater proportions of parasitized larvae than did the susceptible Par 1673-2.

Permeability barriers to embryo cryopreservation of Pectinophora gossypiella (Lepidoptera: Gelechiidae).

The aim of this study was to develop a method to cryopreserve the embryos of the pink bollworm moth, Pectinophora gossypiella (Saunders). Previously developed dipteran cryopreservation protocols were not directly adaptable to use with the embryos of this lepidopteran species. Physiochemical and electron microscope observations revealed substantial differences in the structure of the chorion, wax layer, and vitelline membrane complex when comparing the cryopreservable embryonic stages of P. gossypiella and dipteran embryos. Thus, the initial steps dealing with dechorionation and permeabilization were ineffective and had to be altered. Exposure to the sodium hypochlorite-based chorion removal step decreased P. gossypiella embryo viability to a very low level. Survival increased and permeability was evident when an alkane wash was used as the first step in the procedure. After the alkane treatment with a surfactant yielded the maximum exchange of cryoprotectant with water as evidenced by a significant lowering of the supercooling point of the cryoprotectant-loaded embryos. The remainder of the cryopreservation and storage recovery protocol for P. gossypiella was similar to those developed for dipteran embryos. Survival of recovered, hatched embryos to adulthood was approximately 7%.

Survey of resistance to four insecticides and their associated mechanisms in different genotypes of the green peach aphid (Hemiptera: Aphididae) from Chile.

The green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae) is amajor pest of agriculture worldwide that has proved to be particularly adept at evolving insecticide resistance. Several mechanisms that confer resistance to many insecticide types have been described in M. persicae. We measured the resistance status of nine multilocus genotypes (MLGs) of this aphid species collected in Chile. MLGs were identified using microsatellite markers, and these MLG clonal populations were measured for the presence of modified acetylcholinesterase (MACE), kdr and super kdr mutations, and enhanced carboxyl esterase activity. Toxicological bioassays were used to estimate aphid LC50 when treated with metamidophos (organophosphate), pirimicarb (dimethyl carbamate), cyfluthrin (pyrethroid), and imidacloprid (neonicotinoid). Two MLGs presented >20-fold resistance to pirimicarb, which was associated with the MACE mutation in the heterozygous condition. The kdr mutation was found in only four MLGs in the heterozygous condition and they showed resistance ratios (RR) to cyfluthrin of less than sevenfold. The super kdr mutation was not detected. Enhanced carboxyl esterase activity was predominantly found in the susceptible (S) to first level of resistance (R1) with RR to metamidophos less than eight-fold. Finally, RR to imidacloprid was also less than eight-fold in all MLGs tested. A few MLGs with resistance to pirimicarb were found, while susceptibility to cyfluthrin, metamidophos and imidacloprid was still predominant. A significant positive correlation between imidacloprid tolerance with pirimicarb resistance was detected, as well as between imidacloprid and metamidophos tolerance. With the increase in the use of neonicotinoid insecticides, better rotation of insecticides with different modes of action will be necessary to prevent further development of M. persicae insecticide resistance in Chile.

Can invasions occur without change? A comparison of G-matrices and selection in the peach-potato aphid, Myzus persicae.

Most evolutionary research on biological invasions has focused on changes seen between the native and invaded range for a particular species. However, it is likely that species that live in human-modified habitats in their native range might have evolved specific adaptations to those environments, which increase the likelihood of establishment and spread in similar human-altered environments. From a quantitative genetic perspective, this hypothesis suggests that both native and introduced populations should reside at or near the same adaptive peak. Therefore, we should observe no overall changes in the G (genetic variance-covariance) matrices between native and introduced ranges, and stabilizing selection on fitness-related traits in all populations. We tested these predictions comparing three populations of the worldwide pest Myzus persicae from the Middle East (native range) and the UK and Chile (separately introduced ranges). In general, our results provide mixed support for this idea, but further comparisons of other species are needed. In particular, we found that there has been some limited evolution in the studied traits, with the Middle East population differing from the UK and Chilean populations. This was reflected in the structure of the G-matrices, in which Chile differed from both UK and Middle East populations. Furthermore, the amount of genetic variation was massively reduced in Chile in comparison with UK and Middle East populations. Finally, we found no detectable selection on any trait in the three populations, but clones from the introduced ranges started to reproduce later, were smaller, had smaller offspring, and had lower reproductive fitness than clones from the native range.