Agna R.S. Rodrigues

Spinosad and the tomato borer Tuta absoluta: a bioinsecticide, an invasive pest threat, and high insecticide resistance.

The introduction of an agricultural pest species into a new environment is a potential threat to agroecosystems of the invaded area. The phytosanitary concern is even greater if the introduced pest’s phenotype expresses traits that will impair the management of that species. The invasive tomato borer, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), is one such species and the characterization of the insecticide resistance prevailing in the area of origin is important to guide management efforts in new areas of introduction. The spinosad is one the main insecticides currently used in Brazil for control of the tomato borer; Brazil is the likely source of the introduction of the tomato borer into Europe. For this reason, spinosad resistance in Brazilian populations of this species was characterized. Spinosad resistance has been reported in Brazilian field populations of this pest species, and one resistant population that was used in this study was subjected to an additional seven generations of selection for spinosad resistance reaching levels over 180,000-fold. Inheritance studies indicated that spinosad resistance is monogenic, incompletely recessive and autosomal with high heritability (h 2 = 0.71). Spinosad resistance was unstable without selection pressure with a negative rate of change in the resistance level ( = −0.51) indicating an associated adaptive cost. Esterases and cytochrome P450-dependent monooxygenases titration decreased with spinosad selection, indicating that these detoxification enzymes are not the underlying resistance mechanism. Furthermore, the cross-resistance spectrum was restricted to the insecticide spinetoram, another spinosyn, suggesting that altered target site may be the mechanism involved. Therefore, the suspension of spinosyn use against the tomato borer would be a useful component in spinosad resistance management for this species. Spinosad use against this species in introduced areas should be carefully monitored to prevent rapid selection of high levels of resistance and the potential for its spread to new areas.

Spermatogenesis, changes in reproductive structures, and time constraint associated with insemination in Podisus nigrispinus.

Males of the predatory stinkbug, Podisus nigrispinus (Dallas) (Hemiptera: Pentatomidae), accomplish long and multiple matings. We hypothesize that this behavior is due to time requirement for spermatozoa production and their transference to the females. Thus, this work investigated the effect of mating status of males and mating duration on spermatozoa transference to the females and the location of spermatozoa in the male reproductive tract during mating. On females, morphological alterations on female spermatheca and associated structures during a mating were investigated. Analyses of male reproductive tract showed presence of spermatozoa in the lumen of vas deferens was independent of mating status (ca. virgin, 0, 12 and 24 h after having a full mating), indicating continuous spermatogenesis which is supported by the absence of a seminal vesicle for spermatozoa storage. Female spermatheca had no changes associated with the duration of mating. However, females exhibited spermathecal elastic duct swelling by 30 min of mating duration. The success of males in filling the female spermatheca with spermatozoa depends on duration of mating. Thus, the results indicate that multiple mating is a requirement for reproductive success in the species by transference of spermatozoa and accessory substances stored in the female spermathecal duct. Likewise, the long mating is a male requirement to transfer materials in appropriate amount to the female but it is not dependent on spermatozoa alone.

Response of different populations of seven lady beetle species to lambda-cyhalothrin with record of resistance.

Simultaneous use of biological and chemical controls is a valued and historic goal of integrated pest management, but has rarely been achieved. One explanation for this failure may be the inadequate documentation of field populations of natural enemies for insecticide tolerance or resistance because natural enemies surviving insecticide application do not create problems like resistant pest species. Therefore, this study investigated 31 populations of lady beetles (Coleoptera: Coccinellidae) regarding their susceptibility to lambda-cyhalothrin, a pyrethroid insecticide that is widely used in cotton and other crops to control lepidopteran and coleopteran pests that are not targeted as prey by lady beetles. The study focused on seven coccinellid species common in cotton fields Coleomegilla maculata De Geer, Cycloneda sanguinea (L.), Eriopis connexa Germar, Harmonia axyridis (Pallas), Hippodamia convergens Guérin-Méneville, Olla v-nigrum (Mulsant), and Brumoides foudrasi (Mulsant) and one lady beetle species [Curinus coeruleus Mulsant] from a non-cotton ecosystem for comparisons. Dose-mortality curves were estimated after topical treatment of adult lady beetles with lambda-cyhalothrin. Statistically significant variations in lady beetle susceptibility were observed between species and between populations of a given species. Seven and eighteen populations of lady beetles exhibited greater values of LD50 and LD90, respectively, than the highest recommended field rate of lambda-cyhalothrin (20g a.i./hectare≈0.2g a.i./L) for cotton fields in Brazil. Furthermore, based on LD50 values, 29 out of 30 tested populations of lady beetles exhibited ratios of relative tolerance varying from 2- to 215-fold compared to the toxicity of lambda-cyhalothrin to the boll weevil, Anthonomus grandis Boh. (Coleoptera: Curculionidae). Four populations of E. connexa were 10.5-37.7 times more tolerant than the most susceptible population and thus were considered to be resistant to lambda-cyhalothrin, the first record of resistance for this species. These findings demonstrate that field selection for resistance to lambda-cyhalothrin in common lady beetles is occurring, opening up possibilities to effectively integrate biological control where the popular insecticide lambda-cyhalothrin is used.

Enzymes mediating resistance to lambda-cyhalothrin in Eriopis connexa (Coleoptera: Coccinellidae)

Resistance to widely used insecticide, lambda-cyhalothrin, was recently reported in the predatory lady beetle Eriopis connexa (Germar) (Coleoptera: Coccinellidae). However, to understand whether metabolic mechanisms underlie such resistance, synergism bioassays and in vitro studies were carried out by using inhibitors and model substrates for enzymatic assays, respectively. The LD50s estimated for susceptible and resistant populations ηg of lambda-cyhalothrin/insect, and thus, a 22-fold difference in resistance ratio. Synergism ratios for the susceptible population with piperonyl butoxide (PBO), diethyl maleate (DEM), triphenyl phosphate (TPP), and S,S,S-tributylphosphorotrithioate (DEF) were respectively 33.8-, 0.24-, 0.35-, and 4.25-fold, while for the resistant population, they were 1463.0-, 0.79-, 0.85-, and 282.6-fold, respectively. The synergized resistance ratios were 0.50-, 2.00-, 6.75-, and 8.77-fold with PBO, DEF, DEM, and TPP, respectively, while resistance was virtually suppressed with DEF. The esterase exhibited 4.16-, 4.03-, and 5.38-fold greater activity towards formation of α-naphthol, β-naphthol, and 4-nitrophenol in the resistant population of E. connexa than in the susceptible population. The activity of esterase depended on concentrations of DEF applied, either using α-naphthol or β-naphthol, which completely inhibited the activity at 636 ηM. The PBO inhibited the β-naphthol formation in approximately 50%, suggesting it as inhibitor of esterases. The activities of glutathione-S-transferase were similar and corresponded to 0.36-0.47 ηmol(-1) min(-1)μg of protein, for S and R populations, respectively. Similarly, the activities of cytochrome P450-dependent microsomal monooxygenases were 0.04 and 0.05 ηmol(-1) min(-1)μg of protein. The native gel indicated that the formation of β-naphthol was completely inhibited by methyl-paraoxon, but only partially inhibited by eserine, TPP, and PBO. Although other studies with DEF and PBO have demonstrated strong inhibition of type B carboxylesterase associated with insecticide resistance, the results reported here do not rule out metabolism by cytochrome P450-dependent microsomal monooxygenases as a factor conferring E. connexa resistance to lambda-cyhalothrin and confirmed that PBO may also act by inhibiting esterases of insects.

Life‐history costs associated with resistance to lambda‐cyhalothrin in the predatory ladybird beetle Eriopis connexa

1 The present study assessed the fitness of a lambda‐cyhalothrin‐resistant population of Eriopis connexa (Germar) with respect to development, reproduction, survival under prey scarcity and prey consumption. 2 Nontreated resistant females (R0) and females recovered after the topical application of 0.05, 0.10 and 0.25 mg active ingredient/mL of lambda‐cyhalothrin (R0.05, R0.10 and R0.25) produced, on average, 50% less eggs than susceptible females (S0), irrespective of the applied dose. All of the other traits evaluated remained similar. With respect to developmental characteristics, the larval viability and weight of adult male R0.25 progeny were statistically lower compared with the R0 and S0 progenies. Prey scarcity between days 3 and 13 of adulthood did not affect R0 and R0.25 survival, although egg production was significantly lower for R0 females, followed by R0.25 females, compared with S0 females. 3 The mean consumption of cotton aphids Aphis gossypii Glover over 5 consecutive days was significantly higher for S0, followed by R0 and R0.25, up to day 3 of observation. However, after day 4, prey consumption was similar among the three populations. 4 The results obtained in the present study show that resistant females have a lower reproductive output than susceptible females and that this is not related to the knockdown effect; however, the costs of recovering from knockdown interfere with the survival of offspring and also slightly with prey consumption. Thus, we conclude that the lambda‐cyhalothrin‐resistant E. connexa population exhibits an egg production disadvantage relative to the susceptible population and that this is increased when the population is subjected to prey scarcity.

Dietary effects upon biological performance and lambda-cyhalothrin susceptibility in the multicolored Asian lady beetle, Harmonia axyridis

Considered a generalist species among the coccinellids, the multicolored Asian lady beetle Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) feeds upon small arthropods and non-prey plant products, a practice which might enhance its ability to colonize various ecosystems but carries the potential to expose it to prey quality variation and insecticide use. Thus, we examined the effect of four different diets on the development, reproduction, and response to the insecticide lambda-cyhalothrin in this species. Three groups of larvae received laboratory-reared diets: (i) eggs of Anagasta kuehniella (Zeller) (Ak); (ii) eggs of Sitotroga cerealella (Olivier) (Sc); and (iii) eggs of A. kuehniella + S. cerealella at the proportion 1:1; and one group received wild-caught cotton aphids, Aphis gossypii Glover (Ag). Notwithstanding the generalist feeding behavior of H. axyridis, development and reproduction results were superior with diets of Ag or Ak compared with the diet combining 1:1 Ak + Sc or the diet of Sc eggs only. Furthermore, the Sc diet did not result in satisfactory development and reproduction. Despite this significant variation in biological responses, insecticide susceptibility studies using adults that had been reared on these diets showed no statistically significant differences in susceptibility to the lambda-cyhalothrin.

Dual resistance to lambda-cyhalothrin and dicrotophos in Hippodamia convergens (Coleoptera: Coccinellidae).

Insecticide resistance is usually associated with pests, but may also evolve in natural enemies. In this study, adult beetles of three distinct North American populations of Hippodamia convergens Guérin-Méneville, and the progeny of reciprocal crosses between the resistant and most susceptible population, were treated topically with varying concentrations of lambda-cyhalothrin and dicrotophos. In addition, the LD50s of both insecticides were applied in combination to resistant individuals. The developmental and reproductive performance of each population was assessed in the absence of insecticide exposure to compare baseline fitness. California and Kansas populations were susceptible to both materials, whereas Georgia (GA) beetles exhibited a resistance ratio (RR50) of 158 to lambda-cyhalothrin and 530 to dicrotophos. Inheritance of lambda-cyhalothrin resistance was X-linked, whereas inheritance of dicrotophos resistance was autosomal. Mortality of resistant beetles treated with a mixture of LD50s of both materials was twice that of those treated with lambda-cyhalothrin alone, but not significantly different from those receiving dicrotophos alone. Life history parameters were largely similar among populations, except that Georgia beetles had higher egg fertility relative to susceptible populations. We conclude that the high levels of resistance to lambda-cyhalothrin and dicrotophos in Georgia beetles reflect heavy loads of these insecticides in local environments, most likely the large acreage under intensive cotton cultivation.