Do fall armyworm’s Metaflumizone resistante populations affect the activity of Trichogramma pretiosum?

The possible interference of resistant pest’s populations to insecticides in natural enemies in the action thas not been clarified yet. Thus, this study aimed to evaluate Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) performance on Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) eggs with resistance frequency to the Metaflumizone over six generations of product exposure. Egg cards (2.0 x 7.0 cm) containing eggs from two populations of S. frugiperda, (resistant to Metaflumizone and the other susceptible), were exposed to T. pretiosum females for 24 hours in free-choice and no-choice testing in three generations (G1, G4, and G6). A completely randomized experimental design was used with 25 replications, each consisting of an egg card (experimental unit) containing 20 eggs. The parameters evaluated were: parasitism (%), emergence (%), sex ratio, number of emerged parasitoids per egg and males/females longevity. ANOVA and Tukey test (P≤ 0.05) were applied on the results. Results showed a reduction in parasitism [41.0% (G1) and 28.4% (G4)], egg emergence (17.5%) and parasitoids/egg [16.2 (G4) and 17.2 (G6)] in eggs originating from the population with resistance frequency. Females emerging from G6 populations eggs without exposure to Metaflumizone had greater longevity (3.5 days more) than the resistant population. The sex ratio and male longevity were not affected. The results indicate a reduction in T. pretiosum activity if S. frugiperda populations have some frequency of resistance to Metaflumizone.

INFLUÊNCIA DA IDADE DE OVOS DE TRICHOPLUSIA NI (LEPIDOPTERA: NOCTUIDAE) EM FÊMEAS DE TRICHOGRAMMA PRETIOSUM (HYMENOPTERA: TRICHOGRAMMATIDAE) EM DIFERENTES TEMPERATURAS

Objetivamos avaliar a influência da idade dos ovos de Trichoplusia ni (Lepidoptera: Noctuidae) em fêmeas de Trichogramma pretiosum (Hymenoptera: Trichogrammatidae), em diferentes temperaturas. Assim, ovos de T. ni com idade ≤ 12, ≤ 24, ≤ 36, ≤ 48, ≤ 60 e ≤ 72 horas de desenvolvimento embrionário, separados a temperaturas de 20, 25 e 30 ºC, foram oferecidos para fêmeas de T. pretiosum com até 24 horas de idade. O parasitismo foi inversamente proporcional ao desenvolvimento embrionário do ovo, com maiores taxas de parasitismo observadas para ovos com até 24 horas de desenvolvimento embrionário nas três temperaturas. A viabilidade do parasitismo foi influenciada pela idade dos ovos. Os ovos, com até 36 horas de idade, apresentaram viabilidade superior a 85% nas três temperaturas. A proporção sexual a 25ºC apresentou a melhor taxa dentro da faixa de desenvolvimento embrionário. O número de descendentes do parasitoide por ovo foi influenciado pela temperatura e pela idade dos ovos, sendo a combinação ovos com 60-72 horas à temperatura de 30ºC, a que apresentou o maior quantitativo de descendentes parasitoides por ovo. Esses resultados indicaram que a idade do hospedeiro e a temperatura ambiente podem alterar as características biológicas dos parasitoides.

Olfactory Sensilla and Olfactory Genes in the Parasitoid Wasp Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae)

Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) is a tiny natural egg parasitoid of several agricultural pest insects, which has been widely used in the biological control for Plutella xylostella, Helicoverpa armigera, Spodoptera frugiperda and Ectomyelois ceratoniae. However, limited studies have been conducted on T. pretiosum olfactory system, which is critical in regulating insect behaviours. In this study, T. pretiosum adult antennae were investigated under ascanning electron microscopy (SEM). Four types of olfactory sensilla were observed, including chaetica sensilla (CS), trichoid sensilla (TS), faleate sensilla (FS) and placoid sensilla (PS). Using T. pretiosum genome, 22 putative odorant binding proteins (OBPs) and 105 odorant receptors (ORs) were identified, which were further compared with olfactory genes of Apis mellifera, Nasonia vitripennis and Diachasma alloeum. The expression patterns of OBPs between T. pretiosum male and female adults were examined by quantitative real time PCR (qRT-PCR) approaches. Three female-specific OBPs (TpreOBP19, TpreOBP15 and TpreOBP3) were identified, which may play crucial roles in T. pretiosum host-seeking and oviposition behaviours. This study enriches our knowledge of T. pretiosum olfactory genes and improves our understanding of its olfactory system.

Lethal, Sublethal And Transgenerational Effects of Insecticides Labeled For Cotton On Immature Trichogramma Pretiosum

The egg parasitoid Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) regulates lepidopteran pest populations in cotton crops. However, cotton harbors dozens of pests, and growers rely on multiple insecticide applications to manage these damaging organisms. A harmonious integration of control tactics is required for proper pest management, and the use of selective insecticides (i.e., those promoting effective pest control while causing little impact on natural enemies) fits within this scope. This study aimed to assess the lethal, sublethal and transgenerational effects of insecticides from varying chemical groups on T. pretiosum. The insecticides were sprayed on parasitized host [Ephestia kuehniella (Zeller)] eggs with developing T. pretiosum stages (egg-larva, prepupa and pupa), and biological traits were assessed following adult emergence. Overall, pupae were more susceptible to the insecticides. We found thiodicarb and chlorfenapyr to reduce F0 adult emergence in rates comparable to the positive control (methomyl). Adult F0 deformation was the highest on flupyradifurone-treated organisms, and both the F0 parasitism rate and female survival were reduced by the insecticides (except for teflubenzuron). The sex ratio was affected by thiodicarb and flupyradifurone. Transgenerational effects occurred on adult emergence, which was reduced on the offspring (F1) of thiodicarb-, chlorfenapyr-, and flupyradifurone-treated T. pretiosum. In addition, thiodicarb lessened the F1 sex ratio. Combined, these results indicate that teflubenzuron is the safest insecticide; the other insecticides (especially thiodicarb and chlorfenapyr) are non-selective to T. pretiosum. Field and semifield studies are required to confirm the harmfulness of thiodicarb and chlorfenapyr towards T. pretiosum.

Parasitism of Trichogramma Pretiosum in Eggs of Corcyra Cephalonica on the Age of the Parasitoid and the Density of the Host

Several biological control programs use Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae). The parasitism capacity and the functional response of T. pretiosum parasitizing eggs of Corcyra cephalonica (Stainton) (Lepidoptera: Pyralidae) were studied. To determine the parasitism capacity, females of the parasitoid were individualized, being offered to each female eggs from the host. Daily observations determined the number of parasitized eggs per female, accumulated percentage of parasitism, female longevity and percentage of parasitoid emergence. To establish the functional response, T. pretiosum females were individualized and offered C. cephalonica eggs. Number of parasitized eggs and percentage of adults’ emergence were evaluated, being calculated handling time (Th) and attack rate (a). On the first day of the parasitoid’s life there was parasitism in more than 80% of the host eggs, similar to the percentage of adult emergence throughout the life cycle, and the daily percentage of parasitism. The percentages of eggs of C. cephalonica parasitized were statistically different, with the quadratic model better describing the parasitoid-host relationship, with a positive value of 0.00594, since with the increase in the availability of eggs of C. cephalonica, parasitism was increased. The attack rate was approximately 0.00158, while the handling time of the host eggs was 0.6884 h.

Olfactory response of Trichogramma pretiosum (Hymenoptera: Trichogrammatidae) to volatiles induced by transgenic maize

Plants not only respond to herbivorous damage but adjust their defense system after egg deposition by pest insects. Thereby, parasitoids use oviposition-induced plant volatiles to locate their hosts. We investigated the olfactory behavioral responses of Trichogramma pretiosum Riley, 1879 (Hymenoptera: Trichogrammatidae) to volatile blends emitted by maize (Zea mays L.) with singular and stacked events after oviposition by Spodoptera frugiperda Smith, 1797 (Hymenoptera: Trichogrammatidae) moths. Additionally, we examined possible variations in gene expression and on oviposition-induced volatiles. We used a Y-tube olfactometer to test for the wasp responses to volatiles released by maize plants oviposited by S. frugiperda and not-oviposited plants. Using the real-time PCR technique (qRT-PCR), we analyzed the expression of lipoxygenase and three terpene synthases genes, which are enzymes involved in the synthesis of volatile compounds that attract parasitoids of S. frugiperda. Olfactometer tests showed that T. pretiosum is strongly attracted by volatiles from transgenic maize emitted by S. frugiperda oviposition (VTPRO 3, more than 75% individuals were attracted). The relative expression of genes TPS10, LOX e STC was higher in transgenic hybrids than in the conventional (isogenic line) hybrids. The GC-MS analysis revealed that some volatile compounds are released exclusively by transgenic maize. This study provides evidence that transgenic hybrids enhanced chemical cues under oviposition-induction and helped to increase T. pretiosum efficiency in S. frugiperda control. This finding shows that among the evaluated hybrids, genetically modified hybrids can improve the biological control programs, since they potentialize the egg parasitoid foraging, integrating pest management.