Egg-larval Period Research Articles

Toxicity of some insecticides used in maize crop on Trichogramma pretiosum (Hymenoptera, Trichogrammatidae) immature stages

Fall armyworm Spodoptera frugiperda (J.E. Smith, 1797) (Lepidoptera: Noctuidae) is an important pest of maize (Zea mays L.) crops in Brazil. The effects of beta-cypermethrin, chlorfenapyr, chlorpyrifos, spinosad, etofenprox, triflumuron, alpha-cypermethrin/teflubenzuron, and lambda-cyhalothrin/thiamethoxam on Trichogramma pretiosum Riley, 1879 (Hymenoptera: Trichogrammatidae) immature stages were evaluated. Eggs of Anagasta kuehniella (Zeller, 1879) (Lepidoptera: Pyralidae), containing immature stages of the parasitoid were dipped in water solution pesticides, to evaluate their effects on emergence and sex ratio of F1 parasitoids. For F2 parasitoids, emergence, parasitism capacity, and sex ratio were evaluated. Beta-cypermethrin, chlorfenapyr, chlorpyrifos, and spinosad affected the emergence success of F1 T. pretiosum. Insects exposed to etofenprox and alpha-cypermethrin/teflubenzuron during the egg-larval period and to lambda-cyhalothrin/thiamethoxam during the pupal stage also suffered reduction in the emergence. Beta-cypermethrin affected the sex ratio of F1 T. pretiosum from host eggs treated during the egg-larval period; spinosad affected it during the egg-larval period and the pupal stage, whereas chlorpyrifos did the same when applied during the pupal stage. Chlorpyrifos also affected the sex ratio of F2 parasitoids, but only when applied during the egg-larval period, whereas chlorfenapyr reduced this trait when applied during the pre-pupal phase. Chlorpyrifos and alpha-cypermethrin/teflubenzuron affected the parasitism capacity of F1 females from eggs treated during the egg-larval period. Considering the overall effects, only etofenprox and triflumuron were selective on T. pretiosum when applied on parasitized A. kuehniella eggs. Further studies need to be carried out to verify the toxicity of the other pesticides under semi-field and field conditions.

Effects of insecticides used in corn on immature stages of Trichogramma atopovirilia (Hymenoptera: Trichogrammatidae)

The chemical control of Spodoptera frugiperda (Lepidoptera: Noctuidae) is difficult because caterpillars live inside the corn (Zea mays) cob and they do not come into contact with insecticides. Research on the use of parasitoids of the genus Trichogramma (Hymenoptera: Trichogrammatidae) has contributed to advances in alternatives for the control of this pest. However, there is little information on the effects of pesticides used in corn on these parasitoids. Therefore, the objective of this study was to evaluate the physiological selectivity of insecticides for Trichogramma atopovirilia in the egg-larval, pre-pupal and pupal phases. The bioassays were carried out under controlled conditions, exposing eggs of Anagasta (= Ephestia) kuehniella (Lepidoptera: Pyralidae) to parasitism for a 24-h period. The insecticides were sprayed using a Potter tower on host eggs containing the parasitoids in the egg-larval period, pre-pupal and pupal phases. The insecticides evaluated in g a. i. L-1 were: imidacloprid/ß-cyfluthrin (Connect 100TM SC - 0.033), chlorfenapyr (Pirate 240TM SC - 0.6), chlorpyriphos (Astro 450TM EW - 0.75), novaluron (Rimon 100TM CE - 0.05), spinosad (Tracer 480TM SC - 0.16) and triflumuron (Certero 480TM SC - 0.048). Water was used as a control. According to the results, the products were classified in the following toxicological classes for T. atopovirilia: imidacloprid/ßcyfluthrin, novaluron and triflumuron as harmless (class 1); spinosad and chlorfenapyr as slightly harmful (class 2); and Chlorpyrifos was harmful (class 4) to the parasitoid. Therefore, new studies under greenhouse and field conditions are necessary to confirm these toxicity results.

Effects of the mixed biocide Bacillus thuringiensis-abamectin on the development of the parasitoid Microplitis mediator and its host Helicoverpa armigera

The effects of the mixed biocide Bacillus thuringiensis Berliner with abamectin (BtA) on the development of the parasitoid Microplitis mediator (Haliday) (Hymenoptera: Braconidae) and its cotton bollworm host, Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae), were evaluated in the laboratory. Weight gain in larvae of H. armigera was initially delayed, but larval developmental period increased and pupal weight increased when they were fed on a diet containing BtA. Due to increased longevity of the host larvae, the susceptible period to parasitization of H. armigera by M. mediator increased when the host larvae were reared on diets containing BtA at concentrations of 0.5, 1, 2, and 4 μg g -1 . The longevity of female and male parasitoids significantly decreased when newly emerged wasps were fed a honey solution containing 200 μg ml -1 BtA in comparison with those fed only a honey solution. Mean longevity was significantly prolonged when parasitoids were fed a honey solution and BtA-honey solution in comparison with those fed BtA-distilled water, distilled water, or nothing. There were no significant differences compared with the control in any biological characteristics for the offspring of female parasitoids fed the honey solutions containing BtA at concentrations of 50, 100, and 200 μg ml -1 ; characteristics measured include the egg-larval period, pupal weight, male and female pupal periods, adult fresh weight, and adult longevity. When female parasitoids parasitized host larvae that had been fed the diet containing BtA, their male and female pupal periods were significantly prolonged compared with the control (without BtA).

Effect of chemical insecticides used in tomato crops on immature Trichogramma pretiosum (Hymenoptera: Trichogrammatidae)

The effects of the chemical insecticides acetamiprid, lufenuron, imidacloprid, novaluron, triflumuron, and pyriproxifen on the developmental stages of Trichogramma pretiosum were evaluated. Eggs of Anagasta kuehniella glued on blue paper cards were offered to T. pretiosum females for 24 h. after parasitization, the eggs were treated by dipping the cards into the insecticide solutions or in water for 5 s after they had reached the egg-larval, pre-pupal, or pupal stages. The application of pyriproxifen to T. pretiosum during its egg-larval period was slightly harmful to the parasitization capacity of F1 generation females and the emergence rate of F1 and F2 generation adults. When applied to T. pretiosum in the egg-larval period, acetamiprid was slightly harmful to the parasitization capacity of the F1 generation females of T. pretiosum. When applied to T. pretiosum in the pupal stage, acetamiprid was slightly harmful to the parasitization capacity of F2 generation females. When applied during the egg-larval period, imidacloprid was slightly harmful to the parasitization capacity of T. pretiosum females of the F1 generation. Lufenuron applied on T. pretiosum in the pupal stage was slightly harmful to the parasitization capacity of the F2 generation females. The insecticides novaluron and triflumuron, when applied during the immature stages to T. pretiosum, were harmless to its F1 and F2 generations.

The life parameters of a parasitoid Microplitis mediator (Hymenoptera: Braconidae), reared on cotton bollworm Helicoverpa armigera (Hübner) with Cry1Ac diet

Microplitis mediator (Haliday) is an important endoparasitoid of the cotton bollworm, Helicoverpa armigera (Hübner) in northern China. Interactions among H. armigera, its larval parasitoid M. mediator, and Cry1Ac over two generations were evaluated under laboratory conditions. The results indicated that the developmental period of M. mediator offspring's eggs and larvae were significantly delayed and pupal and adult weight were significantly less compared to the control when the female parasitoids parasitized H. armigera larvae that fed on diet containing 1, 2, 4 and 8 µg/g Cry1Ac. The female parasitoids emerged from the host fed diet containing 8 µg/g Cry1Ac could oviposit in healthy hosts, and their offspring's biological parameters (egg–larval period, pupal weight and adult weight), parasitism rate, abnormal cocoon rate and adult emergence were not significantly affected. Cry1Ac was detected in larvae and hemolymph of H. armigera, but not in the larvae of M. mediator. The results suggest that the observed significant effects on several fitness parameters of the F1 M. mediator developed from H. armigera fed Cry1Ac diet most likely were host-quality mediated rather than direct effects of Cry1Ac.

Effect of common wild crucifer species of Kenya on fitness of two exotic diamondback moth parasitoids, Cotesia plutellae and Diadegma semiclausum

Plutella xylostella is the most abundant and damaging pest of cruciferous crops in Kenya and has gained economic importance over the years. During a survey conducted in the major crucifer areas of Kenya a number of wild crucifers recorded in the region were found infested with diamondback moth. As a result, research was conducted in the laboratory and greenhouse to investigate whether exotic parasitoids recently introduced would develop and survive on the wild crucifers. Experiments were conducted on development, survival, reproductive potential and parasitism of Cotesia plutellae and Diadegma semiclausum on cultivated Brassica ( Brassica oleracea var. capitata and B. oleracea var. acephala) and wild crucifers ( Erucastrum arabicum, Raphanus raphanistrum, Rorippa micrantha, Rorippa nudiuscula and Brassica juncea). Both diamondback moth and parasitoids survived and developed on the wild crucifers. Egg-larval period of C. plutellae was shortest on E. arabicum (7.4 days) and longest on R. raphanistrum (9.3 days) while that of D. semiclausum was shortest on B. juncea (6.7 days). Ro. micrantha and R. raphanistrum recorded the lowest cocoon weight of 1.67 mg and 7.1 mg from C. plutellae and D. semiclausum, respectively. Longest pupal period was recorded on C. plutellae and D. semiclausum reared on B. oleracea var. acephala and Ro. micrantha, respectively. Egg-adult development time of C. plutellae was significantly longer on R. raphanistrum (15.2 days) and shortest on B. juncea and E. arabicum (12.2 days) while that of D. semiclausum was longest on Ro. micrantha (16.1 days) and shortest on E. arabicum (12.4 days). Mortality was higher on wild crucifers than on the cultivated Brassica species. In free choice tests, parasitism and parasitoid emergence were significantly higher on cultivated cultivars. Relatively higher percentage of larvae exposed to C. plutellae was not re-collected. The results suggest that wild crucifers can support development of the exotic parasitoids and thus provide refugia, thereby lowering the risk of local parasitoid extinction after pesticide application or harvesting. However, they might also be a source for diamondback moth and their presence near cultivated crucifer fields could lead to early population build-up.

Larval summer diapause of Chrysocharis pubicornis (Zetterstedt) (Hymenoptera: Eulophidae), a pupal parasitoid of agromyzid leafminers: Sensitive stage for diapause induction and effects of cool exposure on diapause termination

We examined the sensitive stage to summer diapause induction of Chrysocharis pubicornis. Individuals of different ages were transferred from diapause-preventing (15°C–12L : 12D) to diapause-inducing conditions (25°C–16L : 8D) throughout the 22-day egg-larval period. Transferring 15-day-old (third instar larvae about to complete feeding) or younger individuals resulted in more than 60% diapause; however, less than 25% of larvae entered diapause when transferred at 18 days (full-grown, resting third instar) or older. This suggests that sensitivity is high in younger instars, but decreases in the last instar. Moreover, individuals transferred at 18 days emerged 15 days earlier than control individuals continuously reared at 15°C–12L : 12D. We also examined the effects of cooling treatment duration on diapause termination by exposing diapausing larvae to 15°C–12L : 12D for increasing periods, followed by transfer to 25°C–16L : 8D. The percentage of diapause termination and the time to adult emergence increased with the cooling period, and it took between 12 and 16 days for 50% of individuals to complete diapause. The diapause termination rate after 20-day cooling was similar to that under continuous cooling (<90%), but the time to emergence was significantly shortened by 15 days. The implications of our findings in an eventual biocontrol program are discussed.

Feminization of Japanese medaka ( Oryzias latipes) exposed to 17β-estradiol: Effect of exposure period on spawning performance in sex-transformed females

Two groups of Japanese medaka ( Oryzias latipes) were exposed to 17β-estradiol (E2: 150 ng/L, nominal concentration) for either a short-term exposure (STE: 0–31 days after fertilization (daf); egg-larval period) or a long-term exposure period (LTE: 0–81 daf; egg-adult period) and their subsequent spawning performance was compared in terms of fecundity, spawning time, and fertility. Most genetic males were transformed to phenotypic females by E2 following both short-term and long-term exposure, but spawning performance and gonad somatic index (GSI) of sex-transformed females (XY females) following long-term exposure were lower than those of sex-transformed females following short-term exposure and those of normal females (XX) in the control group. Sex-transformed females in the STE group and normal females possessed mature ovary, whereas most of the sex-transformed females in the LTE group possessed immature ovary, with most oocytes being in the pre-vitellogenic phase. Moreover, the chromosome types of first filial generation delivered from sex-transformed female in STE group composed with 51.9% as XY, 18.5% as YY, and 29.6% as XX. From these results, it seems that exposure to E2 until the end of the larval period produces sex-transformed medaka with high reproductive ability, similar to normal females, but longer exposure to E2 may inhibit sexual maturation in the sex-transformed female.

Development and survival of Apanteles flavipes (Cam.) (Hymenoptera, Braconidae) on Chilo partellus (Swinh.) (Lepidoptera, Pyralidae) larvae reared on gram-flour diet

The suitability of Chilo partellus (Swinh.) larvae reared on gram (Cicer arietinum) flour diet, for rearing of the parasite, Apanteles flavipes (Cam.), was determined. The successful parasitism on diet fed or control larvae (reared on maize stems) was almost equal. There was also no significant difference in the mean egg-larval period of the parasite developed on both kinds of the hosts. However, on diet reared larvae, significantly more parasite grubs (20.3/host) failed to pupate as compared with control larvae (3.5/host). Consequently, the parasite cocoon production/host on them declined significantly but not drastically as they supported more number of parasite grubs/host as compared to control larvae. Reasons of the failure of parasite grubs to pupate in diet are not certain but considering all the biological attributes of the parasite developed on diet reared larvae, the diet is recommended for its mass multiplication.