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Neotropical Entomology

versão impressa ISSN 1519-566X

Neotrop. entomol. vol.39 no.6 Londrina nov./dez. 2010

https://doi.org/10.1590/S1519-566X2010000600021 

BIOLOGICAL CONTROL

 

Selectivity of neem to Trichogramma pretiosum Riley and Trichogrammatoidea annulata De Santis (Hymenoptera: Trichogrammatidae)

 

 

Celso L HohmannI; Flávia A C SilvaII; Tanara G de NovaesI

IÁrea de Proteção de Plantas, Instituto Agronômico do Paraná, CP 481, 86001-970 Londrina, PR, Brasil; celuiz@iapar.br; tanaragn@hotmail.com
IICurso de Pós-Graduação em Ciências Biológicas, Univ Federal do Paraná, CP 19020, 81531-980 Curitiba, PR, Brasil; flacloclet@yahoo.com.br

 

 


ABSTRACT

Trichogramma pretiosum Riley and Trichogrammatoidea annulata De Santis are commonly found in avocado and persimmon orchards in northern Parana state. However, their abundance depends on whether insecticides are used or not to control the key lepidopteran pests Stenoma catenifer (Wals.) (Lepidoptera: Elachistidae) and Hypocala andremona (Stoll) (Lepidoptera: Noctuidae), respectively. The aim of this work was to evaluate the effects of an aqueous neem seed extract (ANSE) at 15, 3 and 1.5%, and of an emulsifiable concentrate neem oil (ECNO) at 2.5, 0.5 and 0.25% on lifetime parameters of these trichogrammatids as a way of testing the feasibility of integrating the biological and chemical control methods. Chemicals were applied on Anagasta kuehniella (Zeller) (Lepidoptera: Pyralidae) eggs before or after parasitization (one, three or five days). ANSE was more deleterious to both parasitoid species than ECNO, regardless of the concentration and the time of application. The chemicals acted on a concentration and time dependent manner. Treating the host with neem before parasitism was less deleterious to wasp emergence, especially for T. annulata. Pre-treatments (24h) of the host eggs with ECNO at concentrations varying from 0.5% to 0.25% did not affect T. pretiosum longevity, but 2.5% reduced T. annulata survival. Feeding wasps with honey mixed with 0.25% ECNO negatively affected T. annulata survival.

Key words: Botanical insecticide, Azadirachta indica, egg parasitoid


 

 

Egg parasitoids of the genus Trichogramma are the most studied and successful taxa used in innundative releases against many economically import pests in the world. According to Hassan (1988) & Li (1994) these parasitoids were used in more than 30 million ha worldwide to control lepidopteran pests in agriculture and forestry.

The interest in Trichogramma in Brazil began in the early 80's and an enormous amount of information in different areas of knowledge have been obtained thereafter. This knowledge led to the development of projects aiming to use trichogrammatids to control lepidopteran pests in several crops, including Stenoma catenifer (Wals.) (Lepidoptera: Elachistidae) on avocado (Parra & Zucchi 2004).

Indigenous Trichogramma pretiosum Riley and Trichogrammatoidea annulata De Santis have been found parasitizing eggs of S. catenifer on avocado (Hohmann & Meneguim 1993) and of Hypocala andremona (Stoll) (Lepidoptera: Noctuidae) on persimmon orchards (Hohmann & Lovato 2003), in the State of Parana, Brazil. These parasitoids were frequent and constant in the majority of the orchards evaluated in northern Parana, but their abundance depends on whether pesticides were used to control pests. Natural parasitism in pesticide-free avocado orchards can surpass 60% (Hohmann et al 2003).

The side effects of broad-spectrum insecticides on nontarget organisms and the risks posed to the environment stress the need for ecologically sound pest management methods. One alternative that has proved effective to control various arthropod pests is the botanical insecticide neem, Azadirachta indica (Schmutterer & Singh 1995). These alternative methods are particularly suitable for more stable agroecosystems, which are characteristic of many small farms in Brazil.

Studies of the possible side effects of plant extracts on natural enemies have increased in the last years showing promising results (Raguraman & Singh 1999, Gonçalves-Gervásio & Vendramin 2004, Silva & Martinez 2004). According to Hohmann (2003, not publ.) the effects of botanical insecticides were evaluated in more than a hundred species of natural enemies, mainly hymenopterans, coleopterans, heteropterans and predaceous mites. However, their effects on life history parameters of biocontrol agents may vary according to its origin, formulation, concentration and the natural enemy itself, among other factors. Therefore, it is important to consider each specific condition to determine the potential of botanical insecticides in IPM programs.

The aim of this study was to determine the effects of neem on life history parameters of T. pretiosum and T. annulata as a way of testing the feasibility of integrating the biological control agents with the botanical insecticide neem. The side effects of neem on the two trichogrammatids were assessed by using commercial emulsible oil and an aqueous seed extract. The results of this study may have important impact on future farmer's pest control strategies in organic managed avocados orchards.

 

Material and Methods

Experiments. Two different sources of neem at three different concentrations were tested to evaluate their side effects on T. pretiosum and T. annulata. The aqueous neem seed extract (ANSE) was tested at 1.5, 3.0 and 15.0%, and the commercial product Dalneem® (0.5%), an emulsible concentrate of neem oil (ECNO) was tested at 2.5, 0.5 (concentration recommended by the industry) and 0.25%. Two other treatments were used for comparisons: deltamethrin (25 EC, 0.0075%) and water (control).

Parasitoid origin and colony maintenance. Trichogramma pretiosum and T. annulata were collected from S. catenifer eggs on avocado in Arapongas, PR, Brazil, in 2001, and used to initiate laboratory colonies by using parasitoid rearing units (8.5 x 2.5-cm glass shell vial) and UV-treated eggs of Anagasta kuehniella (Zeller) (Lepidoptera: Pyralidae) as hosts. Parasitoid (~ F10) colonies were started at different days to provide eggs for the experiments. Honey was provided as a carbohydrate food source for adult parasitoids.

Aqueous neem seed extract (ANSE) preparation. Neem seeds were collected from Azadirachta indica trees cultivated at IAPAR's Experimental Station in Paranavaí, PR. In order to prepare the stock concentration (T1 = 15%), 30 g of neem seeds were soaked in 200 ml of distilled water during 24h, grinded in a blender and filtered. The stock concentration was further diluted in distilled water to obtain the remaining concentrations for testing (T2 = 3.0%; T3 = 1.5%).

Side effects of host egg pre-treatment with neem formulations on T. pretiosum and T. annulata biological parameters. The ANSE (15%; 3% and 1.5%) and the ECNO (2.5%; 0.5% and 0.25%) formulations were applied on cards containing approximately 100 UV-treated A. kuehniella eggs, using a manual sprayer device. One, three or five days later the egg cards were individually placed into the rearing units and exposed to three parasitoid females (< 6h old) for 24h. At the fifth day after exposing the wasps to the treated host egg cards, the number of parasitized eggs and adult emergence were recorded.

This experiment followed a completely randomized factorial design 2 x 5 x 3 (species x treatment x days before host eggs were treated) and was replicated five times.

Side effects of host egg post-treatment with neem formulations on T. pretiosum and T. annulata biological parameters. Fifteen cards containing approximately 500 UV-treated A. kuehniella eggs/treatment were offered to hundreds of T. pretiosum or T. annulata (< 6h old) females for 24h inside 1 L jars. Egg cards were then removed and one, three or five days later (egg-larva, pre-pupa and pupa stages of the parasitoid, respectively) (Cônsoli et al 1999) were sprayed either with ANSE or ECNO at the previously mentioned concentrations, and placed into the rearing units for further evaluation. Parasitoid emergence was determined indirectly considering the number of host eggs containing exit holes.

This experiment followed a completely randomized factorial design 5 x 3 (treatments x days after host eggs were treated).

Side effects of neem on T. pretiosum and T. annulata longevity. The side effect of neem oil on T. pretiosum and T. annulata longevity was evaluated in two experiments that followed a completely randomized block design. In the first experiment three concentrations of ECNO (2.5, 0.50 and 0.25%) and water (control) were sprayed 24h before the host eggs were parasitized. In a second test, newly emerged females were fed 0.25% ECNO either mixed with pure honey or water. In both cases, isolated females (15 per experiment; one female = one replicate) were exposed to 200 eggs of A. kuehniella eggs for 24h. All tests and rearing were conducted at controlled conditions (25 ± 2ºC, 70 ± 20% RH, and 14L:10D photoperiod).

Statistical analysis. Treatment effects on host parasitization, longevity and adult emergence were subjected to ANOVA and means were compared using the Least Significant Difference t-test (Ferreira 2000). Data on the parasitization capacity and adult emergence were sqrt (x + 0.5) and arcsine transformed before analysis, respectively.

 

Results and Discussion

Side effects of host egg pre-treatment with neem formulations on T. pretiosum and T. annulata biological parameters. The analysis of the isolated effect of ANSE on parasitism capacity of T. pretiosum and T. annulata revealed significant differences for species and treatments, but not for spraying time. However, there were significant interaction between the last factor and treatments (Table 1). Spraying A. kuehniella eggs with 15% ANSE or 0.0075% deltamethrin one, three or five days before their exposure to T. pretiosum females (pre-treatment) reduced parasitization significantly (74% to 84%, 86% to 95% and 77% to 93%), respectively as compared with control treatment (Table 1). A drastic negative effect on the number of A. kuehniella eggs parasitized by T. pretiosum was also reported by Gonçalves-Gervásio & Vendramin (2004) after application of 10% aqueous neem seed extract. The parasitism rates of wasps exposed to lower doses (3% and 1.5%) were not negatively affected.

The effect of the neem seed extract on parasitism capacity of T. annulata females was more severe as compared to T. pretiosum, especially when the host eggs were sprayed 24h before the wasps had access to them. Under this condition all treatments differed from control and mortality reached up to 100% (Table 1). In the following period (three days) only the lower concentration (1.5%) was not harmful to T. annulata females and at five-day period only deltamethrin significantly reduced parasitism.

As occurred with ANSE data there were significant differences for species and for treatments, but not for insecticides application time when ECNO was tested. In addition significant interactions existed for insecticide and days and for the three factors (Table 2). Pre-treatment of A. kuehniella eggs with ECNO (2.5%) or deltamethrin (0.0075%) 24h after exposure to the wasps also reduced (over 85%) parasitism by T. pretiosum. The lower concentrations had no negative effect of parasitism rates (Table 2). The same trend was observed for the remaining time intervals. In contrast to the findings reported here, Rocha et al (unpubl.) mentioned reduction on parasitism when neem oil at 0.5 and 0.25% was tested on T. pretiosum on A. kuehniella eggs.

Similarly to ANSE, T. annulata females were more susceptible to ECNO than T. pretiosum. Reduction in parasitism capacity surpassed 95% when T. annulata females were pretreated (24h) with ECNO (2.5%) or deltamethrin (0.0075%) (Table 2). The lower concentrations of ECNO did not reduce parasitism significantly. The effect of the oil was even more drastic at the third day pre-tretment period, and at the fifth day after spraying, despite the drastic reduction on parasitism on most of the treatments, the differences were not significant.

Side effects of host egg post-treatment with neem formulations on T. pretiosum and T. annulata biological parameters. Post-treatment of the host eggs 24h after parasitism (egg-larval stage) with ANSE 15% or 3% reduced T. pretiosum emergence by 86% and 58%, respectively, in comparison with control treatment (Table 3). For the remaining developmental stages only the highest neem concentration significantly affected T. pretiosum emergence. This is an indicative that the egg-larval developmental period was the most susceptible stage when T. pretiosum was exposed to A. kuehniella eggs treated with ANSE (Table 3). Gonçalves-Gervásio & Vendramin (2004) reported also reduction on emergence of T. pretiosum on A. kuehniella eggs sprayed with 10% aqueous neem extract. However, the authors found the pupa as the most susceptible developmental stage. Differences due to parasitoid intrinsic characteristics and/or methodological differences may explain the contradictory results.

Anagasta kuehniella eggs treated with ECNO 2.5% or deltamethrin 0.0075% reduced T. pretiosum emergence in comparison with control treatment (Table 4). The same response was obtained with 2.5% and 0.5% concentrations for eggs treated three days after parasitization by T. pretiosum. Spraying the host eggs with neem oil at 2.5, 0.5 or 0.25%, three days (prepupal stage) after parasitization, resulted in much drastic effect on emergence than when the eggs were treated 24h (egg-larval stage) after parasitism (Table 4). However, there was no apparent differences between hosts treated 24h or five days after parasitism as well as on the effects of the compounds on the emergence for the later time (five days) period. The results indicated that 3-day-old (pre-pupal stage) parasitized eggs were more susceptible to neem oil. Contrasting results were reported by Raguraman & Singh (1999), who did not found influence of the neem seed oil extract (0.3 to 5%) on immature development and adult emergence of T. chilonis females exposed to post-treated C. cephalonica eggs. Similarly, Oliveira et al (2003) revealed no significant effect on emergence of T. pretiosum reared on A. kuehniella eggs when the commercial neem oil (1.25 to 2.0%) was used.

Effect of neem on T. pretiosum and T. annulata survival. Treating host eggs with ECNO at concentrations varying from 2.5% to 0.25%, 24h before exposing them to females, did not affect T. pretiosum longevity, but the highest concentration (2.5%) reduced T. annulata survival (Table 5). Oliveira et al (2003), however, reported significant reduction on longevity of T. pretiosum on A. kuehniella eggs even when concentrations varying from 1.25% to 2% were tested.

 

 

Feeding T. pretiosum with honey mixed with ECNO 0.25% did not affect female's longevity when compared to those feeding on concentrated honey alone (Fig 1). In contrast, this mixture reduced longevity of T. annulata in 70%. Raguraman & Singh (1999) tested the effect of neem seed oil (0.3 to 5.0%) mixed with honey on T. chilonis longevity and did not find influence of the botanical insecticide on survival of males and females. The different response of the parasitoid species to the ingestion of honey mixed with neem oil may be due to intolerance to the botanical insecticide.

 

 

The effect of neem on biological parameters of parasitoids varied according to the species, product formulation, concentrations and time of application. Trichogramma pretiosum was less affected by the botanical insecticide than its counterpart. Comparisons on the effects of the two neem formulations (ANSE or ECNO) on parasitism capacity revealed that the aqueous neem extract was more deleterious than the emulsible neem oil, however, the differences were significant only for T. pretiosum (P < 0.0005). The same response was observed when the effect of both formulations on the emergence of T. pretiosum was compared (P < 0.0000).

The reasons for more severe side effects of ANSE to the parasitoids were not clear, but could be related to the higher toxicity of the aqueous neem seed extract doses used as compared to the doses of the commercial oil, or due to higher concentration of azadirachtin in the aqueous solution. These hypotheses, however, need to be proved correct.

The time of spraying (pre or post-treatment) had different consequences to parasitoid survival. Treating the host eggs before exposing them to the females was more detrimental to parasitoid development and emergence than when the compounds were otherwise sprayed. Treating hosts after parasitization avoids the deterrent effects and mortality that the products may cause on adult wasps, thus affecting parasitism rates. Moreover, post-treatment of the host eggs affects less wasp emergence; this is more evident for T. annulata, either treated with ANSE or ECNO (Hohmann unpubl.). When spraying occurs after parasitism the immatures will be well protected inside the host eggs shell as it is well documented here and elsewhere (Raguraman & Singh 1999, Gonçalves-Gervásio & Vendramin 2004), except when the compounds were used at the highest concentrations.

The sensitivity of the parasitoid immatures, nonetheless, varies with its developmental stage and with neem formulation. The egg-first larval instar was the most affected stage when ANSE was used, whereas ECNO was more deleterious to prepupal stage.

Despite the data showed differences between the two egg parasitoid species, favoring T. pretiosum, additional studies are needed, using natural hosts under field conditions, to have a more reliable response of the side effects of the botanical insecticide on theses beneficial insects. The outcome of this study may contribute to a better understanding of the potentialities of using an integrated control approach, including egg parasitoids of the family Trichogrammatidae and neem, to control avocado and persimmon lepidopterous pests in organic managed systems.

 

Acknowledgments

The authors are thankful to Adauto Crispim for technical support and Dr Sueli S Martinez for the critical review of an earlier version of the manuscript. Also to Ines Fumiko Ubukata Yada for valious help with the statistical analyses.

 

References

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Schmutterer H, Singh R P (1995) List of insect pests susceptible to neem products, p.326-365. In Schmutterer H (ed) The neem tree Azadirachta indica A. Juss. and other meliaceous plants - Source of unique products for pest management and other purposes. Weinheim, VCH, 696p.         [ Links ]

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Received 16/III/09.
Accepted 05/I/10.

 

 

Edited by José R P Parra - ESALQ/USP

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