Effects of some insecticides used in maize (Zea mays L.) on preimaginal stages of Trichogramma evanescens Westwood (Hymenoptera: Trichogrammatidae)

WOS: 000371196700010Trichogramma evanescens Westwood (Hymenoptera: Trichogrammatidae) is used for biological control of European corn borer Ostrinia nubilais Hubner (Lepidoptera: Crambidae), one of the key pest of maize (Zea mays L.) (Poales: Poaceae) in Turkey. Considering other pests, there is a need for integration of chemical control and T. evanescens releases. Therefore, effects of chemical insecticides on T. evanescens should be known. In this study, effects of insecticides chlorpyrifos ethyl, indoxacarb, chlorantraniliprole, deltamethrin, lambda-cyhalothrin and novaluron on the preimaginal developmental stages of T. evanescens were investigated using egg card dipping method in laboratory conditions. Blue egg cards containing approximately 125 parasitised Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) eggs were dipped into insecticide solutions prepared at the recommended dose for 5 second at each developmental stage of T. evanescens. Emergence ratio, parasitism capacity, emergence and sex ratio of offsprings were determined. Chlorpyrifos ethyl caused 100% death for all developmental stages and classified as harmful (4) according to the guidelines of IOBC. Deltamethrin and lambda-cyhalothrin was harmless (1) to emergence ratio, but caused reduction on the parasitism capacity (2) and the sex ratio of F-1. Novaluron was slightly harmful (2) when applied during the egg-larval period and harmless to F-1. Chlorantraniliprole and indoxacarb were harmless (1) for all developmental stages

Combined Non-Target Effects of Insecticide and High Temperature on the Parasitoid <i>Bracon nigricans</i>

<div><p>We studied the acute toxicity and the sublethal effects, on reproduction and host-killing activity, of four widely used insecticides on the generalist parasitoid <i>Bracon nigricans</i> (Hymenoptera: Braconidae), a natural enemy of the invasive tomato pest, <i>Tuta absoluta</i> (Lepidoptera: Gelechiidae). Laboratory bioassays were conducted applying maximum insecticide label rates at three constant temperatures, 25, 35 and 40°C, considered as regular, high and very high, respectively. Data on female survival and offspring production were used to calculate population growth indexes as a measure of population recovery after pesticide exposure. Spinetoram caused 80% mortality at 25°C and 100% at higher temperatures, while spinosad caused 100% mortality under all temperature regimes. Cyantraniliprole was slightly toxic to <i>B</i>. <i>nigricans</i> adults in terms of acute toxicity at the three temperatures, while it did not cause any sublethal effects in egg-laying and host-killing activities. The interaction between the two tested factors (insecticide and temperature) significantly influenced the number of eggs laid by the parasitoid, which was the lowest in the case of females exposed to chlorantraniliprole at 35°C. Furthermore, significantly lower <i>B</i>. <i>nigricans</i> demographic growth indexes were estimated for all the insecticides under all temperature conditions, with the exception of chlorantraniliprole at 25°C. Our findings highlight an interaction between high temperatures and insecticide exposure, which suggests a need for including natural stressors, such as temperature, in pesticide risk assessments procedures.</p></div

Reduction coefficient <i>E</i>_<i>x</i> [6], Doubling time (<i>DT</i>) and Intrinsic rate of increase (<i>r</i>_<i>m</i>) [35] estimated for <i>Bracon nigricans</i> adults exposed to the four tested insecticides at three constant temperatures and for the control parasitoid population.

<p>Reduction coefficient <i>E</i>_<i>x</i> [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0138411#pone.0138411.ref006" target="_blank">6</a>], Doubling time (<i>DT</i>) and Intrinsic rate of increase (<i>r</i>_<i>m</i>) [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0138411#pone.0138411.ref035" target="_blank">35</a>] estimated for <i>Bracon nigricans</i> adults exposed to the four tested insecticides at three constant temperatures and for the control parasitoid population.</p

Sublethal effects on biocontrol activity.

<p>Means (± SEM) of number of host larvae killed in three days by each tested <i>Bracon nigricans</i> female previously exposed for three days to residues at three constant temperatures. Columns bearing the same letter (upper case letters: within the same temperature regime; lower case letters: within the same tested insecticide) are not significantly different (<i>P</i>>0.05; ANOVA with LSD post hoc test for multiple comparisons).</p

Lethal effects.

<p>Mean percentages (± SEM) of survival of <i>Bracon nigricans</i> adults when exposed for three days to insecticide residues at three constant temperatures. Columns bearing the same letter (upper case letters: within the same temperature regime; lower case letters: within the same tested insecticide) are not significantly different (<i>P</i>>0.05; ANOVA with LSD post hoc test for multiple comparisons).</p

Sublethal effects on reproduction.

<p>Means (± SEM) of number of eggs laid in three days by each tested <i>Bracon nigricans</i> female previously exposed for three days to residues at three constant temperatures. Columns bearing the same letter (upper case letters: within the same temperature regime; lower case letters: within the same tested insecticide) are not significantly different (<i>P</i>>0.05; ANOVA with LSD post hoc test for multiple comparisons).</p

Tested insecticides.

<p>* The maximum label rate for tomato with a volume of 1000L ha^-1of insecticide solutions were applied.</p><p>Tested insecticides.</p

Statistics from the multifactorial ANOVA used to analyze (A) the percentages of parasitoids found dead after 3 days of exposure to insecticides (mortality), (B) the total numbers of eggs laid (reproduction) and (C) the numbers of host larvae killed (biocontrol) by each <i>Bracon nigricans</i> female during the three days following the insecticide exposure.

<p><i>P</i> values indicates in bold are those significant at <0.05 level.</p

European corn borer (Ostrinia nubilalis Hbn., Lepidoptera: Crambidae): comparing the performance of a new bisexual lure with that of synthetic sex pheromone in five countries

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