Genetic transformation of 'Hamlin' and 'Valencia' sweet orange plants expressing the cry11A gene of Bacillus thuringiensis as an additional tool for the management of Diaphorina citri (Hemiptera: Liviidae).

The Asian citrus psyllid (ACP) Diaphorina citri Kuwayama (Hemiptera: Liviidae) is the vector of Candidatus Liberibacter spp., the bacteria associated with huanglongbing (HLB), the most devastating disease of citrus worldwide. HLB management has heavily relied on insecticide applications to control the ACP, although there are efforts towards more sustainable alternatives. In previous work, our group assessed the potential bioactivity of different strains of Bacillus thuringiensis (Eubacteriales: Bacillaceae) (Bt) containing cry/cyt genes as feasible tools to control ACP nymphs. Here, we report an attempt to use the cry11A gene from Bt to produce transgenic sweet orange plants using two promoters. For the genetic transformation, 'Hamlin' and 'Valencia' sweet orange seedlings were used as sources of explants. Transgenic plants were detected by polymerase chain reaction (PCR) with specific primers, and the transgene copy number was confirmed by Southern blot analyses. Transcript expression levels were determined by qPCR. Mortality assays of D. citri nymphs were carried out in a greenhouse, and the effect of the events tested ranged from 22% to 43% at the end of the five-day exposure period. To our knowledge, this is the first manuscript reporting the production of citrus plants expressing the Bt cry11A gene for the management of D. citri nymphs.

Impacts of seven insecticides on Cotesia flavipes (Cameron) (Hymenoptera: Braconidae).

The endoparasitoid wasp Cotesia flavipes (Cameron) (Hymenoptera: Braconidae) is inundatively released in Brazilian sugarcane plantations to control the sugarcane borers Diatraea saccharalis (Fabricius) and Diatraea flavipennella (Box) (Lepidoptera: Crambidae). In conjunction with these releases, several synthetic insecticides are used to control the neonate larvae of these pests. We assessed the lethal and transgenerational sublethal effects of seven of these insecticides on C. flavipes. Leaf discs were sprayed at the highest field concentrations of chlorantraniliprole, lambda-cyhalothrin + chlorantraniliprole, chlorfluazuron, triflumuron, lambda-cyhalothrin + thiamethoxam, tebufenozide, and novaluron. Distilled water was used as a negative control. Newly emerged females (24 h old) were placed in Petri dishes containing the treated leaves, and the lethal and transgenerational sublethal effects were assessed for the next two generations. Lambda-cyhalothrin + chlorantraniliprole and lambda-cyhalothrin + thiamethoxam caused 100% mortality of the parasitoid and were highly persistent, causing more than 30% mortality at 30 days after spraying. Chlorantraniliprole, chlorfluazuron, novaluron, and triflumuron did not cause significant mortality compared to the negative control, but did have transgenerational sublethal effects. The length of the tibia of the right posterior leg, used as a growth measurement, was reduced in the progeny (F1 generation) of exposed female parasitoids. In addition, chlorantraniliprole increased and chlorfluazuron reduced the proportion of females in the F1 generation, whereas novaluron reduced the proportion of females in the F2 generation. Overall, only tebufenozide was considered harmless to C. flavipes. The results of this study suggest that lambda-cyhalothrin + chlorantraniliprole and lambda-cyhalothrin + thiamethoxam are harmful to C. flavipes, although field studies are needed to obtain results for actual sugarcane crops.

The impact of six insecticides commonly used in control of agricultural pests on the generalist predator Hippodamia convergens (Coleoptera: Coccinellidae).

Hippodamia convergens is an important predator found in different agroecosystems. We evaluated the impacts of six insecticides on eggs, larvae and adults of this predator. For eggs, all insecticides reduced larval hatching rates, but did not affect egg duration. Chlorpyrifos and phosmet reduced larval survival; and chlorpyrifos, etofenprox and phosmet prolonged the larva development time. The survival and duration of pupae were not affected by all insecticides tested. Chlorpyrifos reduced fecundity, fertility and longevity when eggs were sprayed. For first-instar larvae, chlorpyrifos, etofenprox, phosmet and imidacloprid caused 100% mortality, while azadirachtin and thiamethoxam caused 35.0 and 52.7% mortality, respectively. However, azadirachtin and thiamethoxam did not affect the other biological parameters of the predator. In adults, chlorpyrifos, etofenprox and phosmet reduced adult survival. Chlorpyrifos, etofenprox, and phosmet reduced fecundity and longevity, but did not affect fertility. Azadirachtin, imidacloprid and thiamethoxam did not affect fecundity, fertility or longevity. Based on demographic parameters, all insecticides reduced the net reproductive rate (Ro), intrinsic rate of increase (r) and finite rate of increase (λ) of the predator when eggs were treated directly. Azadirachtin, chlorpyrifos, etofenprox and phosmet increased the mean generation time (T), while the effects of imidacloprid and thiamethoxam were similar to the control. When first-instar larvae were treated, azadirachtin and thiamethoxam reduced the Ro, r and λ. Thiamethoxam increased the T value, while the effects of the other insecticides were similar to the control. These insecticides should be used with caution, in order to reduce their harmful effects on the predator in agroecosystems.

Sublethal effects of pyrethroid and neonicotinoid insecticides on Iphiseiodes zuluagai Denmark and Muma (Mesostigmata: Phytoseiidae).

The predator mite Iphiseiodes zuluagai Denmark & Muma is an important biological-control agent of mite pests, and it is one of the most common species found in citrus orchards. This study assessed, under laboratory conditions, the toxicity and duration of the harmful effects of five insecticides, the three pyrethroids deltamethrin, esfenvalerate and lambda-cyhalothrin, and the two neonicotinoids imidacloprid and thiamethoxam on I. zuluagai. Furthermore, we estimated the life-table parameters of the predator. Our results showed that deltamethrin and lambda-cyhalothrin caused higher mortality of larvae and adults than imidacloprid and thiamethoxam. In contrast, esfenvalerate provided larval mortality similar to imidacloprid and thiamethoxam, but it did not cause significant adult mortality of the predator. Mites that developed on pyrethroid residues showed lower survival of the immature stages, fecundity, and longevity compared to neonicotinoid residues and the control treatment. The estimated life-table parameters indicated that deltamethrin, lambda-cyhalothrin and esfenvalerate caused greater reduction in R o and r of I. zuluagai compared with imidacloprid and thiamethoxam, which were similar to the control treatment. Besides the impacts on biological and population parameters, the duration of the harmful activity of pyrethroid insecticides was longer than the neonicotinoids. Therefore, the use of pyrethroid insecticides to control pest insects may involve serious implications for integrated pest-management programs that aim to exploit the biological control by I. zuluagai in citrus orchards.