Heavy metals have been found to be endocrine disruptors in invertebrates.  Lead is one of the most widespread elements of contamination, but there has been no research about the effects of lead stress on vitellogenin (Vg) gene expression in insects exposed to lead over multiple generations.  In this paper, the effects of different concentrations of lead (0, 0.3, 4.8 and 76.8 mg kg^–1) on the expression of Vg in the beet armyworm over five successive generations were studied.  The results showed that lead stress had significant effects on Vg expression in a dose-dependent manner.  For females at the larval and adult stages, as lead concentration increased, Vg expression was significantly inhibited; for males at these two developmental stages, Vg expression was induced and increased as lead concentration increased.  In addition, with the increase over stressed generations, inhibited effects for females and induced effects for males at the larval and adult stages became increasingly more obvious.  However, at the pupal stage, Vg expression in the two genders was different from that at the larval and adult stages.  The results indicate that lead stress can upregulate Vg expression in males which should be a useful indicator for environmental risk assessment.

Sitobion avenae (F.) and Rhopalosiphum padi (L.) are two important pests of wheat in China.  They typically coexist in fields during the late period of wheat growth.  Sulfoxaflor is a novel sulfoximine insecticide that demonstrates broad-spectrum efficacy, especially in targeting sap-feeding insects.  This study was carried out to investigate the sublethal effects of sulfoxaflor on the development, longevity, and reproduction of two species of wheat aphids.  Our results showed that sublethal concentrations of sulfoxaflor did not cause significant effects on the fecundity or the longevity of the parent generation (F₀ generation) of either S. avenae or R. padi.  However, it caused transgenerational sublethal effects.  For S. avenae, adult longevity of F₁ generation was significantly decreased.  No significant differences were observed on the population parameters of S. avenae in the F₁ generation.  For R. padi, the adult preoviposition period (APOP) and the total preoviposition period (TPOP) of F₁ generation were significantly reduced.  The mean generation time (T) was significantly reduced in the R. padi F₁ generation.  What’s more, the intrinsic rate of increase (r_m) and the finite rate of increase (λ) were significantly increased in the R. padi F₁ generation.  Taken together, these results suggest that exposure to the LC₂₅ of sulfoxafl had no effects on the parent generation of S. avenae or R. padi, but it reduced adult longevity of S. avenae as a negative effect and increased the r_m and λ of R. padi in the first progeny generation, which may have an impact on the population dynamics of R. padi.

 

Cyantraniliprole is a novel anthranilic diamide insecticide with significant efficacy against Bemisia tabaci, an important pest insect worldwide.  In this study, we conducted reversion and selection work and genetic analysis, and determined cross-resistance spectrum and synergism of cyantraniliprole resistance based on the reported population, SX population, of B. tabaci collected from Shanxi Province, China.  Compared with a susceptible strain (MED-S), SX population, the field-evolved cyantraniliprole-resistant population exhibited 26.4-fold higher resistance to cyantraniliprole.  In SX, a sharp decline of cyantraniliprole resistance was shown in the absence of selection.  Another tested strain, SX-R, was established from SX population after successive selection with cyantraniliprole and recently developed 138.4-fold high resistance to cyantraniliprole.  SX-R had no cross-resistance to abamectin, imidacloprid, thiamethoxam, sulfoxaflor, or bifenthrin.  Genetic analysis illustrated that cyantraniliprole resistance in SX-R was autosomally inherited and incompletely dominant.  Additionally, piperonyl butoxide (PBO) significantly inhibited cyantraniliprole resistance in the SX-R strain.  In conclusion, the selection of SX with cyantraniliprole led to high resistance to cyantraniliprole which is incompletely dominant and no cross-resistance to several common types of insecticides.  Enhanced oxidative metabolism is possibly involved in the resistance of SX-R, yet target-site resistance could not be excluded. 

The migratory locust Locusta migratoria (Orthoptera, Acrididae) is one of the most important pests due to its extensive and severe damage to crops in large parts of Africa and Asia.  Biodegradable and ecologically natural products such as botanical insecticides are emerging candidates for replacement of usually applied chemical pesticides.  The crude methanolic extract of Pergularia tomentosa (PME) was investigated for their toxicity and physiological aspects on L. migratoria nymphs.  Results showed that treatment of newly emerged fourth and fifth instar nymphs resulted in significant mortality and significant repellent activity with an LC₅₀ value of 0.18 and 0.38%, respectively, after seven days of treatment.  The PME toxicity was also demonstrated by histopathological changes in the alimentary canal resulting in considerable disorganization and severe damage of the caeca and proventriculus structure.  The extract induced cellular immune reactions which manifested by a significant decrease in the number of the differential haemocyte counts (prohemocytes and plasmatocytes) and important cell lysis.  Data of biochemical analyses showed that the PME reduced the activity of acetylcholinesterase and induced the glutathione S-transferases.  The neurotoxic effect was confirmed by the histological alterations in the brain structure, particularly in the neurosecretory cells showing typical signs of cell necrosis.

Midgut extracts play crucial roles in food digestion and detoxification.  We evaluated the effect of pH on the profiles of the midgut extracts in rice leaffolder, Cnaphalocrocis medinalis and the degradation of activated Bt-toxins by the midgut extracts under different pH conditions.  Total protease activity increased slightly with the increase with the simulated pH in the midgut extracts and the maximal protease activity was observed at pH 10.5, while an upward trend was observed as the pH of reaction buffer increased.  Activity of chymotrypsin-like enzymes increased with pH, both in the buffer and midgut extracts, while the activity of trypsin-like enzyme was unaffected.  Degradation of the activated Cry2A by the midgut extracts enhanced as the pH increased.  Cry2A was fully degraded into smaller segments at pH 9.0–10.5.  Activated Cry1C protein at pH 9.0–10.5 was partially degraded by the midgut extracts.  Activated Cry1Aa and Cry1Ac were partially degraded into fragments by the midgut extracts at high pH.  These results will facilitate our further understanding of the interactions between C. medinalis and the Cry toxin.

 

Three transgenic maize events (IE09S034, Shuangkang 12–5 and C0030.3.5) produced Cry1Ie, Cry1Ab/Cry2Aj and G10-EPSPS, Cry1Ab and EPSPS, respectively, all of which target the Asian corn borer.  The oriental armyworm Mythimna separata (Walker) is the secondary target.  In this study, the effects of the three Bt maizes on the development and survival of armyworm were studied.  The results showed that IE09S034 had insecticidal activity against 1st instar larvae, and the survival rate of armyworm fed with Bt maize for 10 days was 46.2%, significantly lower than that of the control.  The larvae at 3rd–6th instar were more tolerant of the Bt toxin than the early instar larvae.  However, Shuangkang 12-5 had good insecticidal activity against 1st–5th instar larvae.  The mortality was nearly 100% when the larvae were fed with Shuangkang 12-5 before 3rd instar, and the toxin had quick-acting efficacy.  This event significantly inhibited the development of armyworm; that is, the larval duration of the 3rd and 4th instar larvae fed with Shuangkang 12-5 was prolonged by 4.5 and 3.0 days, respectively.  The pupal weight and egg number were also significantly lower than those of the control.  For C0030.3.5, it could control 1st–5th instar larvae effectively.  The mortality rates were all over 50% if 1st–3rd larvae were fed with this event.  The pupal weight of 4th–6th instar larvae fed with Bt maize were only 53.9, 56.8 and 54.6%, respectively, compared to that of the control.  The number of eggs laid was significantly less than the control.  The results indicate that all three transgenic maize events exhibit the potential to provide effective control of early instar larvae of armyworm, which can be commercialized in future to control lepidoptera pests such as Asian corn borer and armyworm.

 

The rice planthoppers, Nilaparvata lugens and Sogatella furcifera, are important sap-sucking pests of rice in Asia.  The mesoionic insecticide triflumezopyrim was previously shown to be highly effective in controlling both N. lugens and S. furcifera.  In this study, electropenetrography (EPG) was used to evaluate the effect of three triflumezopyrim concentrations (LC₁₀, LC₅₀ and LC₉₀) on the feeding behavior of N. lugens and S. furcifera.  EPG signals of planthoppes indicated that there were six different waveforms NP, N1, N2, N3, N4, and N5, which corresponded to non-penetration, stylet penetration into epidermis, salivation, extracellular movement of stylet, sap ingestion in phloem, and water ingestion in xylem during feeding.  Compared to untreated controls, triflumezopyrim at LC₅₀ and LC₉₀ prolonged the duration of the non-penetration period by 105.3 to 333.7%.  The probing frequencies of N. lugens exposed to triflumezopyrim at LC₁₀ and LC₅₀ were significantly increased; however, the probing frequencies of S. furcifera showed a significant decrease when exposed to triflumezopyrim at all concentrations.  Triflumezopyrim exposure prolonged the duration of salivation and shortened the duration of extracellular movement.  The duration of phloem sap ingestion decreased from 37.2 to 77.7% in the LC₅₀ and LC₉₀ treatments, respectively.  Differences in feeding behavior in response to triflumezopyrim and pymetrozine were minimal.  In summary, the results show that the LC₅₀ and LC₉₀ concentrations of triflumezopyrim inhibit the feeding activities of N. lugens and S. furcifera mainly by prolonging the duration of non-penetration and by shortening the duration of phloem sap ingestion, which may foster more efficient use of triflumezopyrim in Asia.