Intercrop movement of convergent lady beetle, Hippodamia convergens (Coleoptera: Coccinellidae), between adjacent cotton and alfalfa

Olfactometer Responses of Convergent Lady Beetles Hippodamia convergens (Coleoptera: Coccinellidae) to Odor Cues from Aphid-Infested Cotton Plants Treated with Plant-Associated Fungi

Simple Summary

The cotton aphid Aphis gossypii is a serious agricultural pest. Microbes associated with plants can affect the behavior and performance of insect herbivores and their natural enemies. Phialemonium inflatum and Chaetomium globosum fungi can reduce cotton aphid reproduction when applied as a seed treatment to cotton. We evaluated whether these fungi might affect the interaction between cotton aphids and a natural enemy, the convergent lady beetle Hippodamia convergens. We used dual-choice olfactometer experiments to assess lady beetle behavioral responses to cues from fungal-treated cotton plants in the presence or absence of aphid infestations. In the absence of fungal treatments, males preferred odors from aphid-infested relative to non-infested plants, and females spent more time associated with olfactory stimuli from aphid-infested versus non-infested plants. When cues from fungal-treated plants infested with aphids were assessed, there were no differences in lady beetle responses. The only fungal treatment-related effects involved plants without aphids. In the absence of aphids, males responded slower to P. inflatum-treated plants compared to control, and females preferred P. inflatum-treated plants. Treating cotton with these potentially beneficial fungi had minor effects on lady beetle behavioral responses and would not be expected to disrupt this predator–prey–plant interaction as part of an integrated pest management strategy.

Abstract

Microbes have the potential to affect multitrophic plant–insect–predator interactions. We examined whether cotton plants treated with potentially beneficial fungi affect interactions between cotton aphids Aphis gossypii and predatory lady beetles Hippodamia convergens. We used Y-tube olfactometer assays to test lady beetle behavioral responses to stimuli emitted by aphid-infested and non-infested cotton plants grown from seeds treated with either Phialemonium inflatum (TAMU490) or Chaetomium globosum (TAMU520) versus untreated control plants. We tested a total of 960 lady beetles (480 males and 480 females) that had been deprived of food for approximately 24 h. In the absence of any fungal treatments, males preferred stimuli from aphid-infested plants, and females spent more time associated with stimuli from aphid-infested versus non-infested plants. When fungal treatments were added, we observed that lady beetles preferred non-aphid-infested P. inflatum plants, and males responded slower to plants treated with P. inflatum in the absence of aphids. We found some evidence to suggest that lady beetle behavioral responses to plants might vary according to the fungal treatment but not strongly impact their use as part of an insect pest management strategy.

The Benefits of Omnivory for Reproduction and Life History of a Specialized Aphid Predator, Hippodamia convergens (Coleoptera: Coccinellidae)

The convergent lady beetle, Hippodamia convergens Guerin-Meneville, is a specialized predator of cereal aphids on the High Plains, completing its first generation each year in winter wheat, the resulting adults dispersing into summer crops and producing additional generations, contingent on the availability of aphids. In the present study, we tested the collective value of supplementary plant resources (sugars, pollen, and seedling wheat leaves), and small amounts of alternative prey, eggs of Ephestia kuehniella (Zeller) (Lepidoptera: Pyralidae), all provided together, for improving beetle life history and reproductive success even when suitable prey, Schizaphis graminum (Rondani) (Hemiptera: Aphididae), were provided ad libitum. Although a monotypic diet of S. graminum yielded slightly faster larval development and heavier adults than the omnivorous diet, preoviposition periods were extended and 21-d fecundities greatly reduced when this diet was continued through adult life, largely due to fewer oviposition days, although egg fertility was unaffected. The results highlight the critical importance of plant-derived resources even when suitable prey are not limiting. However, monotypic diet beetles that diapaused for 21 d in the presence of supplementary plant resources, plus moth eggs, achieved the same reproductive success as those reared on the omnivorous diet, with or without diapause, demonstrating that access to these resources post-emergence was sufficient to compensate for their absence during development. The diapause treatment itself had no impact on the fitness of beetles reared on the omnivorous diet, likely because neither its duration, nor the caloric restriction imposed, were sufficient to diminish reproductive effort.

Refinement of the Protein Immunomarking Technique for Mark-Capture Research

A follow-up study was conducted to further evaluate the marking efficiency of broadcast spray applications of egg albumin (from chicken egg whites) on Hippodamia convergens Guérin-Méneville (Coleoptera: Coccinellidae) in alfalfa. A previous study recorded exceptional marking efficiency (e.g., >95% of the population) on H. convergens when using relatively high concentrations (10 to 50%) of chicken egg whites. The present study examines marking efficiency of egg whites using lower concentrations of 2.5, 5.0, and 10.0%. We used cadaver and free-roaming beetles to measure protein mark acquisition (and retention) of each protein concentration by direct contact with the spray application and incidental contact with protein residue on the plant tissue, respectively. The vertical distribution of the protein mark was also determined by sampling the upper and lower portions of the alfalfa canopy. The data indicate, regardless of the egg white treatment, that the backpack sprayer provided uniform coverage of egg albumin on the alfalfa plants and cadaver beetles. Also, almost every free-roaming beetle acquired a mark within 24 h after contact exposure to protein marked plants. This study shows that a very low concentration of egg albumin is sufficient for marking arthropods directly in the field.

Effects of seed mixture sowing with transgenic Bt rice and its parental line on the population dynamics of target stemborers and leafrollers, and non-target planthoppers

The widespread planting of insect-resistant crops has caused a dramatic shift in agricultural landscapes, thus raising concerns about the potential impacts on both target and non-target pests. In this study, we examined the potential effects of intra-specific seed mixture sowing with transgenic Bt rice (Bt) and its parental non-transgenic line (Nt) (100% Bt rice [Bt₁₀₀ ], 5% Nt+95% Bt [Nt₀₅ Bt₉₅ ], 10% Nt+90% Bt [Nt₁₀ Bt₉₀ ], 20% Nt+80% Bt [Nt₂₀ Bt₈₀ ], 40% Nt+60% Bt [Nt₄₀ Bt₆₀ ] and 100% Nt rice [Nt₁₀₀ ]) on target and non-target pests in a 2-year field trial in southern China. The occurrence of target pests, Sesamia inferens, Chilo suppressalis and Cnaphalocrocis medinalis, decreased with the increased ratio of Bt rice, and the mixture ratios with more than 90% Bt rice (Bt₁₀₀ and Nt₀₅ Bt₉₅ ) significantly increased the pest suppression efficiency, with the lowest occurrences of non-target planthoppers, Nilaparvata lugens and Sogatella furcifera in Nt₁₀₀ and Nt₀₅ Bt₉₅ . Furthermore, there were no significant differences in 1000-grain dry weight and grain dry weight per 100 plants between Bt₁₀₀ and Nt₀₅ Bt₉₅ . Seed mixture sowing of Bt rice with ≤10% (especially 5%) of its parent line was sufficient to overcome potential compliance issues that exist with the use of block or structured refuge to provide most effective control of both target and non-target pests without compromising the grain yield. It is also expected that the strategy of seed mixture sowing with transgenic Bt rice and the non-transgenic parental line would provide rice yield stability while decreasing the insecticide use frequency in rice production.

Effects of seed mixture sowing with resistant and susceptible rice on population dynamics of target planthoppers and non-target stemborers and leaffolders

BACKGROUND

The widespread planting of insect-resistant crops has caused a dramatic shift in agricultural landscapes, thus raising concerns about the potential impact on both target and non-target pests worldwide. In this study, we examined the potential effects of six seed mixture ratios of insect-resistance dominance [100% (R100), 95% (S05R95), 90% (S10R90), 80% (S20R80), 60% (S40R60), and 0% (S100)] on target and non-target pests in a 2-year field trial in southern China.

RESULTS

The occurrence of the target pests Nilaparvata lugens and Sogatella furcifera decreased with an increase in the ratio of resistant rice, and mixture ratios with ≥90% resistant rice significantly increased the pest suppression efficiency, with the lowest occurrences of the non-target pests Sesamia inferens, Chilo suppressalis and Cnaphalocrocis medinalis for S100 and S10R90 seed mixture ratios. Furthermore, there were no significant differences in the 1000-grain dry weight and grain yield between R100 and other treatments with ≥80% resistant seeds in the mixture (S20R80, S10R90 and S05R95).

CONCLUSION

S10R90 produced a good yield and provided the most effective control of both target and non-target pests, with the potential to significantly reduce the application of chemical pesticides for integrated pest management in paddy fields. It is further presumed that the strategy of seed mixture with resistant and susceptible rice would be advantageous for rice yield stability. © 2018 Society of Chemical Industry.