Tri-trophic interactions between Bt cotton, the herbivore Aphis gossypii Glover (Homoptera: Aphididae), and the predator Chrysopa pallens (Rambur) (Neuroptera: Chrysopidae)

Predation evaluation of the green lacewing, Chrysopa pallens on the pink tea mite pest, Acaphylla theae (Watt) (Acarina: Eriophyidae)

A better understanding of predator-prey interactions is crucial for the development of biological control strategies. The green lacewing, Chrysopa pallens, is a well-known generalist predator and reportedly functions as one of the most important biological control agents of insect pests. However, information regarding C. pallens' predation on tea plant pests, particularly notorious tea mites, remains largely unknown. In this study, we focused on the predator-prey relationship between C. pallens and an important tea mite pest, Acaphylla theae. We designed species-specific primers for the detection of A. theae DNA and established a PCR-based DNA gut content analysis assay. These results demonstrated that the primers were A. theae-specific and suitable for its molecular identification. The laboratory feeding experiment showed that the detectability success (DS50) of A. theae DNA remaining in C. pallens' guts was 2.9 h. We then performed a molecular detection of field predation, and achieved a 23.53% positive detection rate of A. theae DNA in the guts of field-collected C. pallens. This, for the first time, provides direct evidence that C. pallens can prey on A. theae in tea plantations. Finally, we tested the prey preference and estimated the predation ability of C. pallens on different developmental stages of A. theae. The results revealed that C. pallens had no significant preference for different developmental stages of A. theae. The functional responses of C. pallens' predation on different densities of A. theae at different developmental stages followed a Type II Holling model. The initial attack rate (a') ranged from 0.735 to 0.858 and the handling time (Th) was approximately 0.01. This study is the first to demonstrate the trophic interactions between C. pallens and A. theae and provides evidence for the development of biological control strategies against A. theae using C. pallens as a candidate predator.

Transgenic Cry1Ac cotton does not affect the development and fecundity of Chrysoperla carnea

The development and fecundity of the predator Chrysoperla carnea Stephens (Neuroptera: Chrysopidae) were assessed by feeding Aphis gossypii Glover (Hemiptera: Aphididae) that had been reared on transgenic Bacillus thuringiensis (Bt) cotton SGK321 and a non-Bt cotton control (SY321) for two successive generations. We found no significant differences in the developmental stage duration, stage survival, or egg hatch rate between C. carnea fed A. gossypii reared on the Bt and non-Bt cotton. The fecundity per female over a 25-day observation period was very similar between treatments; for C. carnea fed A. gossypii reared on SGK321 vs. SY321, the amount of eggs laid was not significantly different in both generations. Furthermore, a population dynamics of A. gossypii and lacewing (mainly C. carnea) were highly similar in the SGK321 and SY321 treatments during 2016–2017. These results suggest that Bt cotton does not have a significantly negative or positive effect on C. carnea in terms of development, survival, fecundity, or population dynamics.

Insect-resistant biotech crops and their impacts on beneficial arthropods

With a projected population of 10 billion by 2050, an immediate priority for agriculture is to achieve increased crop yields in a sustainable and cost-effective way. The concept of using a transgenic approach was realized in the mid-1990s with the commercial introduction of genetically modified (GM) crops. By 2010, the global value of the seed alone was US $11.2 billion, with commercial biotech maize, soya bean grain and cotton valued at approximately US $150 billion. In recent years, it has become evident that insect-resistant crops expressing δ-endotoxin genes from Bacillus thuringiensis have made a significant beneficial impact on global agriculture, not least in terms of pest reduction and improved quality. However, because of the potential for pest populations to evolve resistance, and owing to lack of effective control of homopteran pests, alternative strategies are being developed. Some of these are based on Bacillus spp. or other insect pathogens, while others are based on the use of plant- and animal-derived genes. However, if such approaches are to play a useful role in crop protection, it is desirable that they do not have a negative impact on beneficial organisms at higher trophic levels thus affecting the functioning of the agro-ecosystem. This widely held concern over the ecological impacts of GM crops has led to the extensive examination of the potential effects of a range of transgene proteins on non-target and beneficial insects. The findings to date with respect to both commercial and experimental GM crops expressing anti-insect genes are discussed here, with particular emphasis on insect predators and parasitoids.

Carabidae population dynamics and temporal partitioning: response to coupled neonicotinoid-transgenic technologies in maize

Insecticidal Bt crops and seed treatments represent additional pest management tools for growers, prompting ecological studies comparing their impact on farm system inputs and effects to nontarget organisms compared with conventional practices. Using high taxonomic and temporal resolution, we contrast the dominance structure of carabids and dynamics of the most abundant species in maize (both sweet and field corn) agroecosystems using pest management tactics determined by the purchase of seed and application of pyrethroid insecticides. In the seed-based treatments, sweet corn contained Cry1Ab/c proteins, whereas field corn contained the coupled technology of Cry3Bb1 proteins for control of corn rootworm and neonicotinoid seed treatments aimed at secondary soil-borne pests. The insecticide treatments involved foliar pyrethroids in sweet corn and at-planting pyrethroids in field corn. The carabid community, comprised of 49 species, was dominated by four species, Scarites quadriceps Chaudoir, Poecilus chalcites Say, Pterostichus melanarius Illiger, and Harpalus pensylvanicus DeGeer, that each occupied a distinct temporal niche during the growing season. Two species, Pt. melanarius and H. pensylvanicus, exhibited differences between treatments over time. Only H. pensylvanicus had consistent results in both years, in which activity densities in field corn were significantly higher in the control in July and/or August. These results, along with laboratory bioassays, led us to hypothesize that lower adult captures resulted from decrease in prey availability or exposure of H. pensylvanicus larvae to soil-directed insecticides-either the neonicotinoid seed treatment in the transgenic field corn or an at-planting soil insecticide in the conventional field corn.