Better outcomes for pest pressure, insecticide use, and yield in less intensive agricultural landscapes.

Agricultural systems have been continuously intensified to meet rising demand for agricultural products. However, there are increasing concerns that larger, more connected crop fields and loss of seminatural areas exacerbate pest pressure, but findings to date have been inconclusive. Even less is known about whether increased pest pressure results in measurable effects for farmers, such as increased insecticide use and decreased crop yield. Using extensive spatiotemporal data sampled every 2 to 3 d throughout five growing seasons in 373 cotton fields, we show that pests immigrated earlier and were more likely to occur in larger cotton fields embedded in landscapes with little seminatural area (<10%). Earlier pest immigration resulted in earlier spraying that was further linked to more sprays per season. Importantly, crop yield was the lowest in these intensified landscapes. Our results demonstrate that both environmental conservation and production objectives can be achieved in conventional agriculture by decreasing field sizes and maintaining seminatural vegetation in the surrounding landscapes.

Exposure to polylactic acid induces oxidative stress and reduces the ceramide levels in larvae of greater wax moth (Galleria mellonella).

Plastic biodegradation by insects has made significant progress, opening up new avenues for the treatment of plastic waste. Wax moth larvae, for example, have attracted the attention of the scientific community because they are known to chew, ingest, and biodegrade natural polymer bee waxes. Despite this, we know very little about how these insects perform on manufactured plastics or how manufactured plastics affect insect metabolism. As a result, we studied the metabolism of greater wax moths (Galleria mellonella) fed on molasses-supplemented polylactic acid plastic (PLA) blocks. An analysis of the central carbon metabolism (CCM) metabolites was performed using liquid chromatography triple quadrupole mass spectrometry (LC-QQQ-MS), while an analysis of untargeted metabolites and lipids was conducted using liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QToF-MS). In total, 169 targeted CCM metabolites, 222 untargeted polar metabolites, and 196 untargeted nonpolar lipids were identified within the insect samples. In contrast, compared to control larvae, PLA-fed larvae displayed significantly different levels of 97 CCM metabolites, 75 polar metabolites, and 57 lipids. Purine and pyrimidine metabolisms were affected by PLA feeding, as well as amino acid metabolism, carbohydrates, cofactors, vitamins, and related metabolisms. Additionally, PLA exposure disrupted insect energy metabolism and oxidative stress, among other metabolic disturbances. The larvae fed PLA have lower levels of several lipids, suggesting a reduction in lipid reserves, and ceramide levels are likely to have changed due to apoptosis and inflammation. The study indicates that G. mellonella larvae could ingest PLA but this process causes some metabolic stress for the host. Future studies of the molecular pathways of this biodegradation process might help to provide strategies for stress reduction that would speed up insect digestion of plastic.

Is there any biological insight (or respite) for insects exposed to plastics? Measuring the impact on an insects central carbon metabolism when exposed to a plastic feed substrate.

Insects used to treat organic waste streams and produce valuable protein products are increasingly exposed to plastic contaminated source material assimilating plastic carbon into organic biomass, which is pervasive and hazardous to organisms. Our understanding of this increased insect-plastic interaction remains limited and needs urgent scientific attention if plastic biodegradation and production rates of quality protein are to be improved. Herein, we investigated the biochemical impact of various plastics using three insect models. Black Soldier Fly (BSF), Mealworm (MW), and Wax Moth (WM) larva were each exposed to a plastic substrate (PET, PE, PS, Expanded PE, PP, and PLA) as the primary carbon source for five days to explore any positive metabolic benefits in terms of insect performance and plastic degradation potential. Central carbon metabolism (CCM) metabolites were analyzed via a targeted tMRM liquid chromatography triple quadrupole mass spectrometry (LC-QqQ-MS) method. Unique expressed pathways were observed for each insect model. When reared on PET, BSF larvae were found to have an elevated pyrimidine metabolism, while the purine metabolism pathway was strongly expressed on other plastics. BSF also exhibited a downregulated Vitamin B6 metabolism across all plastics, indicating a likely gut-symbiont breakdown. The MW and WM model insects were metabolically more active on PLA and expanded foam plastics. Further, WM exhibited an elevation in Vitamin B6 metabolism. This data suggests a positive insect-specific interaction towards certain plastic types that warrants further investigation. It is anticipated that through deeper insight into the metabolic impact and benefits afforded from certain plastics, an insect biotransformation pipeline can be established that links fit-for-purpose insect models to individual plastic types that address our growing plastic waste issue.

Within-Season Changes in Land-Use Impact Pest Abundance in Smallholder African Cassava Production Systems.

Cassava (Manihot esculenta Crantz), an important commercial and food security crop in East and Central Africa, continues to be adversely affected by the whitefly Bemisia tabaci. In Uganda, changes in smallholder farming landscapes due to crop rotations can impact pest populations but how these changes affect pest outbreak risk is unknown. We investigated how seasonal changes in land-use have affected B. tabaci population dynamics and its parasitoids. We used a large-scale field experiment to standardize the focal field in terms of cassava age and cultivar, then measured how Bemisia populations responded to surrounding land-use change. Bemisia tabaci Sub-Saharan Africa 1 (SSA1) was identified using molecular diagnostics as the most prevalent species and the same species was also found on surrounding soybean, groundnut, and sesame crops. We found that an increase in the area of cassava in the 3-7-month age range in the landscape resulted in an increase in the abundance of the B. tabaci SSA1 on cassava. There was a negative relationship between the extent of non-crop vegetation in the landscape and parasitism of nymphs suggesting that these parasitoids do not rely on resources in the non-crop patches. The highest abundance of B. tabaci SSA1 nymphs in cassava fields occurred at times when landscapes had large areas of weeds, low to moderate areas of maize, and low areas of banana. Our results can guide the development of land-use strategies that smallholder farmers can employ to manage these pests.

Improving climate suitability for Bemisia tabaci in East Africa is correlated with increased prevalence of whiteflies and cassava diseases.

Projected climate changes are thought to promote emerging infectious diseases, though to date, evidence linking climate changes and such diseases in plants has not been available. Cassava is perhaps the most important crop in Africa for smallholder farmers. Since the late 1990's there have been reports from East and Central Africa of pandemics of begomoviruses in cassava linked to high abundances of whitefly species within the Bemisia tabaci complex. We used CLIMEX, a process-oriented climatic niche model, to explore if this pandemic was linked to recent historical climatic changes. The climatic niche model was corroborated with independent observed field abundance of B. tabaci in Uganda over a 13-year time-series, and with the probability of occurrence of B. tabaci over 2 years across the African study area. Throughout a 39-year climate time-series spanning the period during which the pandemics emerged, the modelled climatic conditions for B. tabaci improved significantly in the areas where the pandemics had been reported and were constant or decreased elsewhere. This is the first reported case where observed historical climate changes have been attributed to the increase in abundance of an insect pest, contributing to a crop disease pandemic.

Spatio-Temporal Variation in Landscape Composition May Speed Resistance Evolution of Pests to Bt Crops.

Transgenic crops that express insecticide genes from Bacillus thuringiensis (Bt) are used worldwide against moth and beetle pests. Because these engineered plants can kill over 95% of susceptible larvae, they can rapidly select for resistance. Here, we use a model for a pyramid two-toxin Bt crop to explore the consequences of spatio-temporal variation in the area of Bt crop and non-Bt refuge habitat. We show that variability over time in the proportion of suitable non-Bt breeding habitat, Q, or in the total area of Bt and suitable non-Bt habitat, K, can increase the overall rate of resistance evolution by causing short-term surges of intense selection. These surges can be exacerbated when temporal variation in Q and/or K cause high larval densities in refuges that increase density-dependent mortality; this will give resistant larvae in Bt fields a relative advantage over susceptible larvae that largely depend on refuges. We address the effects of spatio-temporal variation in a management setting for two bollworm pests of cotton, Helicoverpa armigera and H. punctigera, and field data on landscape crop distributions from Australia. Even a small proportion of Bt fields available to egg-laying females when refuges are sparse may result in high exposure to Bt for just a single generation per year and cause a surge in selection. Therefore, rapid resistance evolution can occur when Bt crops are rare rather than common in the landscape. These results highlight the need to understand spatio-temporal fluctuations in the landscape composition of Bt crops and non-Bt habitats in order to design effective resistance management strategies.

Wind-borne dispersal of a parasitoid: the process, the model, and its validation.

The aphelinid parasitoid Eretmocerus hayati Zolnerowich & Rose (Hymenoptera: Aphelinidae) was recently released in Australia as a biocontrol agent against the crop pest Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae). It was found that the parasitoid can spread over several kilometers in a single generation and continue laying eggs for over a fortnight. A simple wind-advection model was fitted to emergence data from a first release between Fassifern and Kalbar, Queensland, and its predictive ability was tested against the second release near Carnarvon, Western Australia. The fitting of the model was used to develop several hypotheses about the dispersal of E. hayati, which were validated by the second release: E. hayati flies in the same direction as the wind to a distance proportional to the wind speed; this wind-borne flight takes place at any time during daylight hours; a flight is attempted every day after emergence unless there are high wind conditions during that day; and the high wind condition that will delay flight is wind speeds in excess of ≍2 m/s. This model of E. hayati dispersal may be contrasted with previous models fitted for Eretmocerus species, for which dispersal was dominated by diffusion processes, and parasitoid spread was constrained to the scales of tens and hundreds of meters.