Latest News on Entomology and Nematology : Nov 2020

Latest News on Entomology and Nematology : Nov 2020

Insecticide resistance in field populations of Asian citrus psyllid in Florida

BACKGROUND: Asian citrus psyllid (ACP), Diaphorina citri, is a major pest of citrus because it vectors the putative causal agent of huanglongbing disease. Insecticides are currently the basis of psyllid management programs, and the number of annual insecticide applications has increased significantly. In this paper, a series of investigations of insecticide resistance among field populations of adult and immature ACP in Florida is described.

RESULTS: In 2009, the highest level of resistance for adult ACP, as compared with the laboratory susceptible (LS) population, was found with imidacloprid with an LD50 resistance ratio (RR50) of 35 in one population. This was followed by chlorpyriphos (RR50 = 17.9, 13.3, 11.8 and 6.9), thiamethoxam (RR50 = 15 and 13), malathion (RR50 = 5.4 and 5.0) and fenpropathrin (RR50 = 4.8). In 2010, mortality of adults from all five sites sampled was lower than with the LS population at three diagnostic concentrations of each insecticide tested. Among nymph populations, indications of resistance were observed with carbaryl (RR50 = 2.9), chlorpyriphos (RR50 = 3.2), imidacloprid (RR50 = 2.3 and 3.9) and spinetoram (RR50 = 4.8 and 5.9). General esterase, glutathione S‐transferase and monooxygenase levels were also elevated in field‐collected adult and nymph ACP as compared with the LS population.

CONCLUSION: The present results suggest that varying levels of insecticide susceptibility exist in ACP populations across the citrus‐growing areas of Florida. Increased levels of detoxifying enzymes in these populations may partially explain these differences. The present results indicate that insecticide resistance may become an emerging problem for ACP control if effective resistance management is not practiced. [1]

Nicotinoid and pyrethroid insecticide resistance in houseflies (Diptera: Muscidae) collected from Florida dairies

BACKGROUND: The housefly, Musca domestica L., continues to be a major pest of confined livestock operations. Houseflies have developed resistance to most chemical classes, and new chemistries for use in animal agriculture are increasingly slow to emerge. Five adult housefly strains from four Florida dairy farms were evaluated for resistance to four insecticides (beta‐cyfluthrin, permethrin, imidacloprid and nithiazine).

RESULTS: Significant levels of tolerance were found in most field strains to all insecticides, and in some cases substantial resistance was apparent (as deduced from comparison with prior published results). At the LC90 level, greater than 20‐fold resistance was found in two of the fly strains for permethrin and one fly strain for imidacloprid. Beta‐cyfluthrin LC90 resistance ratios exceeded tenfold resistance in three fly strains. The relatively underutilized insecticide nithiazine had the lowest resistance ratios; however, fourfold LC90 resistance was observed in one southern Florida fly strain. Farm insecticide use and its impact on resistance selection in Florida housefly populations are discussed.

CONCLUSION: Housefly resistance to pyrethroids is widespread in Florida. Imidacloprid resistance is emerging, and tolerance was observed to both imidacloprid and nithiazine. If these insecticides are to retain efficacy, producer use must be restrained. [2]

Antifeedant and sublethal effects of imidacloprid on Asian citrus psyllid, Diaphorina citri

BACKGROUND: Asian citrus psyllid (ACP), Diaphorina citri Kuwayama, transmits the causal bacteria of the devastating citrus disease huanglongbing (HLB). Because of the variation in spatial and temporal uptake and systemic distribution of imidacloprid applied to citrus trees and its degradation over time in citrus trees, ACP adults and nymphs are exposed to concentrations that may not cause immediate mortality but rather sublethal effects. The objective of this laboratory study was to determine the effects of sublethal concentrations of imidacloprid on ACP life stages.

RESULTS: Feeding by ACP adults and nymphs on plants treated daily with a sublethal concentration (0.1 µg mL−1) of imidacloprid significantly decreased adult longevity (8 days), fecundity (33%) and fertility (6%), as well as nymph survival (12%) and developmental rate compared with untreated controls. The magnitude of these negative effects was directly related to exposure duration and concentration. Furthermore, ACP adults that fed on citrus leaves treated systemically with lethal and sublethal concentrations of imidacloprid excreted significantly less honeydew (7–94%) compared with controls in a concentration‐dependent manner suggesting antifeedant activity of imidacloprid.

CONCLUSIONS: Sublethal concentrations of imidacloprid negatively affect development, reproduction, survival and longevity of ACP, which likely contributes to population reductions over time. Also, reduced feeding by ACP adults on plants treated with sublethal concentrations of imidacloprid may potentially decrease the capacity of ACP to successfully acquire and transmit the HLB causal pathogen. [3]

Preliminary Ecological Studies of Insect Species Associated with Different Accessions of Eggplant (Solanum melongena L.) in Southern Ghana

Aims: To determine the relative abundance and diversity of insects on twenty-two accessions of eggplants, as a guide to instituting control measures against unacceptable damage of egg plants grown under field conditions in the Coastal Savannah agro-ecological zone of Ghana.

Study Design: The experimental treatments were deployed in a Randomized Complete Block Design (RCBD), replicated three times.

Place and Duration of Study: Nuclear Agriculture Research Center (NARC) farms and the laboratories of Radiation Entomology and Pest Management Center (REPMC) of Biotechnology and Nuclear Agriculture Research Institute (BNARI), between September 2012 and November 2012.

Methodology: The fields were divided into three replicates each containing twenty-two different accessions of eggplant S. macrocarpon, S. gilio GH8769, S. aethiopicum, S. gilio GH8771,  Nroroye F, Ntorewa K, S. gilio GH8770, S. melongena GH 3949, Ntropo B, Ndroshye E, Ndroshye C, Ndroshye, Nroroye A, Black beauty, Nroroye G, Ntropo K, Ntropo I, Sammy, Ntropo G, Nroroye D, Ntropo H, Nroroye J. The seeds were sown in a nursery and transplanted 35 days after germination to an experimental plot measuring 40 m x 11.4 m in the centre of one acre area so that the experimental plot was surrounded by a homogeneously managed terrain. The experimental treatments were deployed in a Randomized Complete Block Design (RCBD), replicated three times. Each replicate was allotted a plot size of 19.8 m x 8.4 m. Each sub-plot planted to one accession consisting of 22 plants at a spacing of 0.9 m x 0.6 m. Plots were separated by a distance of 2 m. Random sampling technique was used on weekly basis to study the relative abundance, diversity and behaviour of the insect species on the accessions.

Results: Fifteen different insect species were identified on the twenty two accessions of eggplant from the vegetative through to the maturity stage. These comprised three beneficial insects (C. lunata, Camponotus sp. and M. religiosa) and twelve pests (A. craccivora, B. tabaci, B. invadens, Dysdercus sp., G. compestris, L. orbonalis, P. mali, Podagrica sp., O. virudulus, N. viridulus, Phenacoccus sp. and Z. variegatus). Their relative abundance ranged from 0.20– 8.78% for beneficial insects and 0.03 – 45.63% for pests. The highest abundance of insects were found on the accessions Ndroshye (14.09%) and Nroroye G (9.80%). Nroroye F registered the highest diversity of insect species, while Ntropo B and Sammy recorded the least diversity.

Conclusion: There was high abundance of insect species (65.85%) on the field of study. High diversity of insect species was noted and this could be a guide in instituting control measure before pest numbers go beyond the economic thresh-hold level. [4]

Comparative Effects of Piper guineense Emulsion and Cabbage-Tomato Intercropping for Controlling Cabbage Pests and Improving Performance

Aim: To improve cabbage production by controlling cabbage pests using locally produced organic pesticide and cabbage-tomato intercropping.

Methodology: Four treatments (control, cabbage-tomato intercropping, organic and synthetic pesticides) were evaluated for their potential to control cabbage pests and improve performance.

Results: Cabbage pest infestation correlated negatively with treatments (r = −0.95), ranging from 2–23 infested plants across treatments that differed (P = .001) significantly, with highest in control compared to other treatments (P = .05). Diamondback moth ranged from 1–10 per plant and differed (P = .001) significantly across treatments, with highest in control compared to other treatments (P = .05). Looper larvae correlated negatively with treatments (r = −0.62), ranging from 0–8 per plant and differed (P = .05) significantly across treatments, with highest in control compared to other treatments (P = .05). Snails ranged from 34–91 per treatment and differed (P = .001) significantly across treatments, with highest in control and lowest in organic compared to other treatments (P = .05). The number of sprouted cabbage plants ranged from 0–5 per treatment and differed (P = .001) significantly across treatments, with highest in control compared to other treatments (P = .05). Sprouted cabbage correlated negatively with treatments (r= −0.93) and correlated positively with pest infestation (r = 0.81), diamondback moth (r = 0.71) and looper (r= 0.58). Cabbage yield ranged from 3.2–6.0 t ha-1 and differed (P = .05) significantly across treatments with the lowest in control and highest in intercropping (P = .05). Cabbage yield correlated negatively with diamondback moth (r = −0.62), looper (r = −0.63) and sprouted cabbage (r = −0.62).

Conclusion: Piper emulsion and intercropping effectively controlled cabbage pests while intercropping additionally increased cabbage yield. [5]

Reference

[1] Tiwari, S., Mann, R.S., Rogers, M.E. and Stelinski, L.L., 2011. Insecticide resistance in field populations of Asian citrus psyllid in Florida. Pest management science, 67(10), pp.1258-1268.

[2] Kaufman, P.E., Nunez, S.C., Mann, R.S., Geden, C.J. and Scharf, M.E., 2010. Nicotinoid and pyrethroid insecticide resistance in houseflies (Diptera: Muscidae) collected from Florida dairies. Pest Management Science: formerly Pesticide Science, 66(3), pp.290-294.

[3] Boina, D.R., Onagbola, E.O., Salyani, M. and Stelinski, L.L., 2009. Antifeedant and sublethal effects of imidacloprid on Asian citrus psyllid, Diaphorina citri. Pest Management Science: formerly Pesticide Science, 65(8), pp.870-877.

[4] Kofi Ofori, E. S., Afful, N., Quartey, E., Osae, M. and Amoatey, H. (2015) “Preliminary Ecological Studies of Insect Species Associated with Different Accessions of Eggplant (Solanum melongena L.) in Southern Ghana”, Journal of Agriculture and Ecology Research International, 4(4), pp. 199-210. doi: 10.9734/JAERI/2015/20475.

[5] Tanyi, C., Ngosong, C. and Ntonifor, N. (2018) “Comparative Effects of Piper guineense Emulsion and Cabbage-Tomato Intercropping for Controlling Cabbage Pests and Improving Performance”, Journal of Agriculture and Ecology Research International, 13(4), pp. 1-12. doi: 10.9734/JAERI/2017/38815.

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