Early Instars Research Articles

Toxicity and histological architecture of <i>Semecarpus anacardium </i>kernel extract on the foregut of <i>Heliothis armigera </i>

The efficacy of Semecarpus anacardium Linn. kernel extract in chloroform as an antifeedant and stomach poison agent was assessed against Heliothis armigera (Hubner) early fourth instars. Larvae that were fed with food containing different doses of extract showed antifeedant, toxic effects and decreased consumption. The foregut histopathological architecture of larvae fed with S. anacardium kernel extract in chloroform at concentration equal to LD50 value and after 24 and 96 hours of treatment, demonstrates substantial injury to the epithelium layer, including vacuolization in some areas, gut tissue shrinkage, and peritrophic membrane disruption, which leads to the degeneration of goblet, regenerative, and epithelial cells. The height of the columnar epithelium and diameter of lumen were also reduced after 24 hours of exposure. These alterations in the gut had a detrimental effect on the larvae’s ability to digest and absorb food, resulting to a nutritional deficit that may have stunted their development. The findings of this study indicate that S. anacardium kernel extracts in chloroform have a significant stomach poisoning capability against H. armigera larvae, suggesting that this approach could be investigated as an environmentally safe method of integrated pest management.

Impact of short‐ and long‐duration thermal stress on antioxidant enzyme activity in Parthenium beetles

AbstractInsects encounter variable temperature conditions in their natural habitats. Under non‐optimal temperatures, they experience thermal stress and oxidative damage, which are mitigated by antioxidant enzymes like superoxide dismutase (SOD), catalase (CAT) and lipid peroxidation (LPO). While short‐term effects of thermal stress on antioxidant enzyme activities in insects are well understood, the long‐term effects are less explored. We investigated both short‐term (3 and 6 h) and long‐term (24 h) effects of thermal stress on SOD, CAT and LPO activities in the Parthenium beetle, Zygogramma bicolorata Pallister at cold (15°C), control/optimal (25°C) and hot (35°C) temperatures. Although Z. bicolorata is an effective biocontrol agent for noxious Parthenium weed, no prior study assessed the impact of thermal stress on antioxidant enzyme activities in this beetle. Our results revealed that antioxidant enzymes activities increased above control levels in both larvae and adults when exposed to thermal stress for short durations. Under long‐term thermal stress, CAT and LPO activities decreased below control levels, while SOD activity increased. Regardless of temperature conditions, early larval instars exhibited higher enzyme activities compared to later instars. In adults, males showed higher SOD and CAT activities, whereas LPO activity did not differ significantly between sexes. Our findings suggest that short‐term thermal stress can stimulate protective enzyme activity in these beetles and help them adapt to suboptimal temperatures. However, prolonged exposure may lead to excessive stimulation, potentially inhibiting protective enzyme activity and causing the beetles to activate alternative pathways to manage thermal stress. Moreover, fourth instars and adult females are the most thermal stress‐tolerant stages for Parthenium biocontrol.

Assessment of multifunctional activity of graphene oxide and guar gum-based nanomaterials against Aedes aegypti

Nanomaterials have been receiving much research attention in controlling insect pests and vectors. Properties, such as small surface-to-volume ratio, low dosages, durability, solubility, enhanced target activity, pore size and surface characteristics have enabled the design of precise and targeted insecticides through adsorption, encapsulation, and conjugation. The reported study aims to evaluate the efficacy of graphene oxide (GO) and guar gum (GG)-based nanomaterials against early fourth instar of Aedes aegypti, a mosquito responsible for transmitting diseases like dengue fever, Zika virus, and chikungunya, among many others. GO and a total of eight nanomaterials (SA-1 to SA-8) were formulated using GO, GG and their combinations with ferrous oxide and copper oxide. Each material was characterized using various biophysical techniques. The materials were evaluated for larvicidal potential by assessing their efficacy on the survival and morphology of Ae. aegypti, while the contact irritancy activity focused on determining their irritant properties upon direct exposure to the female adults. The larvicidal and irritant bioassays, conducted with these nanomaterials at different concentrations, demonstrated concentration-dependent mortality and significant behavioral responses. The exposures with nanomaterials also resulted in a deposition of black soot on the larval cuticle. The most effective nanomaterial was found as ferrous oxide nanomaterial which induced 100% larval mortality as well as significant contact irritancy. The results indicate the potential use of GO and GG-based nanomaterials against Ae. aegypti after concentration optimization.

Effects of fasting on the interplay between temperature and Trypanosoma cruzi infection on the life cycle of the Chagas disease vector Rhodnius prolixus.

Rhodnius prolixus, a triatomine insect, is one of the most important vectors of Chagas disease in South America. Its interaction with the parasite Trypanosoma cruzi, the causative agent of this disease, is known to be deeply affected by ambient temperature and the nutritional status of the insect vector. In this study, we investigated how starvation affects the life cycle of R. prolixus and the population dynamics of the parasite inside the intestine of the vector at four temperatures ranging from 24°C to 30°C. The weights and molting times of chronically infected and uninfected insects were monitored through repeated 30-day fasting periods from first instar to adult stage, assessing their capacity to retain blood meal weight between developmental stages and tracking parasite concentrations in their urine. Our results demonstrate that ambient temperature is a crucial factor affecting the resistance of R. prolixus to starvation, as survival, body weight, and weight retention greatly decreased in high temperature treatments. Furthermore, we showed that temperature significantly influenced whether T. cruzi established an infection in early instars, with few insects developing infections at the lowest and highest temperature treatments. Additionally, we discovered that a fasting period of 30 days induces a steady decrease in parasite populations in the vector over its lifetime. Infection by T. cruzi had no effect on the survival, molting time, and nutritional factors monitored in our protocol. Our results highlight the importance of nutrition as a determining factor for the development of the vector and the parasite, providing valuable insights for elucidating the complex interplay between temperature and nutrition in shaping the epidemiology of Chagas disease in a changing climate.

A new genus and species of Paranthrenini from Angola (Lepidoptera: Sesiidae).

A new genus and species, Afranthrene cinerea gen. & sp. nov., from Angola is described and depicted. The new genus belongs to the Adixoa Hampson, [1893] genera group and is related to the African genera Fortikona Bartsch & Sáfián, 2023, Rubukona Fischer, 2007 and Thyranthrene Hampson, 1919. The female, early instars and host plant of the new species are unknown.

A retrospective analysis on the effects of climate warming on the pine processionary moth at the southern edge of its range

Ectotherms are largely impacted by extreme climate events, essentially heatwaves. In Tunisia, the pine processionary moth (PPM), Thaumetopoea pityocampa, is a defoliator typically laying eggs in summer. Its geographical range is expanding northwards in Europe while retracting from southern Tunisia where summer temperatures can reach extreme heats. We explored the effects of climate change over the last 30 years on PPM at its southern range edge. We investigated variations of fecundity and causes of egg mortality over time using historical and contemporary collections of egg masses. Due to incomplete historical series, a clustering method was used to group climatically homologous sampling sites and perform allochronic analyses on clusters instead of individual localities. Our results suggest negative effects of summer heat on egg survival, down to 0% hatching rate in one site during a major heatwave. Such high hatching failures resulted partly from high egg sterility and aborted embryos, with little effects of parasitism rate, suggesting heat susceptibility during embryonic development, but our results do not allow distinguishing impeded mating success from failed egg maturation or early embryo death. Decreasing female fecundity was observed in regions where allochronic comparisons were possible, associated with a decrease in parasitism rate, while climatic variability increased. Previous studies have confirmed experimentally the thermal sensitivity of PPM early instars to temperatures observed in the present work, including one population from southern Tunisia. However, further work is required to evaluate the relative importance of warming summers among populations, since the risk of heat stress depends on the phenology of sensitive instars, and populations from the warmest areas may not necessarily be the most vulnerable to climate change if they already evolved phenological heat avoidance. In addition to heat‐induced mortality, the ultimate fitness of heat survivors should also be explored to determine potential carry‐over effects on subsequent life stages.

Reproductive Biology and Rearing Improvements of Apanteles opuntiarum, Potential Biocontrol Agent of the Argentine Cactus Moth, Cactoblastis cactorum.

The cactus moth, Cactoblastis cactorum (Berg) (Lepidoptera: Pyralidae) is native to South America and has been used as a biocontrol agent of Opuntia (Cactaceae) in Australia and South Africa. Its invasion in North America has raised concerns for the native Opuntia in the USA and Mexico. We investigated the reproductive biology and rearing procedures of a host-specific potential biocontrol agent, Apanteles opuntiarum Martínez and Berta (Hymenoptera: Braconidae). Given the gregarious nature of the parasitoid larvae, we studied the morphology of the immature stages and evaluated evidence of polyembryony and superparasitism. We also investigated the effects of host exposure arena and host density on parasitism rates and wasp production. The morphological descriptions provide a basis for comparison with other species. Early larval instars of A. opuntiarum are similar to other microgastrine immature stages. However, the mature larva exhibits placoid sensilla in the epistomal region, a unique character not previously reported. We provide evidence that A. opuntiarum eggs are not polyembryonic; females frequently superparasitize and have an oviposition preference for larvae parasitized 1-2 d previously. Exposing larvae of C. cactorum to wasps while inside the cactus resulted in lower parasitism and fewer offspring from each host than exposing larvae in the arena without the cactus. Parasitism and mortality rates were higher at lower host densities, possibly due to reduced host group defensive behavior. These results suggest that preference for superparasitism, host defensive behavior, and interactions with the cactus may play an important role in per-host wasp production under laboratory conditions.

The cultivable gut bacteria Enterococcus mundtii promotes early-instar larval growth of Conogethes punctiferalis via enhancing digestive enzyme activity.

Gut bacteria are crucial in influencing insect development and even phenotypic plasticity. The yellow peach moth Conogethes punctiferalis, as a significant borer pest, has been the subject of limited reports regarding the structural and diversification changes in its gut microbiota during feeding, and their potential impacts on the growth and development of the host insects. This study, employing 16S rRNA sequencing, demonstrates distinct shifts in the larvae gut microbiome of C. punctiferalis between different feeding stages, highlighting a pronounced diversity in the early-instar with Enterococcus as a predominant genus in laboratory populations. Through in vitro cultivation and sequencing, three bacterial strains - Micrococcus sp., Brevibacterium sp. and Enterococcus mundtii - were isolated and characterized. Bioassays revealed that E. mundtii-infused corn significantly boosts early-instar larval growth, enhancing both body length and weight. Quantitative PCR and spectrophotometry confirmed a higher abundance of E. mundtii in younger larvae, correlating with increased digestive enzyme activity and total protein levels. This study reveals the heightened gut microbiota diversity in early instars of C. punctiferalis larvae, highlighting that Enterococcus represent a predominant bacteria in laboratory populations. In vitro cultivation and bioassays unequivocally demonstrate the significant role of the cultivable gut bacteria E. mundtii in promoting the growth of early-instar larva. These findings provide a solid theoretical foundation for advancing the comprehension of the intricate interactions between gut microbiota and insect hosts, as well as for the development of eco-friendly pest control technologies based on targeted manipulation of insect gut microbial communities. © 2024 Society of Chemical Industry.

Efficacy of sugar‐protein non‐membranous dietary system for diapause egg production in Aedes albopictus mosquitoes under short‐day conditions

AbstractThe Asian tiger mosquito, Aedes albopictus (Skuse) (Diptera: Culicidae), is a global vector of dengue, chikungunya and zika viruses. With extreme adaptability of survival as diapause eggs, this mosquito has invaded and established in temperate climatic zones. The diapause eggs are specially programmed to overcome the harsh winter conditions in temperate habitats. In the laboratory, diapausing females are reared from early larval instars under short‐day conditions (21°C and 16D:8 L photoperiods). Aedes albopictus is normally fed on Guinea pigs for the rearing of diapause mosquitoes which requires ethical approval from the animal use committee and costly arrangements. Therefore, the present study was conducted to find whether bovine serum albumin protein (10%) with sucrose (5%) solution (SAP‐10) offered through a membrane‐free feeding system would result in an alternative diet for the production of diapause eggs in comparison to blood‐feeding. This feeding system shows a considerable rate of engorgement of diapausing females under short‐day conditions and produced 30.8 diapause eggs/female in comparison to blood‐feeding on a guinea pig (40.9 eggs/female). The diapause rate of viable eggs for the SAP‐10 diet (95.28%) was similar to the blood‐feeding (96.32%). The findings suggest that the present diet feeding system is a promising tool for the rearing of diapause Ae. albopictus mosquitoes under short‐day conditions. Further studies are suggested to evaluate the physiological and developmental aspects of mosquitoes reared on the diet.

Predation efficacy of Chrysoperla carnea on two economically important stink bugs

Larvae of the green lacewing Chrysoperla carnea (Stephens) (Neuroptera: Chrysopidae) are generalist predators feeding on a range of pests in agroecosystems. Little is known about the suitability of stink bugs as prey for lacewing larvae. In the present laboratory study, the predatory efficacy of C. carnea on two economically important stink bugs, Halyomorpha halys (Stål) and Nezara viridula (L.) (Hemiptera: Pentatomidae), was evaluated at three constant temperatures (16, 21, and 26 °C) in different arenas (10-cm diameter dishes with bean pod slices or caged small bean plants). We found that second and third instars of C. carnea readily prey on the first instars of both stink bug species. However, only third instars of C. carnea could successfully kill and feed on second instars of either pentatomid. The complexity of the arena, as well as the life stage of the prey and predator influenced the predation efficacy of C. carnea on stink bug nymphs, whereas temperature did not. The observed predation rates on the early instars of both stink bugs suggest that augmentative releases of C. carnea larvae may have some potential in greenhouse crops, particularly against N. viridula infestations, whereas in open field crops their natural populations may also contribute to pest suppression within the broader predator guild.

Cross-instar larval identification leads divergent decision on pest management: An example from white grubs on peanuts

Accurate larval identification is a prerequisite for integrated pest management, but remains a long-term difficulty in insect taxonomy. Previous descriptions are mainly focused on the most disruptive final instar larvae. However, earlier instars especially cross-instar larval morphological comparisons were rarely delivered hitherto. Polyphylla laticollis and Maladera orientalis are pests that damage peanut crops at various developmental stages. The first instar larvae of P. laticollis and the mature larvae of M. orientalis attack peanuts simultaneously and cause different types of damage. In this study, we compared the life histories and larval morphologies through field investigations and scanning electron microscopy (SEM) observations. These cross-instar white grubs are similar in sizes, but exhibit morphological differences on their mouthparts, thoracic legs, anal slits, and rasters. This study presents a novel approach to larval identification, with a goal of generating new insights into integrated pest control practices on white grubs.

Insights into ribosomal DNA dominance and magnification through characterization of isogenic deletion alleles.

The major loci for the large primary ribosomal RNA (rRNA) genes (35S rRNAs) exist as hundreds to thousands of tandem repeats in all organisms and dozens to hundreds in Drosophila. The highly repetitive nature of the ribosomal DNA (rDNA) makes it intrinsically unstable, and many conditions arise from the reduction in or magnification of copy number, but the conditions under which it does so remain unknown. By targeted DNA damage to the rDNA of the Y chromosome, we created and investigated a series of rDNA alleles. We found that complete loss of rDNA leads to lethality after the completion of embryogenesis, blocking larval molting and metamorphosis. We find that the resident retrotransposons-R1 and R2-are regulated by active rDNA such that reduction in copy number derepresses these elements. Their expression is highest during the early first instar, when loss of rDNA is lethal. Regulation of R1 and R2 may be related to their structural arrangement within the rDNA, as we find they are clustered in the flanks of the nucleolus organizing region (NOR; the cytological appearance of the rDNA). We assessed the complex nucleolar dominance relationship between X- and Y-linked rDNA using a histone H3.3-GFP reporter construct and incorporation at the NOR and found that dominance is controlled by rDNA copy number as at high multiplicity the Y-linked array is dominant, but at low multiplicity the X-linked array becomes derepressed. Finally, we found that multiple conditions that disrupt nucleolar dominance lead to increased rDNA magnification, suggesting that the phenomena of dominance and magnification are related, and a single mechanism may underlie and unify these two longstanding observations in Drosophila.

Evaluation of insecticide residues against spotted lanternfly (Hemiptera: Fulgoridae).

Lycorma delicatula White (Hemiptera: Fulgoridae), spotted lanternfly, is a univoltine, phloem-feeding, polyphagous and invasive insect in the United States. Although a primary host for this species is Ailanthus altissima (Mill.) Swingle, tree of heaven, L. delicatula also feeds on many other plant species, including cultivated grapevines. As this species continues to spread, it is important to develop effective management tools. Here, we evaluated the residual efficacy of 4 insecticides commonly used in tree fruit management programs: dinotefuran, bifenthrin, carbaryl, and thiamethoxam. First, all mobile life stages (early instars, late instars, and adults) of L. delicatula were exposed for 1 h to dry insecticide residues (18 h old) applied to glass or A. altissima bark surfaces. While some mortality was detected immediately following the 1 h exposure period, 100% mortality occurred within 24 h for all materials and life stages exposed on both glass and bark surfaces. To evaluate longer residual activity of these materials, groups of adult L. delicatula were introduced into cages containing A. altissima trees treated with the same individual insecticides and exposed 6 h to residues that were 18 h or 7 days old. Paired, untreated A. altissima served as controls. In these bioassays, 48 h mortality for 18 h old residue reached 95% for thiamethoxam and 100% for bifenthrin and dinotefuran. Seven-day-old bifenthrin and dinotefuran residues again yielded 100% mortality, while thiamethoxam resulted in 58% mortality, and carbaryl yielded only 13.3% and was not significantly different from the control. These results clearly document the efficacy of specific insecticide applications as management tools against L. delicatula.

Pathogens of the oak processionary moth Thaumetopoea processionea: Developing a user-friendly bioassay system and metagenome analyses for microorganisms

The oak processionary moth (OPM) Thaumetopoea processionea is a pest of oak trees and poses health risks to humans due to the urticating setae of later instar larvae. For this reason, it is difficult to rear OPM under laboratory conditions, carry out bioassays or examine larvae for pathogens. Biological control targets the early larval instars and is based primarily on commercial preparations of Bacillus thuringiensis ssp. kurstaki (Btk). To test the entomopathogenic potential of other spore-forming bacteria, a user-friendly bioassay system was developed that (i) applies bacterial spore suspensions by oak bud dipping, (ii) targets first instar larvae through feeding exposure and (iii) takes into account their group-feeding behavior. A negligible mortality in the untreated control proved the functionality of the newly established bioassay system. Whereas the commercial Btk HD-1 strain was used as a bioassay standard and confirmed as being highly efficient, a Bacillus wiedmannii strain was ineffective in killing OPM larvae. Larvae, which died during the infection experiment, were further subjected to Nanopore sequencing for a metagenomic approach for entomopathogen detection. It further corroborated that B.wiedmannii was not able to infect and establish in OPM, but identified potential insect pathogenic species from the genera Serratia and Pseudomonas.

An illustrated identification key to early instar larvae of forensically important Muscidae (Diptera) of the western Palaearctic region

There is a significant gap in the availability of comprehensive identification keys for the early larval stages of forensically important fly species. While well-documented identification keys exist for the third instar larvae, particularly for the Calliphoridae, Muscidae and Sarcophagidae families, there is a notable scarcity of keys for the first, except Calliphoridae, and the second instar larvae, with no such resources available for muscid species. The second instar larvae suffer the most from the lack of morphological descriptions and available identification keys. The Muscidae is one of the most frequently reported dipteran families of forensic importance colonising animal cadavers and human corpses. Nevertheless, descriptions of the morphology of their early instars remain scarce and limited to only a few species, thus their larval identification is challenging or impossible. Considering the numerous challenges associated with studying small-sized entomological material, we tested whether it is feasible to identify muscid flies to the species or at least genus level based predominantly on the details of the cephaloskeleton. To overcome the obstacle of observing details of small sclerites, especially their shapes and interconnections, we effectively employed confocal laser scanning microscopy (CLSM) as a supplementary method for light microscopy (LM). This study provides an identification key for first and second instar larvae of forensically important muscid species from the western Palaearctic (Europe, North Africa, Middle East). The proposed key primarily utilises details of the cephaloskeleton with only addition of external morphology.

Spinneret spinning field ontogeny and life history observations in the spider Palpimanus uncatus (Araneae: Palpimanidae).

As in other Palpimanidae, two pairs of posterior spinnerets present in typical Araneomorphae are vestigial in Palpimanus uncatus Kulczyński, 1909, with only the anterior lateral spinneret (ALS) pair prominent. Nevertheless, in late juvenile and adult females, spigots appear in the ancestral posterior spinneret region (PS). Consistent with these spigots serving cylindrical silk glands, females construct substantial egg sacs. While juveniles and adults exhibit a compressed PS, in postembryos it is fully extended. Piriform silk gland (PI) spigots form a linear array on ALSs from the 1st stadium, increasing in number during ontogeny by addition of PIs of the tartipore-accommodated (T-A) subtype (i.e., functional during proecdyses). The number of T-A PIs added from one stadium to the next and locations occupied by their spigots often exhibit a stereotypic pattern, especially consistent in early instars. The number of non-T-A PIs remains constant through ontogeny from the 1st stadium: one per ALS rather than the two per ALS inferred in a few araneoids. The secondary major ampullate silk gland (2° MaA) spigot, primitively uni-shafted among araneomorphs, has become modified into a multi-shafted spigot with extended base, the number of shafts increasing during ontogeny. However, the multiple ducts that connect to the shafts continue to be accommodated during proecdysis by a single enormous tartipore. Sexual dimorphism is present, with late stadium females having greater numbers of T-A PI spigots and 2° MaA spigot shafts. Observations are presented pertaining to feeding behavior, sexual cannibalism (absent), habitat, winter diapause, numbers of molts, and longevity.

Larval mosquito predation: evaluation of the effectiveness of five aquatic arthropod species against larvae of Culex pipiens Linnaeus, 1758 (Diptera: Culicidae)

ABSTRACT Mosquitoes are insects of medical interest. They contribute to the transmission and spread of many viral and parasitic diseases. Various methods have been used to control mosquitoes such as conventional insecticides, which are widely used throughout the world and have a negative impact on the environment and targeted species. Predatory insects are significant for the biocontrol of various pests, including the important potential against the larval instars of mosquitoes. In this study, we tested the efficacy of five species Piona uncata Koenike, 1888; Notonecta glauca Linnaeus, 1758; Corixa punctata Illiger, 1807, Ilyocoris cimicoide Linnaeus, 1758; and Sympetrum striolatum Charpentier, 1840 against the fourth instars larvae of Culex pipiens Linnaeus, 1758, according to two exposure phases (Light phase, Twilight phase). The predation assays show a significant effect of tested species against mosquito larvae with the following decreasing order of efficacy: S. striolatum> N. gluca> P. uncata> I. cimicoides> C. pinctata. The early larval instars are the most favourable trophic choice of the five predatory species. On the other hand, we noticed a difference in the predation rate for each species during the two experimental periods. The light phase exhibits the highest predatory efficacy than the twilight phase.

Impact of Aphis pomi-tending Formica rufa (Hymenoptera: Formicidae) on biological parameters of Hippodamia variegata (Coleoptera: Coccinellidae).

One of the key reasons for the poor performance of natural enemies of honeydew-producing insect pests is mutualism between ants and some aphid species. The findings demonstrated that red wood ant, Formica rufa Linnaeus (Hymenoptera: Formicidae) had a deleterious impact on different biological parameters of the lady beetle, Hippodamia variegata Goeze (Coleoptera: Coccinellidae). H. variegata laid far fewer eggs in ant-tended aphid colonies, laying nearly 2.5 times more eggs in ant absence. Ants antennated and bit the lady beetle eggs, resulting in significantly low egg hatching of 66 per cent over 85 per cent in ant absent treatments. The presence of ants significantly reduced the development of all larval instars. The highest reduction was found in the fourth larval instar (31.33% reduction), and the lowest in the first larval instar (20% reduction). Later larval instars were more aggressively attacked by ants than earlier instars. The first and second larval instars stopped their feeding and movement in response to ant aggression. The third and fourth larval instars modified their mobility, resulting in increased ant aggression towards them. Adult lady beetles were shown to be more vulnerable to ant attacks than larvae. However, H. variegata adults demonstrated counterattacks in the form of diverse defensive reaction behaviours in response to F. rufa aggression.

Report of <i>Maruca vitrata</i> (F) Nucleopolyhedrovirus

This study explores the potential of nucleopolyhedroviruses (NPVs) as a sustainable solution for managing legume pod borer Maruca vitrata (F). Distinctive signs of viral infection, such as suspended deceased larvae on cowpea leaves, and virus spread have been observed. Microscopic examination reveals characteristic polyhedral inclusion bodies (PIBs), confirming MaviNPV as the causative agent. Symptoms, including decreased activity and mortality in younger larvae, larval-pupal intermediates and deformed pupae have been observed. Reproductive disruption is evident through the absence of an egg mass and discharge of fluid from emerged adults. Bioassay results highlight age-dependent susceptibility, with higher mortality in early instars.

Insecticide resistance level of Aedes aegypti L. (Diptera: Culicidae) in northern Mexico

Objective: To determine the response of the larvae of three Ae. aegypti populations from the Mexican North Pacific region to insecticides with different mode of action.
 Design/Methodology/Approach: Three colonies were obtained placing ovitramps in peridomestic sites in Guadalajara (Jalisco), Culiacan (Sinaloa), and La Paz (Baja California Sur). Based on the methodology proposed by WHO, the bioassays were carried out with F1 larvae in the early fourth instar.
 Results: The larvae from the three field colonies had high resistance to permethrin and low resistance to deltamethrin; however, they were susceptible to Spinosad and Bacillus thuringiensis var. Israelensis. The Culiacan strain showed a high resistance to the malathion and propoxur insecticides.
 Study Limitations/Implications: The results provided valuable information about the response of these populations to insecticides, which are useful to establish resistance in the lab. Consequently, further studies should be carried out to complement the information obtained in these field tests.
 Findings/Conclusions: The data indicated resistance levels to pyrethroid insecticides (mainly permethrin), as well as to organophosphates and carbamates.