Leaf scarring by the weevils Neochetina eichhorniae and N. bruchi enhances infection by the fungus Cercospora piaropi on waterhyacinth, Eichhornia crassipes

Additive or synergistic effects among introduced and native insect and plant pathogen agents are necessary to achieve biological control of waterhyacinth (Eichhornia crassipes), a globally damaging aquatic weed. In field plots, plants were infested with waterhyacinth weevils (Neoechetina bruchi and N. eichhorniae) and leaves were scarred by weevil feeding. Subsequent infection by the fungal pathogen Cercospora piaropi caused necrotic lesions to form on leaves. Necrosis development was 7.5- and 10.5-fold greater in plots augmented with both weevils and C. piaropi and weevils alone, respectively, than in plots receiving only C. piaropi. Twenty-four days after weevil infestation, the percentage of laminar area covered by lesions on third-youngest and oldest live leaves was elevated 2.3–2.5-fold in plots augmented with weevils. Scar density and necrosis coverage on young leaf laminae were positively correlated, even though antipathogenic soluble peroxidases were elevated 3-fold in plots augmented with weevils alone or weevils and C. piaropi. Combined weevil and fungal augmentation decreased shoot densities and leaves per plant. In a no-choice bioassay, weevil feeding on oldest but not young leaves was reduced 44 two weeks after C. piaropi inoculation. Protein content and peroxidase activities were elevated 2–6-fold in oldest leaves three weeks after inoculation. Augmentation with both waterhyacinth weevils and C. piaropi led to the development of an additive biological control impact, mediated by one or more direct interactions between these agents, and not plant quality effects.     

Integration of Biological Control and Native Seeding to Restore Invaded Plant Communities

Disturbed natural areas frequently experience invasion by introduced plant species that can reduce native biodiversity. Biological control can suppress these introduced species, but without restoration another introduced species can invade. Integration of biological control with concurrent revegetation can both aid in weed reduction via interspecific plant competition and establish a restored native plant community. This 3‐year study investigated an integrated approach to controlling the introduced annual Mile‐a‐minute weed (Persicaria perfoliata [L.] H. Gross [Polygonaceae]) using the biocontrol weevil Rhinoncomimus latipes Korotyaev (Coleoptera: Curculionidae) and restoration planting using a native seed mix. A fully factorial design tested weevils and seeding, separately and together, using insecticide to eliminate weevils. The weevils together with the native seed mix reduced P. perfoliata percent cover in 2009 and 2010, and peak seed cluster production in 2010, compared to the insecticide ? no seed control treatment. Persicaria perfoliata final dry biomass was reduced by 75% in 2010 and by 57% in 2011 in the weevils plus seed treatment compared to the control, with weevils having the greatest effect in 2010 and the seed treatment having the greatest impact in 2011. Results suggest an additive effect of biocontrol and seeding in suppressing P. perfoliata. Seeded treatments also developed the highest native plant species richness and diversity, comprised of spontaneous recolonization in addition to species from the seed mix. Results support the use of integrated management of this invasive weed, with suppression through biological control and native revegetation together helping prevent reinvasion while restoring native plant biodiversity.     

Field host-specificity of the mile-a-minute weevil,Rhinoncomimus latipes Korotyaev (Coleoptera: Curculionidae)

The safe practice of biological control relies, in part, on an accurate evaluation of a potential agent’s host-specificity via testing through a “filter of safety”. The results of laboratory tests may differ from those obtained in open field host-specificity tests, where agents are able to use their full range of host-selection behaviors. It was hypothesized that Rhinoncomimus latipes (Coleoptera: Curculionidae), the biological control agent released against mile-a-minute weed, Persicaria perfoliata (Polygonaceae), would not feed or oviposit on nontarget plants in a two-phase, open field setting. Ten weevils were placed at the base of each of 13 test plant species in a randomized complete block design with six replicates. Weevils placed at the base of mile-a-minute weed were marked with yellow fluorescent dust, and yellow weevils were subsequently found only on mile-a-minute. Weevils placed at the base of nontarget plants (marked with red fluorescent dust) rapidly colonized mile-a-minute weed. Three hours after release, the number of R. latipes found on mile-a-minute weed was significantly higher than predicted by a random distribution of weevils on all test plants. The likelihood of finding more weevils on mile-a-minute compared to nontarget plant species was 31.0% at 3 h and increased to 96.5% at 44 h after release. Whereas prerelease studies showed feeding at low levels on 9 of the 13 plant species tested here, under open field conditions R. latipes did not feed on any nontarget plant species and dispersed from these plants. In an open field setting, where the weevil was able to use its full range of host-selection behaviors, there was no observed risk of nontarget effects for any species tested.     

Host range of Ceutorhynchus assimilis (Coleoptera: Curculionidae), a candidate for biological control of Lepidium draba (Brassicaceae) in the USA

Ceutorhynchus assimilis has been selected as a potential biological control agent of Lepidium draba, which is a Eurasian invasive weed in North America. Preliminary studies indicated specificity of this weevil collected in southern France on L. draba. This result was in discord with the pest status of C. assimilis found in the literature. Host-specificity tests based both on field and laboratory experiments showed heterogeneity in the host spectrum of the weevils reared from different host-plants as determined by larval development. However, no distinguishable morphological differences could be visually detected between the populations feeding on different host-plants. All sampled populations of weevils were polyphagous as adults. Weevils reared from L. draba were specific to this plant for their complete larval development. Conversely, populations living on other wild and cultivated Brassicaceae species were not able to use L. draba as a host plant. Such differentiation is further highlighted by other biological aspects such as plant infestation rates, sex-ratio, duration of larval development, and differences in the timing of their life cycles. These results demonstrate that C. assimilis, an insect species formerly considered as a pest of Brassicaceae, is characterized by its host-range variability, with one population being potentially useful in the biological control of L. draba. Moreover, this example points to the need to test multiple populations of biological control agents in assessing risk.     

Biological control of water hyacinth in California’s Sacramento–San Joaquin River Delta: observations on establishment and spread

Water hyacinth (Eichhornia crassipes (Martius) Solms-Laubach) is a serious invasive weed in the Sacramento–San Joaquin River Delta of California. Three insects: Neochetina eichhorniae Warner and Neochetina bruchi Hustache (Coleoptera: Curculionidae) and Niphograpta (=Sameodes) albiguttalis (Warren) (Lepidoptera: Crambidae) were released during 1982–1987 at four locations for the biological control of water hyacinth. Observations in 1985 suggested that all three species had established. By 2002, water hyacinth populations in the Delta still required an aggressive chemical control campaign and the status of the biological control agents was in question. In late 2002, a field survey to determine the distribution and abundance of the released insects was performed. Water hyacinth plants were collected by boat in the main water channels and from land at smaller sloughs and examined for insects. In total, 27 sites with water hyacinth distributed across the Delta were examined of which 21 had weevils. Weevil abundance ranged from 0 to 10.9 weevils per plant, with an average of 0.93 (±0.47 SEM) adult weevils per plant. All weevils (n?=?518) were identified as N. bruchi. No N. eichhorniae were recovered and no larvae or evidence of larval feeding by N. albiguttalis were observed. A total of 322 weevils were examined for microsporidia and none was found infected, indicating an infection rate of less than 1%. These results suggest that N. bruchi may be the only established biological control agent of water hyacinth in the Delta and that infection by microsporidia does not appear to be limiting its population abundance.     

Field assessment of a frond-feeding weevil, a successful biological control agent of red waterfern, Azolla filiculoides, in southern Africa

Azolla filiculoides (red waterfern) is a small, floating fern native to South America, that has invaded aquatic habitats, predominantly water resevoirs in southern Africa. A frond-feeding weevil, Stenopelmus rufinasus Gyllenhal (Coleoptera: Curculionidae), was imported from Florida, USA, and released as a biological control agent against this weed in South Africa at the end of 1997. To date, 24,700 weevils have been released, which has resulted in local extinction of red waterfern at 81% of the 112 release sites. The weevil has not failed to control a single site. Several sites were, however, lost due to flooding or drainage of dams. The surface area of weed controlled totalled 203.5 ha. On average, A. filiculoides was controlled in infested sites in 6.9 (±4.3) months. The weed recolonized at 22 of the sites (through either spore germination or dispersal by waterfowl), but the weevils subsequently spread to all of these sites and successfully caused local extinction of the weed at 18 of the sites. Five years after the release of the weevil, the weed no longer poses a threat to aquatic systems in southern Africa. In comparison to other biological control programs of aquatic weeds, the program against A. filiculoides in southern Africa ranks among the most successful cases anywhere in the world.     

Observations on the effect of the weevils Neochetina eichhorniae Warner and Neochetina bruchi Hustache on the growth of water hyacinth

Water hyacinth Eichhornia crassipes (Mart.) Solms. is an aquatic weed that infests most of the White Nile system in the Sudan. Serious economical and ecological problems are caused by this weed. The two weevils Neochetina eichhorniae and Neochetina bruchi were imported and released in an attempted biological control against the weed. The adults of these weevils attack the plant and feed by removing tissues from the leaf pseudolamina and petioles. The larvae tunnel inside the petioles and the crown. The optimum temperature for feeding and development of both species is 25° C. Results obtained from stocking hyacinth plants with adults and larvae of both species separately revealed that N. bruchi is more efficient in checking the growth of the plant. The progeny of a pair of N. bruchi and N. eichhorniae reared separately on 41 hyacinth plants for a period of 61 days (one generation period) reduced their population growth by 25.4% and 12.7% respectively. The progeny of both species in a mixed culture reduced the growth of the plants by 22.5% in the same period, while in the control the population of the plants increased 136.6%.     

Pre-release impact assessment of two stem-boring weevils proposed as biological control agents for Alliaria petiolata

Experimental studies can be useful tools to test plant responses to herbivory and to quantify the impact of potential biological control agents prior to their release. We evaluated the per-capita effect of Ceutorhynchus alliariae and C. roberti, two stem-boring weevils currently being investigated as potential biological control agents for garlic mustard, Alliaria petiolata, in North America. Weevils were released at three different densities in individual and mixed-species treatments onto potted plants of A. petiolata. Damage by C. roberti alone and by both weevils combined caused an increase in the numbers of inflorescences produced per plant. Although plants could compensate for low levels of damage, moderate to high levels of damage by both C. alliariae and C. roberti, individually and in combination, caused a decrease in plant height and a reduction in seed output per plant. The damage inflicted by both weevil species is similar so the overall impact of both species combined can be predicted by summing the impact of each species alone. Provided they are sufficiently host specific, both weevils could be released as biocontrol agents. Because reduced seed production is necessary to suppress A. petiolata populations, both species have the potential to contribute to control of A. petiolata in North America.     

Impact of herbivory on mile-a-minute weed (Persicaria perfoliata) seed production and viability

The monophagous weevil Rhinoncomimus latipes Korotyaev (Coleoptera: Curculionidae) has been introduced into North America as a biological control agent for the invasive vine mile-a-minute weed, Persicaria perfoliata (L.) H. Gross. This weevil has been shown to reduce the percent cover of mile-a-minute and the number of seed clusters produced, as well as altering the phenology of seed production. However, prior work has not examined the potential impact of the weevil on seed viability and numbers of seeds per cluster. When both adult and larval weevils fed on whole plants in the greenhouse, seed production and fruit maturation were delayed and both the total number of seeds and number of seeds per cluster were reduced. Overall, weevils in greenhouse cages reduced the reproductive potential of P. perfoliata by 35%. When adult weevils were confined on developing seed clusters in the field, the number of seeds produced per cluster, the weight of seeds produced, and seed viability all decreased. Overall, the number of viable seeds per cluster was reduced by 37% in the presence of adult weevils. Taken together, these findings demonstrate that this biological control agent can have important impacts on the reproductive potential of its target weed through mechanisms that have not previously been shown.     

Host utilization of field-caged native and introduced thistle species by Rhinocyllus conicus

Rhinocyllus conicus Fr?elich was introduced from Europe into North America as a biological control agent of the exotic weed Carduus nutans L. Concern exists over the feeding of this weevil on at least 25 species of native Cirsium thistles. Beginning in 2008, cage studies isolating adults of R. conicus on buds and flower heads of all eight thistle species (native and introduced) recorded from Tennessee were conducted to test if R. conicus could use these species for reproduction and what impacts larval feeding of R. conicus may have on seed production. Larvae of R. conicus completed development in heads of the native species C. carolinianum (Walter) Fernald and Schubert. and C. horridulum Michaux, and significant reductions in seed numbers of both species occurred during 2008. Rhinocyllus conicus oviposited on both C. carolinianum and C. horridulum at significantly greater levels than the introduced species C. arvense (L.) Scopoli and C. vulgare (Savi) Tenore. Infested heads of C. carolinianum contained numbers of R. conicus per centimeter of plant head width similar to Ca. nutans in 2008, and both native species contained numbers of R. conicus per centimeter of plant head width similar to C. arvense and C. vulgare in 2009. Body length was similar between R. conicus reared on native thistles and its target host Ca. nutans. This report is the first documentation of R. conicus feeding and reproducing on C. carolinianum and C. horridulum. Although R. conicus has been observed only on introduced thistles in naturally occurring populations in this region, the utilization of C. carolinianum and C. horridulum as host species in controlled conditions warrants continued monitoring of field populations and further investigation into factors that may influence nontarget feeding in the future.     

Biological control of Salvinia molesta in some areas of Moremi Game Reserve,Botswana

The Curculionid weevil, Cyrtobagous salviniae Calder & Sands, has been established on Salvinia molesta (salvinia) in Botswana. The study determined the intensity of weevil activity on the weed at the margin and the centre of four selected sites on the Khwai system of the Okavango Delta. Random samples of salvinia were collected from each site at monthly intervals in 1998 to extract weevils and to demonstrate the effect of weevil on the weed. The rate at which the weed was controlled at different sites varied with mat and weevil density. The biological control at Paradise Pools was moderate without much increase in the weed biomass per m², while fluctuations in both weevil and plant populations were noticed in the Khwai streams. Weevil numbers remained low at Dombo for the first nine months of the year, during which time the mat density increased. With the onset of higher temperatures, weevil numbers increased to 155 and 457/kg fresh weight of salvinia at the margin and centre respectively in Dombo Pool in early summer. A significant control in MGR 6 HATAB pool between mat biomass and the weevil number resulted in the disappearance of the weed in three months. This study shows that C. salviniae is an effective biological control agent of S. molesta in semiarid areas.     

Complementing biological control with plant suppression: Implications for improved management of parthenium weed (Parthenium hysterophorus L.)

Parthenium hysterophorus L. is a weed of global significance that has become a major weed in Australia and many other parts of the world. A combined approach for the management of parthenium weed using biological control and plant suppression, was tested under field conditions over a two-year period in southern central Queensland. The six suppressive plant species, selected for their demonstrably suppressive ability in earlier glasshouse studies, worked synergistically with the biological control agents (Epiblema strenuana Walker, Zygogramma bicolorata Pallister, Listronotus setosipennis Hustache and Puccinia abrupta var. partheniicola) present in the field to reduce the growth (above ground biomass) of parthenium weed, by between 60–86% and 47–91%, in Years 1 and 2, respectively. The biomass of the suppressive plants was between 6% and 23% greater when biological control agents were present than when the biological control agents had been excluded. This shows that parthenium weed can be more effectively managed by combining the current biological control management strategy with selected sown suppressive plant species, both in Australia and elsewhere.     

Melding ecology,classical weed biocontrol,and plant microbial ecology can inform improved practices in controlling invasive plant species

Early research leading to the successful biological control of invasive species such as Opuntia spp., and Hypericum perforatum set examples and provided data useful for research programs that would follow. However, this early work failed to become established as a source of applicable principles for later workers in weed biocontrol. Recently, retrospective and parallel studies have been suggested as a means to reengage with earlier work to derive useful ideas and data to enhance future programs in weed biocontrol. Parallel studies by workers in plant community ecology on the nature of feedback elicited by plant species in their invaded and native range have shown the importance of soil microbial communities in effecting feedback. Retrospective reexamination of previous studies would likely provide clues to other insect–plant pathogen interactions in addition to those described by the author and others. The effects of invasive species in profoundly altering soil microbial communities point to the need for further studies on key microbial species contributing to or driving the impact of biocontrol. These collective data suggest that the desired goal of selecting for and utilizing stronger biocontrol agents to reduce nontarget effects and to increase the impact of biological control programs would be best served by prerelease studies that assess the propensity of a candidate agent for direct or indirect interaction with other agents. This could be assessed through the use of survival analysis. Overall, parallel empirical and retrospective studies should be a necessary part of how biological control is practiced.     

Impact of the biological control agent Rhinoncomimus latipes (Coleoptera: Curculionidae) on mile-a-minute weed,Persicaria perfoliata,in field cages

A host-specific Asian weevil, Rhinoncomimus latipes Korotyaev, was approved in 2004 for release in North America for control of mile-a-minute weed, Persicaria perfoliata (L.) H. Gross (formerly Polygonum perfoliatum L.), an invasive annual vine from Asia. The impact of R. latipes feeding on P. perfoliata was studied in field cages over a 2-year period. In 2006, 20 weevils introduced into cages with single plants in May (when weevils first emerge from overwintering) suppressed seed production for about 9 weeks, while weevils introduced in June (when the first summer generation of adults emerge) did not affect seed phenology. Plants in all cages produced substantial numbers of seeds late in the year, but the average seed (achene) weight was reduced for plants with 20 weevils per plant introduced in May. In 2007, plants grown with some competition from other plants within field cages showed substantial mortality, with 63% of plants with 10 or 20 weevils and 75% of plants with 40 weevils per plant dead by mid-August, compared with 12.5% of control plants. Reproduction was delayed by more than a month in surviving plants with 10 or 20 weevils, and by more than 2 months in the few survivors with 40 weevils. Surviving plants with 40 weevils per plant showed loss of apical dominance, which can allow plants to compensate for herbivore damage, but in the case of a light-adapted vine like P. perfoliata may prevent the plants from achieving needed sun exposure. These results suggest that R. latipes feeding on P. perfoliata has the potential to impact plant growth and reproduction, and can put affected plants at a substantial competitive disadvantage.     

Melding ecology, classical weed biocontrol, and plant microbial ecology can inform improved practices in controlling invasive plant species

Early research leading to the successful biological control of invasive species such as Opuntia spp., and Hypericum perforatum set examples and provided data useful for research programs that would follow. However, this early work failed to become established as a source of applicable principles for later workers in weed biocontrol. Recently, retrospective and parallel studies have been suggested as a means to reengage with earlier work to derive useful ideas and data to enhance future programs in weed biocontrol. Parallel studies by workers in plant community ecology on the nature of feedback elicited by plant species in their invaded and native range have shown the importance of soil microbial communities in effecting feedback. Retrospective reexamination of previous studies would likely provide clues to other insect–plant pathogen interactions in addition to those described by the author and others. The effects of invasive species in profoundly altering soil microbial communities point to the need for further studies on key microbial species contributing to or driving the impact of biocontrol. These collective data suggest that the desired goal of selecting for and utilizing stronger biocontrol agents to reduce nontarget effects and to increase the impact of biological control programs would be best served by prerelease studies that assess the propensity of a candidate agent for direct or indirect interaction with other agents. This could be assessed through the use of survival analysis. Overall, parallel empirical and retrospective studies should be a necessary part of how biological control is practiced.     

Effects of Rhinoncomimus latipes on the growth and reproduction of Persicaria perfoliata,an invasive plant in North America

Native to Asia, mile-a-minute Persicaria perfoliata, is an invasive weed in North America, and the weevil Rhinoncomimus latipes is a host-specific insect agent which occurs widely in China. We conducted a common garden experiment to compare P. perfoliata plant responses of native and invasive populations to herbivory by the weevils from different origins. We found weevils from Hunan, Hubei and Heilongjiang Provinces had strong, moderate and weak ability to suppress host plant, respectively. Weevils from Hunan and Hubei Provinces had stronger impact on the growth of both native and invasive plant populations than the weevil from Heilongjiang Province. The losses in seed output of invasive plants were also significantly greater than natives in the weevil treatments. Our results suggested that the weevil population from Hunan Province may be the most suitable for the control of mile-a-minute, while the population from Heilongjiang Province may be the least suitable due to climate matching.     

Winter mortality of Aceria chondrillae, a biological control agent released to control rush skeletonweed (Chondrilla juncea) in the western United States

Abstract:  Classical biological control of weeds is based on the assumptions that: (1) plant species are in part invasive in their introduced range because of the absence of coevolved specialist herbivore arthropods and plant pathogens; and (2) that these specialist herbivores can regulate host-plant populations. Although the need for quantitative post-release monitoring studies testing these assumptions has been acknowledged repeatedly, the number of assessments is still remarkably small and usually restricted to systems with notable impact of an agent species. However, studying systems where biological control agents cause no observable target weed reductions may be important to identifying factors that limit the population size or impact of biological control agents. Three biological agents were released for the control of the herbaceous perennial rush skeletonweed, Chondrilla juncea in North America between 1975 and 1977. Although all three species are widely established, weed densities are increasing and there is little quantitative information on factors limiting biological control efficacy. We examined the winter biology and survivorship of the rush skeletonweed gall mite Aceria chondrillae at two rush skeletonweed field sites in south-western Idaho over 2 years. Gall mite winter mortality was high (>90%) in both years and for both sites. Gall mites were more abundant on plants that produced rosettes in fall and rush skeletonweed plants growing on southern aspect were 3.4 times more likely to produce rosettes than those growing on northern aspects. Our data suggest that A. chondrillae population densities are limited by its high winter mortality. The gall mites may require fall rosettes to successfully survive the winter, which are commonly absent on north-facing aspects, impairing the efficacy of A. chondrillae to control rush skeletonweed in the intermountain western United States.     

Pre-release evaluation of the efficacy of the leaf-sucking bug Carvalhotingis visenda (Heteroptera: Tingidae) as a biological control agent for cat's claw creeper Macfadyena unguis-cati (Bignoniaceae)

In classical weed biological control, assessing weed response to simulated herbivory is one option to assist in the prioritization of available agents and prediction of their potential efficacy. Previously reported simulated herbivory studies suggested that a specialist herbivore in the leaf-feeding guild is desirable as an effective biological control agent for cat's claw creeper Macfadyena unguis-cati (Bignoniaceae), an environmental weed that is currently a target for biological control. In this study, we tested (i) whether the results from glasshouse-based simulated herbivory can be used to prioritise potential biological control agents by evaluating the impact of a leaf-sucking tingid bug Carvalhotingis visenda (Drake & Hambleton) (Hemiptera: Tingidae) in quarantine; and (ii) the likely effectiveness of low- and high-densities of the leaf-sucking tingid after its release in the field. The results suggest that a single generation of C. visenda has the potential to reduce leaf chlorophyll content significantly, resulting in reduced plant height and leaf biomass. However, the impact of one generation of tingid herbivory on below-ground plant components, including the roots and tuber size and biomass, were not significant. These findings are consistent with results obtained from a simulated herbivory trial, highlighting the potential role of simulated herbivory studies in agent prioritisation.     

Spatial prediction of habitat overlap of introduced and native thistles to identify potential areas of nontarget activity of biological control agents

Nontarget feeding of Rhinocyllus conicus Fr?elich and Trichosirocalus horridus (Panzer) on native North American thistles in the genus Cirsium has been documented. Some species of these native thistles have shown greater infestation levels of R. conicus in populations that are in close proximity to the target plant species, Carduus nutans L. In 2005 a study was initiated to identify areas of potential nontarget feeding by R. conicus and T. horridus on thistle species by predicting habitats of two known introduced hosts [C. nutans and Cirsium vulgare (Savi) Tenore] and two native species [Cirsium carolinianum (Walter) Fernald and Schubert and C. discolor (Muhlenberg ex Willdenow) Sprengel] using Mahalanobis distance (D(2)). Cumulative frequency graphs showed that the D(2) models for all four plant species effectively identified site conditions that contribute to the presence of the respective species. Poisson regression showed an association between D(2) values and plant counts at field-test sites for C. nutans and C. carolinianum. However, negative binomial regression detected no association between D(2) values and plant counts for C. discolor or C. vulgare. Chi-square analysis indicated associations between both weevil species and sites where C. vulgare and Carduus nutans were found, but not between the weevil and native thistle species. Habitats of C. nutans and Cirsium carolinianum overlapped in ≈12% of the study area. Data-based habitat models may provide a powerful tool for land managers and scientists to monitor native plant populations for nontarget feeding by introduced biological control agents.     

Development and Degeneration of Flight Muscles in Neochetina eichhorniae (Coleoptera; Curculionidae), Potential Biocontrol Agent of the Aquatic Weed, Eichorniae crassipes

The water hyacinth weevil, Neochetina eichhorniae, is an effective biological control agent of the aquatic weed Eichorniae crassipes. The adults under field conditions have degenerated indirect flight muscles that explains their inability to fly. A study on the factors initiating flight muscle development in adults was carried out. Among the various abiotic factors studied, density of weevils per plant and high temperature in presence of food initiated and accelerated flight muscle development. Absence of food did not influence muscle development. No inter-relationship between flight muscle development and degeneration could be observed.