Swallowtails workshop, Part 2: Paper 7. Avoiding parasitoids and disease part 2. Nigel Venters: July 2012

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2 Avoiding parasitoids and disease part 2. : July Parasitoids. In the Swallowtail Workshop, Part1: Paper 7, I discussed how to protect your stock from parasitoid infection. This is accomplished by keeping your stock protected at all times by using very fine parasitoid-proof netting. In this paper I will expand on this and cover the different types of potential pests that you are likely to encounter in your breeding programme. Although good parasitoid-proof netting will keep you safe from parasitoids, you may find it useful to learn a little more about each of the different parasitoid families and how they complete their life-cycles. Do remember that the adult butterflies are never attacked by parasitoids, only eggs, larvae and pupa are at risk. Chalcid Wasps No one knows just how many different species there are of Chalcid wasps. Although there are around 22,000 different species described, it is generally thought that the actual number is likely to be near 500,000 species! Most species infect insects in general and not just butterflies and moths. They often have a metallic blue or green body and are tiny! The smallest insect known to man is a Chalcid wasp, known as Dicopomorpha echmepterygis. Depending on species, they attack the egg, larva, and pupa stages. Hundreds of adults can emerge from a single pupa! Because they are so small, Chalcid wasps can be easily overlooked in your breeding operation. It is for this reason that I know I can never exclude them from my flight-house completely, so I use cages with complete protection for all preadult stages. Most Chalcid wasps that attack swallowtails target the pre-pupa, and wait until the skin is shed to lay their eggs while the pupal shell is still soft. The wasps cannot lay eggs until the larva sheds its skin to pupate, and often a wasp will find and sit on the back of a 5th instar larva waiting for several days until it becomes a pupa. It is actually quite easy just to pick the wasp off the back of the larva or pre-pupa as Page 1

3 a preventative method. If you find a wasp sitting on a fresh pupa you can be sure that it has already laid its eggs and the pupa will die, but if you remove the wasp before the larva sheds its skin it will be safe. The adult butterflies are safe from infection by any parasitoids. There is no effective way to eradicate these tiny wasps, except by giving complete protection to the vulnerable butterfly development stages. Detection, isolation and destruction of infected eggs, larvae and pupae are also important measures to control parasitoids. Protection means that they will have no opportunity of reproducing, and therefore, can never build up into devastating numbers. Detection is usually easy at pupal stage, the abdomen becomes distended and gradually the space between the abdominal segments changes from green to dark brown. Pupae showing these symptoms should be destroyed, either crushed or frozen to kill the parasitoids. However, if they do gain access to your stock, they can build to enormous numbers and wipe you out! So do take care! Ichneumon Wasps Ichneumon Wasps (often referred to as Ichneumon flies) and the closely related Braconid wasps all have a similar appearance, and are definitely Wasp-like. These can range in size from small to more than 2 centimeters in length. However, they are always larger than Chalcid wasps, and are easily spotted in your set-up. Due to their size, usually only a single adult will emerge from the infected larva or pupa. They are not known to attack eggs. The females of most species have a long ovipositor, that looks like a sting at their rear end. Many Ichneumon wasps have an extremely accurate sense of smell and they use this to detect their hosts. Ichneumon wasps are usually brightly-coloured, often with bright warning colours such as reds and yellows. They are in fact harmless to humans, and they merely use warning colours to deter their own predators from eating them. Page 2

4 Even when you have collected your pupae, unless you have protected your larvae these are still not safe. The larvae or pupae of Ichneumon wasps will often overwinter inside the butterflies and emerge in the spring to start their reproductive cycle all over again! Infected pupae usually show signs of discolouring before the wasp emerges from it; for example, a green pupa becomes duller, often with a yellowish tinge. You may wonder how a butterfly larva is not killed at an early stage by having such a large parasitoid eating it alive from the inside. Many parasitoids have a few tricks up their sleeve to overcome this problem. The first is that the parasitoid larva avoids eating any vital organs, and just eats the fat reserves being built up by the butterfly larva. More importantly, they employ the use of immune suppressants. This is in the form of releasing a special virus, which has co-developed with the parasitoids over millions of years. This virus enables the parasitoid larvae to remain undetected by its host. The parasitoid larvae can also release hormones that delay the butterfly s development, to allow them to complete their lifecycle and be ready to infect the next generation of butterfly larvae. The parasitoids are also affected by the hormones produced by the larva, so they know whether to overwinter or emerge in a few weeks. Sometimes the butterfly larva can fight back by suicidal behavior! An infected larva will often roam in the open, making it an easier prey for predators. Uninfected larvae take more care to hide themselves when they look for a pupation site. This is why so many larvae that you find easily are often infected and should be treated with a great deal of suspicion and always isolated from your healthy stock. There are some species of Ichneumon wasps that are not interested in infecting the actual butterfly larva, but attack it only to lay eggs in and on other existing parasites that the larvae have already been infected with. Unfortunately, the larvae still die! As with other parasitoids, there are a huge number of different species of Ichneumon wasps, and they, like the others have a world-wide distribution. Page 3

5 Tachinid flies. Tachinid flies are all similar in general appearance, and just look like a small common house fly. A general guide is to look for the bristles on their body, which are longer than you normally find on a house-fly. There are countless numbers of species, and there are many different ways in which the various species infect their hosts. Tachinid flies also have a world-wide distribution. Depending on species, Tachinid flies have many strategies for infecting their hosts. However, the majority of species (probably most) either lay their eggs directly on the skin of the larva, or inject their eggs using an extendable ovipositor. The eggs hatch rapidly, and are so well stuck on that it is virtually impossible to remove them without killing the larva! Some species lay a fully-formed hatching tiny larva on their host s skin, which immediately bores into the body. Another strategy is to lay eggs on the caterpillar host-plant. These are laid singly, and in these species a vast number of eggs are laid as wastage is, of course, high. (Tachinids often search for frass on the ground and then fly up to lay eggs in the trees above the frass that they find, so if you rear larvae in sleeves always make sure that you do not let the frass fall to the ground below when you clean out the sleeves.) Again, different species have different tactics. Some eggs hatch into tiny larvae and wait for their host to walk past them; they then immediately bore into their hosts skin. Other species remain as eggs for a long time, and wait for the larvae to ingest them as they eat the leaf. These are, of course, the most difficult species to prevent, especially if you are supplying cut host-plants for your larvae. Regardless of strategy, the result is the same, and the larva is eaten from the inside, as with other parasitoids, resulting in the death of the larva. Tachinid flies are a much larger species than most other parasitoids, so there is almost always only one parasitoid larva in each butterfly larva. Fortunately the normal precaution of using parasitoid-proof netting will defeat most Tachinid fly species. Luckily, larvae that are ingested, or are waiting on the host-plant ready to pounce on their victims, are fairly uncommon. However, it is always worth checking the frass at the bottom of the cages for the brown ovoid shaped pupae, which again Page 4

6 look just like a house-fly pupa. I occasionally find a Tachinid pupa when I am cleaning out a cage, and dispose of it. The vast majority of the larvae in the same cage will not be infected, so don t panic if you find one from time to time! Tachinid fly pupae are always formed externally from their hosts, and never pupate inside their hosts. Eggs are never attacked. Trichogramma Wasps. Trichogramma wasps are always tiny, and again are impossible to exclude from the flight-house. The problem is that, any parasitoid-proof netting fine enough to keep them out, would also impede the necessary air-flow in the flight-house. They only attack eggs, and have a wonderful sense of smell to detect them. A strange fact is that most individuals are females, and they do not need to pair to lay fertile eggs. This is known as parthenogentical or heterogamical reproduction. Trichogramma wasps are always tiny, and you just don t see them. They have a world-wide distribution, and in some regions account for mortality rates of 98% of eggs! I have found them to be more prevalent in tropical regions than in temperate areas; however, regardless of where you live, you are likely to be affected by these. Being so tiny, it does make you wonder how they can fly around and infect the eggs, but there are many strategies at play here! Apart from having an uncanny sense of smell, they will also hitch a ride on an adult butterfly, hop off when she lays an egg, and hop back on again as she moves off. The speed of egg-laying in these insects is impressive! She can determine immediately if the egg is healthy and will bypass any eggs previously infected by another wasp! The Trichogramma wasp s ability to produce fertile eggs without pairing (parthenogenesis) allows the species to explode in numbers in favourable conditions, as all offspring can lay eggs immediately they reach adulthood. Males are rare, and are only produced in times of stress to produce a genetic mix. One method of controlling egg parasitoids is to collect all the eggs that are laid each day and put them into separate labelled boxes, so you know which butterfly Page 5

7 the eggs came from and when they were laid. When all the larvae have hatched from the eggs (usually they will all hatch within a couple of days of each other) in a box just pop the box containing the remaining eggs in the freezer, as any parasitoids take longer to develop than larvae inside healthy eggs. This is of course time consuming, but the important objective is removal of all the infected eggs from your breeding environment which stops the next generation of wasps from continuing to infect your newly laid eggs. This shows a photo of a Trichogramma wasp holding on to a female butterfly s leg. It is hitching a ride so that it can infect each egg as it is laid. The speed of infecting each egg is amazing! This is particularly common in Swallowtails and other large butterfly species. One group, the Owl Butterflies (Caligo species) are particularly favoured, and up to 98% of the eggs that the butterfly lays may be infected in favourable conditions. General note on Parasitoids. Many parasitoids are species-specific, which means that they will only ever infect a single species. However, be aware that there are many other generalist species just waiting to get at your livestock! I hope that these notes have been interesting for you, but please don t panic. All of these parasitoids (apart from the occasional Tachinid fly!) can be completely avoided by using a parasitoid-proof netting over your stock. Before I move on to disease, I want to draw attention to another tiny pest that can cause mayhem in your operations. Hemiptera: the Bug family. This is a huge family, which include Aphids but also has many carnivorous species, the most famous are called Assassin bugs. Within this group are some tiny, opportunistic predatory bugs that will eat butterfly eggs and larger species that attack larvae. These bugs have a lethal hollow tube instead of jaws, which they insert into their prey to inject a poison to kill it. This also dissolves the internal organs, and the bugs then suck this soup out of the victim. Page 6

8 There are a number of species of these tiny insects world-wide, and they can devastate a cage if they get inside or are on the host-plant. Any suspicious empty eggs in a protected cage will indicate that some may be present. Check carefully using a magnifying glass, and remove them with an aspirator. A simple form of home made aspirator is shown below. This is a Pooter. A small lightweight solution for catching bugs quickly, and they end up in the canister. The one illustrated uses a clear plastic 35 mm film container (from the pre-digital photography era!) but any similar small sealable container will do. This works quite simply by sucking the mouth end of the tube and pointing the capture end at the bug, spider or whatever you want to remove from a cage. You will notice that the canister end of the sucking tube is covered by a small piece of netting. This prevents the bug coming into your mouth! You can collect many bugs, etc. in this, and their disposal is the simple process, of opening the canister and killing them. Diseases: bacterial, viral and fungal Although recognising disease may be obvious to experienced breeders, some new breeders may find the following information useful. Recognise Disease Infections Be aware, and recognise when your larvae are changing their skins! I have been contacted many times over the years by new breeders who have assumed that their larvae are diseased when they see them hunching up, their heads bowed over and not moving for a day or so, and then seeing a heaving motion under the skin! This is just the larva changing its skin, and it is important you do not disturb the larva at this stage. This is a normal process, and certainly not disease! Page 7

9 Also, just before pupation, the larva becomes restless and starts to wander about the cage looking for a suitable spot to pupate. The last dropping of a larva about to pupate always contains undigested host-plant and is sloppy, so do not worry if you see this happen. Only start to take action if you see the following symptoms: Diarrhoea. This is usually the first sign of infection; however, it can be caused because you have too much water in the host-plant (from standing it in water) Viral Infections. When infected with a virulent virus, the larva often collapses into a limp, elongated bag of skin, filled with black fluid and often, (but not always) hangs from its rear claspers. Others fall to the bottom of the cage. Either way, they often have black fluid dripping from the head. The skin ruptures easily, spreading the virus to other larvae very quickly. Sometimes, initially, the larvae take on a pale or even a granulated white powdery complexion. Viruses can remain in a latent form inside any stage of the butterfly s lifecycle. Infection is triggered when conditions favour the virus, and death is usually rapid. Important: Remember that not all viral infections cause death instantly, and they can remain latent awaiting suitable conditions to infect your stock. Bacterial Infections. Most bacterial infections infect and disrupt the gut lining of the larvae, causing a sort of blood poisoning. The initial signs are often a complete halt in growth, which can last for several days, inactivity and a refusal to feed. This is often followed by shrivelling and darkening of the skin. Some bacterial infections can often end in the same results as a virulent viral infection, and the symptoms can be similar. As a rule of thumb, in bacterial infections the skin does not rupture so easily as with a viral infection, and the black fluid in bacterial infection smells far worse than in a viral infection. Protozoan infection. The well known protozoan infection in Monarchs and other members of the Danaid family, which has the dreadful Latin name Ophryocystus elektroskirrha (called O.e. by most) is species-specific and will not infect any Swallowtail species. At present it is not known if there are any specific protozoans that attack Swallowtails. However, that does not mean that some are not waiting to be detected by science. Fungal infection. Fungal infections produce an amazing array of symptoms, and often these are quite spectacular! The spores spread through filaments throughout the larva internally, and it is only the fruiting aspect for spore distribution that you will see externally on the larval skin. The results are a wide mix of powdery, fluffy or even long erect filaments, with heads like miniature toadstools erupting from the skin. The powdery and fluffy infections are often white, but can also occur in bright colours, of green, pale blue, pink, yellow or even deep red. The filaments are usually white or a dark brown colour. The larvae usually just shrivel in size, and become desiccated and stiff, clinging to their host-plant as these symptoms develop. This can also be seen on pupae that were previously infected as larvae. Page 8

10 Where does disease come from? Most wild Swallowtail stock that you gather, or Swallowtail stock that you receive from another breeder, will have tiny amounts of latent viral, bacterial or fungal infection, at any of their lifecycle stages. Don t be too surprised; the air around us is also full of all these pathogens! However, do be aware that some bred stock received from other breeders may have been subjected to poor conditions, and have larger amounts of pathogens that will erupt as you breed. I always isolate any bred stock that I receive from other breeders until I am satisfied that it is completely healthy. Under normal climatic conditions, butterfly lifecycle stages can easily cope with low level of infection, and these rarely cause problems. That is not to say that in nature there can t be vast die-offs due to a virulent disease, and much work has been done using these pathogens to control crop pests. One of the most common is known as "Bt" (Bacillus thuringiensis), a bacterial concoction that can devastate your stock if sprayed a few kilometers upwind of your farm. Avoiding disease. Most butterfly disease problems are self-induced by the breeder. This is almost always due to providing stressful conditions for the larvae, and providing perfect conditions for the pathogens to reproduce rapidly. Remember that the larvae will already have many pathogens in tiny amounts on their skin. It is exactly the same for humans! When we humans, live in optimum conditions, these bacteria, funguses and latent viruses, cause us no problems, our immune systems deal with this for us. For example think of Meningitis, which many folk have latent inactive amounts of in their nasal cavities. This never normally causes us problems, until conditions are right for it to spread. (Let us not confuse this with virulent Meningitis outbreaks, and other contractible diseases!) So, if we put a healthy human in a damp, hot, dark cell, with poor airflow and crowded with other people, problems will soon develop! Apart from fungal diseases, bacteria and latent viruses can run riot. This is no different from larvae. By keeping equipment clean and sterilized, providing (If possible) growing host-plant, keeping airflow, temperatures and humidity in balance, removing frass regularly and avoiding overcrowding, this will normally overcome all of the problems that you are threatened with. Always remove any dead or sickly larvae immediately, and also remove the leaves they were on. If another larva eats those leaves they will probably also be infected with the disease and die, as well as continuing to pass it on to other larvae. While this will counteract most disease problems that you are likely to encounter, the real threat is from an introduced virulent form of pathogen to your breeding set-up. So I repeat again: isolate new stock until you are sure it is healthy! In the Swallowtail Workshop, Part1: Paper 7, I gave a brief outline on how to avoid disease affecting your set-up. Page 9

11 For clarity, I repeat some of these notes here and expand on them. Disease is a major problem for many butterfly breeders. It can be avoided by ensuring cleanliness and controlling temperatures, humidity and airflow at all stages of the lifecycle. As previously mentioned, you must keep all of your equipment, cages, sleeves, and hands scrupulously clean. Always be aware of cross-infection as you move between equipment and cages. This strict regime of cleanliness will prevent the problems of disease (fungal, bacterial and viral) from occurring in your breeding areas. Keeping a small bottle of hand-sterilizing gel, available from Chemists, is a great way to prevent cross infection. I have one in my pocket at all times, and use it every time I leave one cage and check another. The gel is alcohol-based and evaporates in a few seconds. Another key measure is good airflow. I can t stress enough how important this is to successful breeding. As I have already said, I know that I can t keep all parasitoids out of the main flight-house, so I confine all vulnerable stages in parasitoid-proof netting cages. Doing this enables me to have a much larger, open weave to my flight house shade cloth. If you don t think this would make much difference to you, then place a fan in front of several different weaves and you will be amazed at how much a shade cloth can hold back airflow. One further option that you may like to consider is that, if you have the space and resources, you could have more than one flight-house. I have always liked the idea of leaving land fallow and letting it recover naturally. Wherever I have lived and bred butterflies and had the space, I have always used a rotation system between flight-houses, if possible leaving one to lay fallow. It is important to be aware that disease is often species- or family-specific, so if you are breeding a number of different species, rotation is a great idea. So, let s recap the causes. Disease is induced by: Lack of cleanliness/sterilisation in cages, boxes, and equipment. Also, wash your hands before moving between cages. Cages which are difficult to sterilise. Buy Pop-up cages or construct them out of aluminium or plastic (PVC), and avoid wood components for cages. Too-close contact between cages. If you have the space, keep stock apart from each other. If purging stock becomes necessary, you ll lose less overall! Poor air circulation. Temperatures and humidity are either too low or too high. Dampness in closed plastic boxes with poor airflow. Page 10

12 . Cramped conditions and lack of fresh host-plant Cut wilted host-plants. Always supply fresh, healthy host-plants! Failure to rotate stock between flight cages and different areas. (Sterilise and leave a cage or flight area fallow for a period of time if possible.) Sterilizing options. Grain Alcohol. High-proof grain alcohol is effective and evaporates quickly. I am sure that this offers complete sterilisation. This is a great method to sterilize everything you use except for organic stock such as plants. Grain alcohol can be sprayed using a plant mister, but watch out for two things! Some plastics can dissolve in alcohol, and also the stuff can be very explosive! Watch out for fumes, and never smoke while using it! Bleach. I used to use the bleach that the TV tells me Kills 99% of all known germs (I assume the 1% left are particularly virulent or the companies are just covering themselves against litigation should some pathogens survive!) This I mix up in water at 5% bleach, and zap around the cage until it s soaked and then just leave it there to dry. Sometime later I hose the cage down two or three times before I dry it and use it again. Remember, if you have metal cages, sodium hypochlorite (the active agent in bleach) will eat into the metal if you use too strong a solution. Baby Bottle Sterilizing solution. This is now my favourite sterilising solution. I use this undiluted when sterilising both outdoor enclosures with growing plants, cages and equipment. Being safe for babies and very efficient, I tend to get carried away with this spray. As this solution is far less corrosive than bleach, my plants remain unaffected. I leave this to dry also, and then hose down. This product is available in many countries, but unfortunately not in the US. However I do know of at least one successful commercial butterfly breeder in the US that imports Milton, and has been using it for some years now. Available as a solution or in tablet form. Hand-gel Sterilizing solution. This is a great option to use on your hands when you are working between cages, to avoid cross-infection while handing stock. I keep a small bottle of this in my pocket at all times. The Fallow Period. I like to keep rotating usage of a few outdoor enclosures. This also allows for the fallow period which is a method of sterilisation. Sunlight is a great decontaminant, so remove any shade cloth and let the full sun shine down on the "fallow" cage. Page 11

13 Final Note: I have been keeping my ear open to the general sterilizing options and sterilizing environments used around the world to combat pathogens in many different animal breeding environments. I know that some butterfly breeders have been reporting great results from using a product called Oxine Ah (Animal Health). As a word of caution: I have not been able to experiment myself with this product, but I now offer a link from the Poultry industry that may be of interest. Have a look at this link: and you may like to conduct your own experiments with this product. Dealing with diseased stock. There is no viable option but to destroy all stock that is infected by disease! This may sound harsh, but you really must follow this procedure and incinerate all infected stock. Sterilize all cages and equipment, using the methods described above. You really have to be very thorough here, and I recommend at least two further back-up sterilization procedures. Be very careful with frass, even from un-infected stock. Never add this to your compost heap! Dispose of frass through the trash in a sealed plastic bag. It has been many years since I have had any livestock problems from disease. This is because I am almost fanatical in offering optimum conditions for my stock. Why? Well, I have certainly had my share of livestock disease problems in the past, and I tried all sorts of short-cuts and remedies. All failed! The only way forward is to be thorough and spotlessly clean in your breeding programme, and follow the information in this paper. I wanted to finish this section by showing you an interesting fungal infection. This is an old photo, and I wish it was clearer, but it should illustrate my point. What appear to be perfectly healthy pupae, with no visible signs of disease, have now sprouted a white fungal filament. This infection was contracted in the larval stage, but it was not until the pupae were formed that the filaments from internal fungal infection sprouted and fruited with sporebearing heads. : July Swallowtail Workshop Part 2: Paper 7. Avoiding Parasitoids and disease part 2. Page 12