Pest Management Guidelines
|Progress Towards Pest Management in Litchi|
By: Vincent P. Jones, Carrie H. M. Tome, Christopher J. Robb
Department of Entomology, University of Hawaii at Manoa
Honolulu, HI 96822
This paper will discuss the progress made towards the development of an integrated pest management program (IPM) for insect control on litchi. It will briefly discuss what IPM is, then focus on research progress made in the last year.
Tables and figures referred to in this document are unavailable at this time.
What is pest management and what sort of information is
The textbook definition is "the intelligent selection and use of pest control actions that ensure favorable economic, ecological, and sociological consequences". For our purposes, pest management is preventing economic damage to the crop the best way possible considering as many factors as possible. We are not trying to just suppress one insect's population, but look at all the pests population levels and how they affect the health of the crop. You could conceivably apply pesticides every day and control your pests, but it is economically unfeasible and ecologically it would destroy all your natural enemies. In addition, your neighbor would probably turn you in to the DOA. We are trying to set up a pest management program that works and is sustainable over time.
There are several pieces of information required for an IPM program. First, what are the pests and natural enemies present in the crop? For fruit crops, when does the female attack the fruit? It doesn't pay to protect your fruit when there are no insects present, or when the fruit isn't susceptible to the insect.
Another important piece of information is the differences in damage between cultivars and locations. This information gives you an indication of what sort of damage levels you can expect under certain situations. Along this same line of thought, we also need to have some measure of the population level of the pest and the natural enemies, so we can look and see if the problem is getting worse or better. You don't want to be applying pesticides if the population is getting better on its own, only when it is getting worse. You also need some sort of information on optimal timing of control measures. We are trying to put on the pesticide only when it is required, and before the population comes out, not after half of it is out and the damage is already done. If you put on the pesticide too late, all you're getting is revenge.
Where is the pest when it is not attacking the fruit? In litchi this is critical because oriental fruit fly is a major problem that we have seen this past year, and it does not complete development in litchi except very infrequently. Many eggs are inserted into the fruit, but do not complete development. This means that the population which is damaging the fruit is coming from outside the orchard. Because of this, it is important to know where the pests are when they are not in your orchard.
You need to know the effect of control measures on the natural enemies as well as on the pests. You don't want to put on a pesticide which controls your main pest but which kills off the natural enemies which suppress other pests. This is the sort of information you need before you can make up a pest management program.
Progress on Litchi IPM
I was contacted by the tree fruit growers to investigate this problem on litchi after the harvest was already done (in 1991), and it was felt the damage was primarily from Cryptophlebia, which is litchi fruit moth (Cryptophlebia ombrodelta - known as macadamia nut borer in
Australia) and the koa seed worm (Cryptophlebia illepida). So the
objectives of the study, was first to confirm the identity of Cryptophlebia spp. attacking litchi, and secondly, to estimate what percent crop loss there was from this particular insect. We also wanted to determine the period in time that the fruit was susceptible to feeding by Cryptophlebia, and lastly to survey natural enemies and pests which may be upset in the pesticide applications we use.
The two species of Cryptophlebia found in the islands have similar life histories. The koa seed worm, C. illepida, is endemic to the Hawaiian islands and was first reported in 1919 on macadamia. It has 18 host plants listed of which macadamia, litchi, and mango are the main economically important hosts. Litchi fruit moth is an accidental import from Australia first reported in 1958 with most of the same host plants. The two species look very similar and have basically the same biology. The physical differences between them are that the litchi fruit moth is a bit larger and more robust, and there is a small difference in coloration. Both are found in about equal numbers on litchi, while on macadamia we find about 85 percent koa seed worm and 15 percent litchi fruit moth. The larval stage has off-white skin and dark little platelets on the back with hairs coming out, and a black or dark brown head capsule. Damage seen on litchi is frass or fecal pellets sticking out of the fruit that is generally dry, and if you cut open the fruit, you will find damage and larvae inside the fruit.
Oriental Fruit Fly
Damage to litchi by fruit fly became evident late in the season. The fruit flies seen in the orchard were all Bactrocera dorsalis (Hendel), the oriental fruit fly (OFF). The damage is caused by the female fly during the act of egg deposition (oviposition). The female fly uses the ovipositor at the tip of her abdomen to insert the eggs through the skin of the fruit. The wound is frequently frothy and causes the skin to turn brown around the hole. In a large proportion of the cases, OFF eggs can be seen in the hole or next to it from the outside with a 10x hand lens. When the skin is peeled from the flesh, the inside has a large brown circular mark centered on the oviposition hole. The eggs are often on the surface of the flesh, but can also be found inserted several mm deep into the flesh. Eggs are generally deposited in a batch of more than 10 eggs. Fruit deterioration is hastened by bacteria and/or fungi introduced during the act of egg deposition.
Fruit were held to determine the species of fruit fly and the ability of the fly to complete development in litchi. None of the infested fruit yielded adult fruit flies. In conversations with Dr. Jack Armstrong, USDA Fruit Fly Research Lab Hilo, he indicated that only oriental fruit fly has been seen in their studies and that litchi is a very poor host. Fruit flies can complete development in litchi according to his studies, but the survival rate is extremely low. In our collections we found second and early third instar larvae. This suggests that litchi does not harbor resident populations of OFF; they must disperse into the orchard from alternate hosts.
MATERIALS AND METHODS
Study sites were set up at five different locations: two in Kona near Captain Cook, one on Oahu near Mililani and two on Kauai, one near Kapaa and the other near Princeville. At all sites, we placed pheromone traps, which are synthetic sex lures from the females moths, so that we can collect male moths to determine population changes over time. The pheromone traps work for both koa seedworm and litchi fruit moth. These traps were changed at two week intervals before the end of May 1992, and at approximately one week intervals after this period until harvest. We have collected fruit from different cultivars when possible at each location each time the pheromone traps were changed. The cultivar types and locations are listed in Table 1.
At each location, we tried to collect a minimum of 75 fruit per cultivar per week. This was done by randomly selecting 3-4 trees of a given cultivar and selecting 25 fruit per tree. The samples were shipped to Oahu and fruit size, fruit color, presence of Cryptophlebia eggs or larvae, and fruit fly damage was recorded from each fruit. Because it is not possible to distinguish eggs of the two Cryptophlebia species, egg deposition is recorded only as Cryptophlebia spp. rather than as each species separately. Over all five sites and four cultivars, more than 8,000 fruit were examined for this study. Damage is reported as all samples and the last 2 weeks before harvest. The all sample estimates may be misleading at certain sites because the data were not taken for all cultivars over the entire season. The last two weeks prior to harvest are a good indicator of what the grower finds at harvest time.
Cryptophlebia Species Identity
The litchi fruit moth and the koa seedworm have both been collected at all sites in the pheromone traps. In Kona, the litchi fruit moth population density was approximately 60% lower than the koa seed worm population density throughout the study period. On Kauai, the trends were reversed with litchi fruit moth population levels being higher. On Oahu, the population levels of both moths are extremely low compared to both Kona and Kauai.
The percentage of fruits found with Cryptophlebia eggs varied markedly within a location and between cultivars (Table 2). At the first site on Kauai, there were marked differences between the percentage of fruits with Cryptophlebia eggs present. The cultivar Kwai May-Pink had the highest percentage of fruits with eggs, followed by Kaimana, Kwai Mi and Groff. The Kwai May-Pink sampled at this location were in a different block that the other three cultivars and to some extent the differences in levels may reflect a higher population density in that particular block. However, high egg deposition was also observed on Kwai May-Pink at the first Kona site, suggesting that this is a cultivar specific trait. Egg deposition at the second Kauai site on Kwai Mi and the first Kona site on Kaimana were also high, while that observed on Kaimana at the second Kona site and Kwai Mi and Groff at the Oahu site were quite low.
Table 2. % fruit with eggs from Cryptophlebia spp. present at five different locations.
Table 3. % Fruit Damage to Litchi from Cryptophlebia spp. at five different locations.
Damage from Cryptophlebia did not necessarily follow the egg laying pattern (Table 3). In particular, there was a high proportion of fruits with eggs at the second Kauai site and at the first Kona site, but damage on the Kwai Mi and Kaimana varieties was less then 2.5% and on the Kwai May-Pink approximately 6.67%. This points out that there is a tremendous amount of Cryptophlebia egg mortality occurring on litchi and mere presence of eggs is not a good indicator of damage with will be observed. Instead, the number of eggs laid is a better indicator of potential damage if all conditions are favorable for Cryptophlebia population growth.
Time Fruit are Susceptible
Adult female Cryptophlebia moths have been shown to lay eggs primarily on macadamia nuts that are greater than 20 mm in diameter. We found that also occurs on litchi (Fig. 1). On the cultivar Kwai Mi, ┼ 5% of the eggs were laid on fruit that were less than or equal to 20 mm in diameter. Also, the size-egg deposition relationship remained fairly constant between the different sites (Fig. 1). When looking at the cultivars Kwai May-Pink and Kaimana, it appeared that the moths were laying a greater percentage of eggs on progressively smaller fruit , but even so, at 20 mm, only 8.8 and 3.8% of the fruit had Cryptophlebia eggs present (not enough eggs were laid on the cultivar Groff at either site to determine the relationship for that cultivar accurately). From these data, protection of the fruit before they are 20 mm long appears to have little benefit regardless of the cultivar grown.
Fig. 1. Cryptophlebia oviposition on various fruit sizes on 3 different cultivars at 3 different sites.
Groff litchi appears to be relatively non-susceptible to KSW (Tables 2 & 3). This may be related to the relatively small size of this cultivar (peak average size ┼ 26 mm) and the relatively short period between which it achieves 20 mm in length and harvest begins. At the location on Kauai, the average fruit length was over 20 mm for approximately 21 days, but harvest was occurring during the last two weeks of this period. Studies performed in temperature cabinets have shown that ┼ 8 days is required for egg hatch at 20░C. Therefore, the window in time during which the female moth lays eggs and harvest is quite narrow. For damage to occur on this cultivar in significant amounts before harvest, females would have to be at high population levels just when the litchi are slightly less than 20 mm in diameter. Prompt harvest assures that damage will not be excessive.
The cultivars Kwai May-Pink and Kwai Mi both exhibited a rapid fruit growth and an extended period where they were over 20 mm long. At the Kona site, the Kwai May-Pink was greater than 20 mm in diameter for a period of 55 days, and at the Kauai locations for 49 and 50 days. The Kaimana litchi at Kona was greater than 20 mm for at least 46 days, and on Kauai for at least 44 days. The longer period in time between 20 mm in length and harvest makes a close synchrony between the moth populations and fruit size less important and consequently, the potential damage from Cryptophlebia on these cultivars is greater.
Oriental fruit fly
Regardless of its ability to complete development in litchi, the dispersal of OFF into the orchard and subsequent fruit damage is an extreme problem for litchi growers (Table 4). Damage levels were high on all the cultivars (at least at one of the sites), except for Groff. The most extensive damage was found on the cultivars Kwai Mi (┼ 31% damage) and Kaimana (┼ 28% damage) at the second Kauai site and the first Kona site, respectively.
There is considerable variation in damage within a single cultivar between sites. This probably reflects the fact that because litchi is a poor host to build up OFF populations, most of the damage must come from flies which migrate into the orchard from surrounding vegetation. It is particularly interesting to note that the Kaimana cultivar at the two Kona orchards were less than 1000 yards away from each other, yet the damage levels were ┼ 28% and 0.4%, respectively. The orchard with the lower damage level had coffee interplanted with litchi and was not irrigated, while the other field was a mixed cultivar block in the center of a large tropical fruit orchard. The other interesting comparison is the high damage level on Kwai Mi at the second Kauai site compared the other two locations.
Table 4. Percentage Fruit Damage to Litchi from Oriental Fruit Fly at five different locations.
Time of susceptibility to oriental fruit fly.
As with other crops (such as papaya), the period of fruit fly susceptibility is closely tied to the state of fruit maturity. Because we recorded the color of each fruit as green, 1/3 red, 2/3 red or full red, we were able to determine at which stage most OFF damage occurred. The general trend for all cultivars was that within a site, damage at the green stage was fairly low to non-existent compared to the 2/3 red or full red color (Fig. 2). The Kwai May-Pink cultivar showed an unusual amount of damage on the 1/3 red stage, but this may be related to the difficulty in judging the more yellowish color of this cultivar.
Fig. 2. % Fruit damage by oriental fruit fly on three different cultivars and four different ripeness stages.
Damage at different heights from Cryptophlebia spp. and Oriental fruit fly. At the second Kauai site, we were able to take some samples from high in the canopy and compare the damage to that observed in the
lower part of the canopy. For both species, the damage was significantly higher at the lower elevation (┼ 2 meters) vs. the higher elevation (┼ 7 meters) (Fig. 3). This means that the success of a management program could be determined from samples on the lower branches without fear that the top of the tree is suffering high damage levels.
Fig. 3. Effect of height from ground on damage estimates for oriental fruit fly and koa seedworm.
Does Oriental Fruit fly only attack fruit damaged by Cryptophlebia spp.? One of the questions I was asked was do fruit flies only attack fruits already damaged by litchi fruit moth? The answer to this is clearly no. Damage on a number of the cultivars is much higher from oriental fruit fly than it is from litchi fruit moth. At two of the sites, one in Kona and one in Kauai, there was enough litchi fruit moth and oriental fruit fly damage that we were able to do statistical tests of the association, and the two types of damage were completely independent.
Other Insects and Mites Found on Litchi
There is a wide variety of insects found associated with litchi. Their economic importance varies depending on cultivar, location, orchard cultural practices and treatment history. This makes predicting the pest status or the effect of pesticide applications on non-target species associated with the crop difficult and imprecise at best.
Of the 18 species observed, four are serious pests which must be deal with on a regular basis, 3-4 have questionable pest status, 6 are natural enemies of pest species, and 3 are pollinators (Table 5). To reduce damage from this complex requires a management plan which reduces the pest species, but does not eliminate the natural enemies or the pollinator spp.
There are several pests other than Cryptophlebia and oriental fruit fly which are important. The most widespread pest is the erinose mite which occurs on the leaves. I found this everywhere I worked on litchi. If left to itself, high population levels can develop and leaves are severely deformed.
Spider mites were another problem, particularly in the drier parts of the islands. They caused a significant amount of leaf bronzing, but nobody seemed to care that much; I didn't see any leaf drop, the population seemed to drop off in the warm part of the summer. They are something surely to be concerned about in the future. The predator mites are another thing we have to be concerned with in the sense that they prey on the spider mites and the erinose mites and if we contemplate using pesticides on litchi we have to make sure that the predator mites are not destroyed or you are going to have perennial spider mite and erinose mite problems.
Populations of these two moths can be monitored using pheromone traps which can be obtained from several commercial sources. Trece, Inc. [(408)-758-0205, Salinas California] is the direct supplier. The traps required are the pherocon 1CP and the lures are for the oriental fruit moth (OFM). Locally, Brewer Environmental may be able to special order the traps and lures. Lures should be replaced at 3 week intervals and the bottoms of the traps when they get dirty. The number of moths found in the traps should be recorded at approximately weekly intervals to determine if populations are increasing rapidly at a time when the fruit are susceptible (0.7" in diameter or 18 mm diameter).
Registration of carbaryl is being completed for control of Cryptophlebia. Carbaryl is used in Australia for control of Cryptophlebia and is quite efficacious. Based on our studies, Cryptophlebia do not attack fruit less than about 18 mm in diameter (0.7"). Sprays should not be applied before this time regardless of the population density recorded in pheromone traps. The cultivars Kwai Mi and Groff probably do not have to be treated, but Kwai May Pink will probably require treatment to prevent damage. Kaimana may also need to be protected, depending on the population level in the orchard and the surrounding host plants.
The use of mating disruption has been tried on Cryptophlebia spp. on macadamia in Hawaii. Mating confusion involves using the synthetic sex lure used in pheromone traps to saturate the entire orchard. This is thought to reduce mating because it is difficult for males to find female moths. The trials on macadamia were not a success, although egg deposition was reduced by 50%, significant damage still occurred. Work on this in the future will probably intensify and improved application technology may make this a viable option in the future.
Oriental Fruit Fly
Oriental fruit fly does not complete development to any significant degree in the litchi orchard. They migrate in from the outside and deposit eggs into the fruit, which rarely complete development. However, the act of puncturing of the fruit to lay the egg results in a oozing wound and the introduction of microorganisms into the fruit, rendering it unsaleable. Strategies for management of the insect therefore require that the fly is prevented from moving into the orchard. Because only female flies damage the fruit, all control measures should be aimed at the females.
Traps for monitoring oriental fruit fly should be aimed at the females. Current trapping using methyl eugenol as an attractant are useless for pest management. First, they trap only males and secondly, as stated above, they may have an attractive radius of greater than 1 mile. Considering that most of the tropical fruit orchards are rather small, and that if the traps are placed near the edges, many of the flies trapped are not from your orchard, but instead come from the surrounding region. For pest management, you want a trap with a limited radius of attraction so that you can see what's happening in your orchard. If you want to know population levels outside the orchard, place a trap outside the orchard. Traps which should work for fruit fly attraction are yellow panels coated with tanglefoot (an adhesive) and having an ammonia lure (available commercially from several manufacturers). Alternatively, yellow balls approximately 8.5 cm diameter coated with tanglefoot should provide information on the changes in population levels if trap catch is recorded weekly. Traps should be replaced when dirty or when the lure expires.
Carbaryl, which is being registered for Cryptophlebia spp. on litchi, is not effective against oriental fruit fly, therefore the registration of malathion and a partially hydrolyzed yeast protein bait (Nulure) should be pursued. This combination is generally considered to be the most effective control measure for fruit flies, because the female flies require the protein source for egg production. The malathion generally has a preharvest interval of less than 3 days. For example, the Clean Crop Malathion 8 aquamul has a preharvest interval of 2 days on mango, passion fruit and guava, but on citrus it is 7 days. The downside of this pesticide is that the residue is short-lived, lasting less than 7 days under even the best conditions. However, its low mammalian toxicity means that it would probably be easier to register than other materials. It would be wise to register this material on any tropical specialty fruit that will be sold fresh market. If it is easier to register malathion without Nulure, this should be pursued.
Because of the long period that some of the litchi cultivars are susceptible, a material with a longer residue should be investigated. However, a systemic material is not desirable, because the flies do not complete development in the fruit anyway. A contact insecticide is required. Candidate materials all require the approval of the manufacturer for registration. Before any material is used on a widespread basis, its effects on natural enemies must be tested to prevent what is known as "the pesticide treadmill". The pesticide treadmill is when natural enemies for secondary pests are eliminated by pesticide treatments for a particular pest and then treatment for the other pests is required because their natural enemies are gone. This leads to more and more pesticide use. We currently have few pesticides registered, but all new materials should be introduced with caution.
Other possibilities include any pesticide with a repellent action. This would be particularly effective in litchi because the oriental fruit fly population is primarily moving in from outside the orchard. A neem product (Azatinź) is discussed below and may be good for fruit fly control.
Bait buckets used by some growers only capture adult males. Because males do not damage the crop, this is a "revenge" tactic which costs money, but does nothing to reduce damage. The idea behind the bait buckets is that by trapping out all the males in an area, that females will not be able to mate and lay fertile eggs. However, in litchi, the females are migrating in from outside the orchard and have a flight range of greater than 1 mile. All females may not be mated upon entering the orchard, but it is almost certain that a large proportion are. In studies on other crops where oriental fruit fly can complete development, it is clear that greater than 99% of the males in the area must be trapped out before any reduction in fruit infestation levels are found. This sort of tactic must be applied to a large area. Studies by the USDA fruit fly laboratory have shown that a 63 hectare papaya field with a very high density of bait buckets (or other dispensers) were not able to reduce damage levels.
Malathion can now be used on the windbreak trees to reduce immigration into the orchard (see the Hawaii Tree Fruit Journal #2 for information). In high population levels, this may not be very effective, but in areas with low population levels, spraying the windbreak trees with malathion and Nulure (protein bait) will provide some relief for growers.
When a pesticide is registered for fruit fly control, they should not be applied until the fruit begin to color. While green, we almost never saw any damage. The Kwai may pink cultivar, which is somewhat yellowish, should be watched closely because it and hard to determine exactly when it begins to change
Litchi Erinose Mite
This mite is easily controlled by sulfur, but sulfur is not registered on litchi. Studies in Australia have shown that erinose mite moves between trees by traveling on honeybees (and probably large flies, etc.). Erinose mite can probably be controlled using Safer's Insecticidal Soap, if the coverage is good. Coverage is extremely important, because Safer's has no appreciable residue and kills entirely by contact. A benefit of using Safer's is that it is generally not toxic to predaceous mites which help keep erinose mite populations regulated.
Future Candidate Pesticides. The industry should pursue the registration of materials which may control pests not currently found within the state. A good candidate is Azatinź which is an extract of the neem tree, Azadaractica indica. This product now has a very favorable registration category which allows registration with very minimal testing - the industry must request it and phytotoxicity tests must be run according to the manufacturer. Azatinź has activity against whiteflies, thrips, and lepidopterous larvae. It also acts as a repellent in some trials and may therefore be a good candidate for helping reduce oriental fruit fly damage. As with any pesticide, the effects on natural enemies must be examined.
Use pesticides safely. Follow the pesticide label. Consult with the Cooperative Extension Service or the Hawai'i State Department of Agriculture for authorized special local need registrations or additional information. The user is responsible for the proper use, application, storage, and disposal of pesticides.
Reference to a company or product name does not imply approval or recommendation of the product by the College of Tropical Agriculture and Human Resources, Cooperative Extension Service, University of Hawai'i, or the United States Department of Agriculture and does not imply its approval to the exclusion of other products that may be suitable. All matenals should be used in accordance with label instructions or manufacturers' directions.